Pulmonary Uptodate

COVID-19 origins: Closest viruses to SARS-CoV-2 found in Laos

Since SARS-CoV-2, the virus that causes COVID-19, was first detected in Wuhan, China, in December 2019, there have been global efforts to determine its origins.

As the pandemic was thought to originate in Wuhan, many efforts have focused on China, with the assumption that, as the virus was first detected there, it probably started there.

Now, two papers under review by the journal Nature and published as preprints are casting some doubt on these assumptions and indicate that in order to discover the origins of the virus, researchers may have to look farther afield.

Infecting human cells
One of the reasons SARS-CoV-2 is so infectious is a region on its spike protein that gives it its ability to bind to a receptor present on the surface of many human cells called ACE2.

In a paper submitted to Nature, researchers from the Pasteur Institute in Paris, France, and from Laos have now reported finding viruses with receptor binding domains very similar to those found on SARS-CoV-2 in cave bats in North Laos.

The researchers took blood, saliva, a**l f***s, and urine samples from 645 bats from 46 different species found in limestone caves in North Laos, which is close to the Southwest China border.

They discovered three separate virus strains in three different species of Rhinolophus bat, commonly known as horseshoe bat. RNA sequencing revealed that these viruses were over 95% identical to SARS-CoV-2, and one, the closest virus to SARS-CoV-2 found so far, was 96.8% similar.

Further experiments showed that the receptor binding domain of the viruses had a high affinity for human ACE2 receptors. This was comparable to the affinity of SARS-CoV-2 strains that scientists discovered at the beginning of the pandemic, suggesting these viruses could infect humans directly.
Not the ‘China virus’ after all?
Further doubt was cast on the assumption that the virus responsible for the COVID-19 pandemic originated in Wuhan with another preprint submitted to Nature.

A study by a team from the Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing has suggested that SARS-CoV-2-related viruses are “extremely rare” in bats in China, after taking nose and a**l swabs from over 13,000 bats between 2016 and 2021 at 703 locations across the country.

The paper also showed that SARS-CoV-2 was undetectable in samples taken from Wuhan Huanan Market, 40 days after the closure of the market, which was due to fears that the initial infection event had occurred there.

Authors conclude that further research should be done south and southwest of China to determine whether the SARS-CoV-2 virus originated there.

Finding the origins of SARS-CoV-2
One of the reasons it has been so hard to establish where the coronavirus originated is viral genomes that change through a process called recombination, rather than just through mutations. Viral recombination occurs when two different strains infect the same host cell.

As they replicate in the same cell, they can interact, and the virus progeny they generate can have some genes from both parents. This can make it hard to work out the lineage of that virus.

“Recombination seems to be important for how these viruses evolve overall,” Spyros Lytras, an evolutionary virologist from the University of Glasgow in the United Kingdom, told MNT.

“So, essentially we are saying these viruses switch bits of their genome all the time, and the new viruses from Laos really highlight that. Even though [these viruses] are found in the same place, the same cave essentially, they all have different bits of their genome that have different combinations of recombinant parts.”

Last year, scientists detected a similar virus in Yunnan, in Southwest China. It was 96.1% similar to SARS-CoV-2, meaning the present paper describes the closest virus detected yet.

Not the ‘China virus’ after all?
Further doubt was cast on the assumption that the virus responsible for the COVID-19 pandemic originated in Wuhan with another preprint submitted to Nature.

A study by a team from the Chinese Academy of Medical Sciences and Peking Union Medical College in Beijing has suggested that SARS-CoV-2-related viruses are “extremely rare” in bats in China, after taking nose and a**l swabs from over 13,000 bats between 2016 and 2021 at 703 locations across the country.

The paper also showed that SARS-CoV-2 was undetectable in samples taken from Wuhan Huanan Market, 40 days after the closure of the market, which was due to fears that the initial infection event had occurred there.

Authors conclude that further research should be done south and southwest of China to determine whether the SARS-CoV-2 virus originated there.

