International health officials are closely monitoring the spread of a new Omicron subvariant known as XBB, which is poised to trigger a wave of new COVID-19 infections this winter.
Early, limited data suggests the XBB variant may be much better at evading vaccines and other earned immunity, and it also may have an impact on how well monoclonal antibody treatments work in preventing COVID-19 spread.
Some experts believe that symptoms common in XBB variant illnesses will be slightly different from those recorded in earlier outbreaks, partially because vaccines have adapted how immune systems respond to COVID-19 illness over time.
Below, you'll learn: What exactly is the XBB variant; potential XBB variant symptoms to be aware of; and how effective vaccines are at preventing XBB spread.
As more information about the coronavirus pandemic develops, some of the information in this story may have changed since it was last updated. For the most up-to-date information on COVID-19, please visit online resources provided by the CDC, WHO, and your local public health department.
More evidence is mounting that a new group of Omicron subvariants — primarily the XBB variant, a dynamic mutation that is a blend of earlier Omicron offshoots, as well as BQ.1 and BQ.1.1 — may likely trigger a wave of serious breakthrough COVID-19 cases across the nation this winter.
Officials at the Centers for Disease Control and Prevention (CDC) say that the XBB variant isn't fueling a rapid spread of COVID-19 currently, but data sourced from international agencies in Asia suggests that it's proving to be the most immune-evasive form of SARS-CoV-2 scientists have seen since the pandemic began. Health officials are now attempting to closely track the spread of this particular variant among domestic communities after the World Health Organization (WHO) declared that XBB has been recorded in 26 different countries so far; researchers in Singapore have well documented how the XBB variant quickly overtook BA.5 as the most dominant strain in just a few weeks.
That's why XBB has earned the moniker of the "nightmare" variant, as officials and local experts alike are thinking ahead of the potential reality of another COVID-19 wave here in the United States — similar to the initial Omicron outbreak recorded over the 2021 holiday season.
With holiday family gatherings quickly approaching, it is vital to give your #COVID19 vaccine an update. Everyone who is at least 5 years old and has completed a primary COVID vaccine series can get an updated COVID vaccine. https://t.co/F2nLA7DZLV #VaxUpAmerica pic.twitter.com/ePB7JEDI0h
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But healthcare experts in the United States say there isn't enough data currently to discern just how viral the strain is compared to other newly established Omicron variants or viruses from earlier in the pandemic. Questions linger about the ability of the XBB variant to evade vaccines, including recently administered boosters, and what kinds of sicknesses it may prompt this winter, explains Richard Martinello, M.D., the medical director of infection prevention at Yale New Haven Health System.
"One question is how readily it is transmitted between persons. Another is how it may be able to escape immunity, people's natural immunity or perhaps immunity against vaccines," says Dr. Martinello. "Because with the mutations we see in this strain, we're just concerned it may be able to escape or push through the immunity we already have — if that does prove to be true, that gives further evidence to suggest that, just like the flu vaccine, we may need periodic updates to our COVID vaccinations."
What exactly is the XBB variant?
Having first been confirmed in India over the summer, scientists know that the XBB variant is a combination of earlier Omicron subvariants — BA.2, in particular, says Shira Doron, M.D., infectious disease physician and epidemiologist at Boston's Tufts Medical Center. Additionally, a forthcoming study in China suggests that XBB strains are "the most antibody-evasive strain tested, far exceeding BA.5" and indicates that researchers believe that earned immunity wouldn't provide the same level of protection granted against previous versions of the virus.
"XBB doesn't appear to be more virulent or lethal at this time," Dr. Doron tells Good Housekeeping. "It has a 'growth advantage' over strains that were circulating in Singapore [in October], likely due to either increased contagiousness, increased ability to evade immunity due to mutations, or a combination of the two."
A heightened reason for concern over the XBB variant, in particular, is that its unique spike gene structure may be best poised to evade immunity granted by vaccines, Dr. Martinello adds. The same concerns exist for the effectiveness of monoclonal antibody treatments, including drugs like Evusheld that are given to at-risk, immunocompromised Americans who rely on extra protection to avoid infection.
More research will be required to determine the severity of disease caused by XBB infections — both for those who have recently recovered from a COVID-19 illness and those who are up-to-date on vaccinations. For now, experts like Dr. Martinello say officials are modeling potential outcomes based on earlier Omicron subvariants.
"The way a variant behaves in one country simply cannot be used to predict how it will behave in another," adds Dr. Doron. "There are too many differences between countries — levels of immunity that differ based on number and timing of infections, uptake of vaccination, types of vaccines, and even the underlying age and health of the population. That being said, we are always preparing for the possibility of future surges."
Potential XBB variant symptoms:
There isn't currently data to suggest that the XBB variant causes different symptoms from earlier strains of SARS-CoV-2, or triggers a specific subset of symptoms in average cases. Dr. Martinello suggests that there may be a more common immune response noted in due time, especially as more Americans receive their updated bivalent booster this fall, which may alter how immune systems respond to a future infection. "That immunity modifies how — if we do get infected again, or have been infected with COVID recently — we experience clinical symptoms that we have from COVID," he explains.
The most accurate way to tell if you're experiencing an XBB variant infection is to get tested. Since no two COVID-19 cases prompt the same kinds of symptoms with similar severity, current cases that may be triggered by XBB and other Omicron subvariants may lead to any combination of known COVID-19 symptoms.
If you're currently experiencing two or more of the following symptoms at the same time (especially if they feel severe!), you should seek out a COVID-19 test ASAP. Below are common COVID-19 symptoms associated with many of the Omicron subvariants currently in circulation:
Fever and body chills
Chronic fatigue and widespread body aches
Shortness of breath or difficulty breathing
Respiratory congestion, including runny nose
New loss of taste or smell
Nausea or vomiting
Can vaccines protect against contagious XBB variant spread?
The reason why the XBB variant may be successfully spreading COVID-19 so quickly among impacted communities is that previous vaccines — those administered before new bivalent vaccines were introduced this fall — "are not very good at preventing infection by any Omicron strain," Dr. Doron explains.
"One particular concern is that the new vaccine targets BA.4 and BA.5 subvariants, and we know XBB is partially a spinoff of BA.2 — but it's not at all clear that would make a difference clinically," she adds.
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— CDC (@CDCgov) October 27, 2022
There is yet to be official data shared by CDC officials or any other health agency on how effective the newer bivalent vaccine is against XBB or any other Omicron subvariant to emerge this winter. But the good news is that all vaccines, especially the most recent booster available to a majority of Americans at this time, have proven highly successful at preventing severe disease and death, even from circulating variants.
Dr. Martinello adds that the immune response to a COVID-19 illness is more than just antibodies against SARS-CoV-2 virus. "We also have a cellular response, and it's actually an area of immunology that we're not as easily able to test for, as we are for antibodies," he explains. "We don't know yet how well our cellular immunity is going to be able to respond."
Staying up to date on vaccines is crucial at this point, as there is more than enough evidence to suggest that vaccines significantly reduce risk of serious illness, even if they don't always prevent infection. Plus, they dramatically mitigate long-term consequences, including long COVID and risk for serious cardiovascular complications like heart attack risk or respiratory blood clots, Dr. Martinello says.
"We can prevent this by getting vaccinated, by using masks and by keeping our distance from crowds as best as we can this winter," he advises.
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