Finding the origins of SARS-CoV-2
One of the reasons it has been so hard to establish where the coronavirus originated is viral genomes that change through a process called recombination, rather than just through mutations. Viral recombination occurs when two different strains infect the same host cell.

As they replicate in the same cell, they can interact, and the virus progeny they generate can have some genes from both parents. This can make it hard to work out the lineage of that virus.

“Recombination seems to be important for how these viruses evolve overall,” Spyros Lytras, an evolutionary virologist from the University of Glasgow in the United Kingdom, told MNT.

“So, essentially we are saying these viruses switch bits of their genome all the time, and the new viruses from Laos really highlight that. Even though [these viruses] are found in the same place, the same cave essentially, they all have different bits of their genome that have different combinations of recombinant parts.”

What to know about the different COVID-19 vaccines

Pfizer-BioNTech
It uses a lipid, or a fatty acid, to deliver a piece of the virus’s genetic code. However, it does not contain the virus — rather, it contains a piece of messenger RNA (mRNA) that codes for the virus’s unique spike protein.

The body responds to this spike protein as an intruder and develops the immune reaction it needs to fight it. The vaccine teaches the body how to fight the COVID-19 virus when it encounters the real thing.

The vaccine’s contents leave the body and do not alter a person’s genetic code.

It does not contain:

gelatin
fetal cells
latex
eggs or other common allergens
latex
preservatives
metals
antibiotics
Approval status
The FDA has approvedTrusted Source the vaccine for individuals over the age of 16. It has an emergency use authorization for people over the age of 5 and for booster shots.

Dosage
The initial series is two injections, at least 21 days apart, and a booster requires a third shot.

The dosage is:

Ages 5-11: two 0.2 milliliter (mL) doses
Ages 12-15: two 0.3 mL doses
Ages 16 and older: two 0.3 mL doses
It is safe to mix and match this vaccine with others.

Side effects
The vaccine’s side effects are typically mild, and some people report having more side effects after the second vaccine.

They commonly report cold and flu-like symptoms such as:

fever
headache
muscle aches
soreness at the injection site
nausea
chills
fatigue
The side effects usually disappear within a few days. They happen because of the immune system’s reaction to the injection, so having side effects shows that the vaccine is working.

Efficacy
According to the CDC, the full series of the vaccine is more than 95%Trusted Source effective at preventing laboratory-confirmed COVID-19 infections in adults who are not immunocompromised and have no documented history of a COVID-19 infection.

In children ages 5–15 and people with immunocompromising conditions, the vaccine was at least 90% effective.

Among adults without immunocompromising conditions between March 11 and August 15, 2021, the vaccine offered 88% efficacy against hospitalization. This time period extends into the Delta wave of the pandemic.

Preliminary data from Pfizer showed that three doses of the vaccine could neutralize the Omicron variant.

Other research is still ongoing. A 2022 studyTrusted Source found that in a lab setting, a booster could offer some immunity to Omicron.

Moderna
The Moderna vaccineTrusted Source, also called Spikevax, is an mRNA vaccine

Overview
Although it works similarly to the Pfizer vaccine, it delivers a slightly higher dose.

Like Pfizer, it contains mRNA that gives instructions for fighting the spike protein on the COVID-19 virus. This produces an immune reaction that trains the body to fight the virus if it encounters it in the real world.

The vaccine’s contents leave the body and do not alter a person’s genetic code. It does not contain any of the following:

viruses
bacteria
fetal cells
eggs
preservatives
metals
antibiotics
latex
Approval status
The FDA has approvedTrusted Source the Moderna vaccine for adults ages 18 and over. It also has an emergency use authorization as a one-dose booster 5 months after receiving another vaccine.

Moderna is not approved for use in children.

Dosage
The initial Moderna series requires two injections, with a third shot as a booster.

It has earned an emergency use authorization for people over the age of 18. Each dose is 0.5 mL, and the two shots should be at least 28 days apart.

Like the Pfizer vaccine, it is safe to mix and match this vaccine with others.

Side effects
Because they are both mRNA vaccines, the side effects of Moderna are similar to those of Pfizer.

Some people report mild cold or flu-like symptoms shortly after getting vaccinated with side effects more frequently appearing after the second vaccine than the first. Some common side effects include:

headache
fatigue
chills
fever
body aches
gastrointestinal issues
redness, swelling, and pain at the injection site
Efficacy
Among adults without immunocompromising conditions between March 11 and August 15, 2021, Moderna was 93% effective Trusted Source against hospitalization due to COVID-19. This time frame includes the Delta wave, but not Omicron.

A 2022 study Trusted Source found that an additional Moderna booster dose could provide some immunity against the Omicron variant while the two-dose series did not. Moderna is working on a booster specific to new variants.

Johnson & Johnson
The J&J/Janssen vaccineTrusted Source is a single-shot viral vector vaccine.

Overview
Unlike Pfizer and Moderna, it is not an mRNA vaccine. Instead, it works similarly to traditional vaccines.

The vaccine uses a weakened form of a harmless adenovirus that delivers genetic code for the unique COVID-19 spike protein. This creates an immune reaction that prepares the body to fight COVID-19. The vaccine’s contents leave the body and do not alter a person’s genetic code.

It cannot infect a person with COVID-19 or the adenovirus, and it does not contain:

preservatives
antibiotics
metal
latex
fetal parts
eggs
The injection is generally less effective than the Moderna and Pfizer vaccines.

The CDC urges people to choose the mRNA vaccines unless they are inaccessible. While J&J/Janssen is safer than going unvaccinated, it may have worse side effects than other vaccines.

Approval status
The FDA has approvedTrusted Source the vaccine on an emergency use authorization basis for people over the age of 18. It has also given emergency use authorization for a booster at least 2 months after the first dose.

The vaccine is not approved for children or anyone under the age of 18.

Side effects
The most common side effects of this vaccine include mild cold or flu-like symptoms such as nausea, fever, chills, and muscle aches.

Very rarely, however, a person may develop a blood clot.

The CDC estimates that roughly 3.83 people per millionTrusted Source will have this side effect. However, the blood clot rate is much higher with a COVID-19 infection, with as many as 1 in 5 peopleTrusted Source experiencing a blood clot. Of 18.2 million J&J/Janssen vaccine recipients, just 57, or 1 in more than 300,000Trusted Source, have reported blood clots.

Dosage
The J&J/Janssen vaccine is a single-dose vaccine. It has an emergency use authorization in the United States for people over the age of 18.

A person can also get a single dose booster, but the CDC recommends choosing Pfizer or Moderna instead. It is safe to mix and match this vaccine with others.

Efficacy
Between March 11 and August 15, 2021, a time period that included the Delta wave but not Omicron, the J&J/Janssen vaccine was 71% effective in preventing COVID-19 hospitalization.

Oxford AstraZeneca
The Oxford AstraZeneca vaccine works very similarly to the J&J/Janssen vaccine.

Overview
It uses an adenovirus to deliver the COVID-19 spike protein into the body. This creates an immune reaction that trains the body to fight the virus if it encounters it again.

Approval status
The AstraZeneca vaccine does not have FDA approval in the United States. However, it is popular in Europe because it is less expensive to produce than mRNA vaccines and is easier to store.

Dosage
The World Health Organization (WHO)Trusted Source recommends two doses of 0.5 mL each, and the vaccines should be 8 to 12 weeks apart. It is safe to mix and match this vaccine with others.

Side effects
Some common side effects includeTrusted Source:

fever
chills
muscle aches
flu and cold-like symptoms
pain at the injection site
In rare cases, the AstraZeneca vaccine may cause blood clots. The risk of blood clots from COVID-19 is exponentially higher.

Efficacy
The AstraZeneca vaccine prevents symptomatic infection in 6 out of 10 people. Early trials, prior to Delta and Omicron, showed an 80% efficacy at preventing hospitalization.

Novavax
The Novavax vaccine uses older vaccine technology — specifically, a protein subunit.

Overview
This vaccine delivers an antigen synthesized from the COVID-19 spike protein to train the body to fight the virus. It does not contain a live virus, and the spike antigen cannot replicate.

Approval status
Novavax is not yet approved for use in the U.S., but a request for an emergency use authorization has been submitted. As of November 2021, it is approved for use in Indonesia and the Philippines.

Dosage
The WHO recommendsTrusted Source two 0.5 mL doses given 3–4 weeks apart.

It is safe to mix and match this vaccine with others.

Side effects
Side effects include:

fatigue
headache
fever
muscle pain
injection site swelling, pain, and redness
Efficacy
In clinical trials, the efficacy of Novavax against mild, moderate, and severe disease was 90%Trusted Source. Researchers do not know if it prevents infection or transmission and are conducting additional research.

Here's Why COVID-19 Impacts Your Ability to Smell
A new study finds that damage to nasal tissue may be the reason some people lose their sense of smell after having COVID-19.
Experts say this is actually a good sign because tissue may recover more quickly than nerves.
Smell training is one way people may be able to recover their sense of smell.
One distinctive symptom of COVID-19 remains the loss of sense of smell and taste that can affect people for weeks or months after developing the disease.

The decreased or altered sense of smell, called olfactory dysfunction, was originally thought to be due to damage of the olfactory nerves. But new research published this week in The Laryngoscope Trusted Source finds that loss of smell due to COVID-19 may also be because of swelling and blockage of the nasal passages.

Originally the loss of taste and smell due to COVID-19 was thought to be damage to the olfactory nerve. While evidence was limited for a direct relation between SARS-CoV-2 and abnormal brain findings, the theory was that the olfactory dysfunction was due to the olfactory nerve Trusted Source.

They found a prevalence of an olfactory cleft abnormality. The olfactory. Researchers combed through medical reports that detailed changes in olfactory structures through imaging tests of patients with COVID-19. cleft is the channel through which airborne molecules reach the olfactory neurons, which connect to the brain in order to determine smells. In patients with COVID-19 and olfactory dysfunction, the cleft abnormality was 16 times higher.

This means that a contributing factor of the loss of smell and taste is due to the tissues instead of nerves.
The good news is that cells turn over and heal much more easily than nerve damage.

Can loss of sense of smell and taste be returned?
the symptoms are reversible as time goes on and cells turn over. It’s not permanent.”
and recovery times vary widely from one to three weeks to months or years.

“While there are limited treatment options, people have been using smell training as a treatment option with mixed outcomes.
Smell training involves smelling items like specific scents of items like oranges or coffee grounds.
vaccination may alleviate symptoms but clarified that there is no definitive proof of that yet.

However, it is important to note that the findings may not fully account for people living with the extended loss of sense of smell or taste. More research will have to be conducted.

Long COVID's cardiovascular implications
It is unclear how many people around the world live with long COVID. However, one study that is yet to undergo peer review estimates that as of August 2021, about 43% of people who tested positive for COVID-19, and more than half of those who received hospitalized care for this disease, ended up developing long COVID.

The results of a survey published in eClinicalMedicineTrusted Source in August 2021 indicate that long COVID causes an array of diverse symptoms that “affect multiple organ systems, with impact on functioning and ability to work.”

The authors of this paper also point out that people with long COVID experience some unexpected conditions in the aftermath of their initial illness, including a hard-to-diagnose syndrome known as POTS.
POTS involves a complex mix of symptoms, including lightheadedness, brain fog, fatigue, headaches, blurry vision, heart palpitations, and nausea. These symptoms are linked to either low blood pressure or high blood pressure — hypotension or hypertension, respectively — although the precise cause behind these effects remains a subject of debate.

Other dataTrusted Source indicate that acute COVID-19 can lead to various cardiovascular complications, including stroke, heart attack, arrhythmia, deep vein thrombosis, and pericarditis, which is inflammation of the heart membrane.

A study that appeared in Nature MedicineTrusted Source in February 2022 goes so far as to suggest that people who develop COVID-19 have an increased risk of experiencing cardiovascular problems a year after the initial disease.

According to the study authors, at 12 months post-COVID-19, people continue to have an increased risk of “cardiovascular diseases, including cerebrovascular disorders, dysrhythmias, inflammatory heart disease, ischemic heart disease, heart failure, thromboembolic disease, and other cardiac disorders.”

What is more, they write, “The risks were evident regardless of age, race, s*x, and other cardiovascular risk factors, including obesity, hypertension, diabetes, chronic kidney disease, and hyperlipidemia; they were also evident in people without any cardiovascular disease before exposure to COVID-19.”
Cardiovascular complications of COVID-19
According to Dr. Fedorowski, “around somewhere between 1% and 10% of individuals [who contracted SARS-CoV-2] will develop all these [cardiovascular] complications, [such as] myocarditis, pericarditis, and even blood clots building in [the] arteries.”

The difficulty in treating these cases, moreover, is due to the fact that the cardiovascular impact can be difficult to pinpoint at first.

“We are talking about very small blood clots in very small arteries — they are not so easy to detect,” said Dr. Fedorowski. “But some patients may report having blue fingers out of nowhere, just being infected a few days before. And this might be a sign of a very small, tiny blood clot in [the] peripheral blood arteries.”

The Nature Medicine study that we referred to earlier in the article shows that there is an increased risk of a whole range of cardiovascular outcomes even in those not admitted to hospital with severe COVID-19 — that is, even in milder cases of the disease.

To reach this conclusion, the study authors a**lyzed data from a large cohort of “153,760 individuals with COVID-19, as well as two sets of control cohorts with 5,637,647 (contemporary controls) and 5,859,411 (historical controls) individuals.”

This ongoing risk of cardiovascular issues does not apply only to adults. According to a paper in CirculationTrusted Source in November 2020, children can also experience acute heart failure weeks after having had a SARS-CoV-2 infection. This is likely to be an effect of long COVID in children, a phenomenon that is also under investigation.

However, the syndrome that has been puzzling scientists the most in terms of its association with long COVID has been POTS
What is POTS, really?
The medical community generally describes POTS, the syndrome that is affecting more and more people with long COVID, as a dysautonomic phenomenon — that is, something that affects the autonomic nervous system.

The autonomic nervous system is the body’s “autopilot mode,” which controls key bodily functions, such as heart rate, breathing, and digestion.

POTS is one of several forms of dysautonomia, alongside neurocardiogenic syncope, which involves frequent fainting spells, and multiple system atrophy, a rare and fatal condition that leads to rapid systemic deterioration.

The symptoms of POTS are as numerous as they are varied, ranging from lightheadedness upon standing up from a seated position, to tachycardia (an abnormally rapid heart rate), shortness of breath, and digestive symptoms.

This heterogeneity of symptoms can make POTS difficult to diagnose. Doctors often mistake it for an anxiety disorderTrusted Source, as symptoms such as a rapid heart rate and heart palpitations also occur in people who experience anxiety.

“The problem with POTS is that it seems to be not only a cardiovascular problem — [a] heart and vessel problem — [but also] a problem of your nervous system, sometimes on your gastrointestinal system,” Dr. Fedorowski explained.

“And in the end, we call it ‘dysautonomia,’ as it seems [to be] about your autonomic nervous system, which controls all your autonomic functions […]. And as the autonomic nervous system controls, first of all, your circulatory system, the main symptoms that you feel are from the circulatory or from your heart palpitations or blood pressure instability — you don’t feel good when you stand up and so on. But the problems are a little bit diffused,” he noted, pointing out that even top specialists may find it hard to diagnose POTS correctly.What causes POTS?
The causes of and mechanisms behind POTS remain unclear, but ongoing research is searching for the likeliest explanations.

A study published in February 2022 in Cells found that people with POTS have platelet storage pool deficiency, a phenomenon linked to symptoms such as frequent nosebleeds, dysmenorrhea, easy bruising, and anemia.

It also showed that people with POTS have elevated inflammatory biomarkers, all of which may suggest a state of chronic inflammation.

“[T]he data provided [in this study] suggest that POTS is a mixed inflammatory pattern disease,” the authors conclude.

POTS before and after COVID-19
Although more and more media content has started looking at POTS as a long-term effect of SARS-CoV-2 infections, POTS itself is not a newly emerged syndrome.

According to data that the nonprofit organization Dysautonomia International cited well before the pandemic, an estimated 1–3 million people in the U.S. lived with POTS.

Although it is unclear how many more people are seeking care in the aftermath of COVID-19 than they were pre-pandemic, anecdotal reportsTrusted Source seem to indicate a steep increase in cases, most of them associated with long COVID.

Ms. Meriquez Vázquez described her experience of POTS as a life altering syndrome, and she confirmed the similarity between symptoms of POTS and those of a panic attack:
Who is at risk of POTS, and why?
Current data indicate that the people who most commonly receive a diagnosis of POTS in long COVID are young females.

Both Dr. Fedorowski and Dr. Chung, however, noted that there is a slight difference in the demographics of people presenting with POTS before the COVID-19 pandemic and those who have POTS that is associated with long COVID.

As a result, whereas pre-pandemic, most people with POTS tended to be in their teens or early 20s, people with long-COVID-associated POTS tend to be in their 30s, 40s, and 50s, according to the researchers.

As to why that may be, Dr. Fedorowski speculated that the high levels of stress that women in these demographics often encounter — as many juggle workplace responsibilities with child care and take on the vast load of chores in the home — may well predispose them to developing dysautonomia following COVID-19.

“A lot of younger women […] get affected by POTS as a consequence of COVID-19,” Dr. Fedorowski told Medical News Today. “And if you talk to them […], then you will see a picture of a woman who is working very hard, having [a] family, taking care of children, and trying to reach some higher position in […] society; or [there] are the women who are very much stressed by feeling that they are not good enough.”How to treat POTS
Although POTS is an incurable condition, some medical interventions can improve its management. A mix of appropriate medication, physical therapy, and some lifestyle or behavioral interventions can help, according to the Johns Hopkins POTS Program.

Ms. Meriquez Vázquez noted that she has had to modify some of her habits to make her symptoms more manageable.

“I have to keep my blood pressure up with salt and a lot of water,” she said. “So, I take salt pills throughout the day to keep my blood pressure even. But one of the long-standing symptoms that I’m still dealing with is increased migraines. So the longer I spend upright during the day, the more likely [it is] I’ll end the day with a pretty severe migraine,” she explained.

This high and constant level of stress may well, he hypothesized, be a key factor in this demographic’s risk of POTS, which may also make it difficult to prevent.Although physical therapy can be tricky because, like Ms. Meriquez Vázquez, many people with POTS find that exercise worsens their symptoms, researchers continue to investigate the best ways of striking a balance between rest and physical activity.

At the Karolinska University Hospital, said Dr. Fedorowski, “we treat our patients with drugs that regulate heart rate, we treat our patients with drugs that act on the vessels and increase blood pressure in those who have low blood pressure and have difficulty standing up.”

One case study that BMJ Case Reports published in June 2021 outlined the potential of ivabradine, a drug that doctors typically use to treat heart failure, in the treatment of POTS.

“We are [also] using drugs that are working on different receptors, like muscarinic receptors, to counteract muscle weakness,” said Dr. Fedorowski. “We are trying out drugs against brain fog [that] otherwise have been used to fight or to treat ADHD [attention deficit hyperactivity disorder].”

The research on long-COVID-associated POTS and the best treatment methods for this syndrome continues, and there is hope that, in the not-too-distant future, targeted medication may solve what has, so far, seemed unsolvable.

COVID-19: Does Omicron cause less damage to the lungs?

Animal studies and experiments involving cells cultured in the laboratory suggest that the Omicron variant may have a reduced ability to infect the lungs, compared with the Delta variant.This could explain why the Omicron variant appears to cause less severe disease than the Delta variant.
These studies indicate that the Omicron variant could be more efficient at infecting the upper airways than the Delta variant, potentially explaining its increased contagiousness.
The ability of the Omicron variant to escape neutralizing antibodies may also be responsible for its increased transmissibility.
All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub and follow our live updates page for the most recent information on the COVID-19 pandemic.

Early reports following the emergence of the Omicron variant suggest that the variant is more likely to cause less severe illness than previous variants of SARS-CoV-2.

Sequencing of the Omicron genome suggested that this variant carries a large number of mutations, including on the spike protein. The large number of mutations carried by Omicron could be a potential reason for this reduction in illness severity.

However, the milder disease due to an Omicron infection could also be a result of a person’s enhanced immunity, acquired due to vaccination or past SARS-CoV-2 infections.

Although an increase in immunity may influence the severity of illness, studies in animals and cells cultured in the laboratory suggest that the mutations carried by the Omicron variant have made it less efficient at infecting the lungs than the Delta variant. This could explain the less severe illness that the Omicron variant causes.
Laboratory and animal studies
The SARS-CoV-2 virus can affect both the upper and lower respiratory tracts. The upper respiratory tract consists of the nose, sinuses, and throat, whereas the lower respiratory tract includes the trachea and the lungs.

Mild illness or early SARS-CoV-2 infections are likely to involve upper respiratory tract symptoms, such as a runny nose and sore throat.

Severe illness due to the wild-type SARS-CoV-2 and the previous variants oftenTrusted Source involves the infection and inflammation of the lungs.

Inflammation can cause fluid to accumulate in the air sacs, or alveoli, in the lungs, reducing the capacity of the lungs to transfer oxygen to the blood.

Scientists have conducted experiments using animal models and laboratory cultures of lung cells to characterize the ability of Omicron to infect the respiratory tract and cause severe illness.

This includes a study carried out at the University of Hong Kong that used human lung cells cultured in the laboratory, to a**lyze the ability of the Omicron variant to infect the lungs. These cells were cultured from lung tissue removed during treatment of the lung. Typically, this tissue is discarded.

In the study, Omicron replicated 70 times faster than Delta in the human bronchi, which are the tubes connecting the trachea with the lungs. However, it was less efficient at replicating in the lung tissue than Delta and the wild-type SARS-CoV-2.

Other research groups have compared the ability of the Omicron, Delta, and other SARS-CoV-2 variants to cause illness in animal models, such as hamsters and mice.

There is a link between infection with the Delta and other variants and weight loss in hamsters and mice after 1 week, with some data suggesting a correlation between increased virus levels in the respiratory tract and weight loss.

However, various research groups have independently shown an absenceTrusted Source of such weight loss in hamsters and mice after an Omicron infection.

Moreover, these studies found that the hamsters with an Omicron infection showed higher or similar levels of virus, compared with the wild-type SARS-CoV-2 and the Delta variant in the upper respiratory tract. By contrast, the researchers observed lower levels of the virus in the lower respiratory tract after infection with the Omicron variant, compared with the Delta variant.

In sum, these studies show that Omicron may be less efficient at infecting the lungs. Significantly, these animal studies show that an Omicron infection results in lower levels of inflammation and injury to the lungs.

Consistent with this, there is growing evidence suggesting that people with an Omicron infection are less likely to be hospitalized or to require intensive care unit admission or mechanical ventilation than individuals with the Delta variant.

“A number of laboratory-based studies have now shown that the Omicron variant is less able to infect the lungs as well as other variants and, as a result, is leading to less patients being admitted with pneumonia who require oxygen and ventilators.”

“However, hospitalizations and deaths lag behind overall case counts, and as our cases are continuing to rise and set daily records, we ultimately need to wait several more weeks to get a full picture of disease severity .

A shift in preference for cell entry pathway
A potential reason for the less severe infection of the lower respiratory tract by Omicron in the present studies could be the changes in the ability of this variant to enter cells in the lower respiratory tract.

The Omicron variant carries a large number of mutationsTrusted Source in the gene encoding the spike protein, which is expressed on the surface of the SARS-CoV-2 virus.

The SARS-CoV-2 spike protein binds to the ACE2 receptor expressed on lung cells and helps the virus enter the cell. The cleavage of the spike protein by an enzyme called TMPRSS2Trusted Source present on the surface of human cells is necessary before the fusion of the virus membrane with the human cell membrane can occur.

The SARS-CoV-2 virus can also enter human cells by an alternative pathway. This pathway involves the engulfment of the virus by endosomes, which are membrane-bound sacs present inside the cell.

Studies using laboratory-cultured cells suggest that mutations in the spike protein of Omicron have altered its ability to enter human cells with the help of TMPRSS2.

These studies have found that the Omicron variant is less effective at infecting laboratory-cultured lung cells expressing TMPRSS2 than the Delta variant.

By contrast, Omicron is more effective than Delta at infecting cells that allow cell entry through the endosome pathway.

The ACE2 receptor and TMPRSS2 are expressed at higher levels in cells obtained from the lower respiratory tract of humans than in cells from the upper respiratory tract. This could potentially explain why the Omicron variant may be less effective at infecting the lower respiratory tract and causing severe disease.

The interaction of the SARS-CoV-2 spike protein and TMPRSS2 is also involved in mediating the fusion of infected human cells with adjacent uninfected cells.

The reduced ability of the Omicron spike protein to utilize the TMPRSS2 enzyme also limits its ability to infect adjacent cells. This could further contribute to the lower severity of lower respiratory tract infection due to COVID-19.

These results are from cell culture and animal studies. Therefore, human studies are necessary to establish that such a change in Omicron is responsible for its reduced ability to infect lung cells.

“The Omicron variant is interesting in that it appears to swap preferences for entry pathway compared to Delta and prior variants. As a result, it is less efficient at infecting lung cells but more efficient at infecting many upper respiratory tract cells.”

“This correlates with the pattern of disease observed in Omicron — while lower lung pathology is observed, upper airway disease is often more common,” he concluded.

Increased transmissibility
In addition to causing less severe illness, the Omicron variant is also more transmissible. The animal and cell culture studies also suggest that Omicron may be more efficient at infecting the upper respiratory tract.

Studies conducted during the early stage of the pandemic show an association between levels of SARS-CoV-2 in the upper respiratory tract and increased transmission.

The faster replication of Omicron in the upper respiratory tract may thus explain its increased contagiousness.

“[These studies] give rise to an attractive speculation that the increased replication in upper airway tissues may contribute to increased transmissibility, potentially both by increasing the exhaled viral load and by decreasing the number of viral particles needed to infect, although, to my knowledge, this has not been demonstrated definitively,” Dr. Kasson explained.

The increased contagiousness of the Omicron variant may also be due to its ability to escape detection by antibodies.

Previous SARS-CoV-2 infections and immunization with COVID-19 vaccines lead to the production of antibodies that neutralize the virus. These neutralizing antibodies tend to predictTrusted Source the level of protection against a SARS-CoV-2 infection.

The vaccines against COVID-19 have been designed to induce an immune reaction against the spike protein of the wild-type SARS-CoV-2 strain.

The presence of the mutations in the spike protein of the Omicron variant suggests that this variant may escape neutralization by antibodies.

A study led by researchers at the MRC-University of Glasgow Centre for Virus Research in the United Kingdom has shown that the Omicron variant can escape neutralization by antibodies in individuals immunized with the AstraZeneca COVID-19 vaccine. This could be another reason for the high transmissibility of the Omicron variant.

Although scientists need to carry out more research before we can draw solid conclusions, the characteristics of this new variant are slowly being revealed.