A subvariant of Omicron, called BA.2, has been sweeping across Europe and Asia in recent weeks, raising questions about if and when it will cause a surge in the United States.
The subvariant, sometimes called "stealth Omicron," has been shown to spread more easily, leading some experts to warn that it could prolong the Omicron surge in the states. But multiple factors—including vaccination rates, people with immunity from prior COVID-19 infections, and evolving pandemic policies—make it difficult to predict whether the U.S. will see a spike in cases, similar to what happened with the Delta and Omicron variants.
"[In] every country, at this point, the pandemic is a little bit different," Gregory Schrank, MD, MPH, an infectious disease doctor at the University of Maryland Medical Center and assistant professor of medicine at the University of Maryland School of Medicine, told Health.com. However, even if the U.S. saw a sharp rise in case counts, BA.2 isn't likely to cause the sort of large-scale lockdowns seen with previous variants, Dr. Schrank said.
Below, everything we know about the spread of BA.2 and the potential for another wave of COVID-19 infections in the U.S.
The BA.2 Subvariant, Explained
In November 2021, scientists in Botswana and South Africa discovered a new variant of SARS-CoV-2, the virus that causes COVID-19. Named Omicron, the variant quickly spread to other parts of the world, including the U.S., where it caused a record-shattering rise in COVID-19 cases at the end of 2021 and beginning of 2022.
Omicron has three main subvariants, called BA.1, BA.1.1, and BA.2, according to the World Health Organization (WHO). The "original" subvariant, BA.1, as well as the highly similar BA.1.1, caused most of the initial Omicron surges, including the one in the U.S., the New York Times has reported.
But BA.2 has recently caused case counts to rise in Hong Kong, South Korea, the United Kingdom, France, and Germany, according to data from the New York Times. Though the Centers for Disease Control and Prevention (CDC) recently estimated that the majority of COVID-19 cases in the U.S. are now caused by BA.2, the U.S. hasn't yet seen the same sharp upward trend being observed in other parts of the world.
"There's upticks a little bit in New York and Boston," Monica Gandhi, MD, MPH, an infectious disease doctor and professor of medicine at the University of California San Francisco, told Health.com. "But it's simply not a wave."
BA.2 does not seem to cause more severe illness than BA.1, which causes milder disease than previous COVID-19 variants. But the WHO has said that BA.2 appears more transmissible than BA.1. Some researchers estimate it's about 30% more contagious, according to Dr. Schrank.
Avoiding a BA.2 Surge in the U.S.
Why the U.S. has (so far) been spared another surge in cases likely comes down to key differences between the U.S. and areas that have seen sharp upticks, experts said. According to Dr. Gandhi, one such difference is acquired immunity—meaning, the number of people who have already been infected with the original Omicron variant.
A preprint study out of Denmark suggested that it's rare to become infected with BA.2 after having BA.1. An estimated 75% of people in the U.S. were exposed to Omicron during the initial surge, the Associated Press has reported. Infection with BA.2 after BA.1 appears "not impossible, but it's quite hard to get it," Dr. Gandhi said. In South Africa, for instance, the first country to be hit hard by Omicron, BA.2 hasn't yet caused another surge in cases, possibly from acquired immunity.
Dr. Gandhi said the number of people in the U.S. with hybrid immunity—meaning, they've been infected with COVID-19 and have also received the vaccine—might also have something to do with why we haven't yet seen a BA.2 surge. She added that, in this sense, it might be helpful to compare the U.S. to Denmark, which also has high rates of vaccination and acquired immunity, and also hasn't seen a BA.2 wave.
The vaccination rate in the U.S. might also be a factor. For starters, the U.S. has a higher vaccination rate, especially among vulnerable people, than Hong Kong and China, Dr. Gandhi said.
According to the CDC, 77.1% of the US has received at least one dose, and 65.7% is fully vaccinated. As of early April, only around 60% of people over 80 in Hong Kong had received at least one dose, and that number was about 34% when Hong Kong's surge began in early February.
Also worth noting: The types of vaccines available in Hong Kong and China aren't as effective as the mRNA vaccines more commonly used in the U.S. In fact, they're "the least effective of all of our vaccines," Dr. Gandhi said. Two of these vaccines also require three initial doses to work, she added, meaning a third dose wouldn't count as a booster.
Policy differences are also impacting the current state of the pandemic in many places. In Hong Kong, China, and South Korea, harsh restrictions early on meant that relatively few people were exposed to the virus, Dr. Gandhi said. Since most people have never been infected, there is very little virus-acquired immunity, and vaccination rates are also lower, since, previously, there wasn't an urgent need to vaccinate people, she said.
"It would be analogous to us experiencing an Omicron wave in 2020, before we really had vaccines available to us," Dr. Schrank said.
Additionally, current events can impact COVID-19 waves, and might be helpful in explaining why certain populations are seeing a rise in BA.2 cases while others aren't. Some of the surges in Europe could currently or eventually be related to the war in Ukraine—and the resulting mass migration—Bernadette Bodin-Albala, PhD, MPH, director and founding dean of public health at University of California Irvine, told Health.com. "You have a lot of potential for variants or spread because you've got more vulnerable populations," she said. Only around 35% of Ukrainians have been vaccinated.
Another Lockdown Is Unlikely
Despite the fact that the U.S. hasn't experienced a BA.2 surge, cases have been slowly increasing in some places, particularly in Northeastern states like New York and Massachusetts. It's plausible that current data might not show the extent to which COVID-19 is still spreading across the country, Dr. Gandhi said, since more people are taking advantage of at-home tests and not necessarily reporting their results. Previously used testing methods, such as PCR and rapid tests offered by health care providers and mobile testing stations, were reported to help track case counts.
Even so, Dr. Gandhi said it's unlikely that this could totally mask another wave of the virus. And Dr. Schrank said we can't rule out the possibility of a surge in the coming weeks or next month, specifically pointing to the surge of BA.2 in the U.K. "We generally have followed the pattern of being about one to two months behind the U.K. when they see a surge," he said.
Even if cases rise, though, we're unlikely to see the kind of large-scale restrictions we've seen in the past, like mask mandates or lockdowns, Bodin-Albala said. "I think we've moved away from mandates," she said.
There are several reasons for this, Dr. Schrank said, including that while we might see an increase in cases, research has shown that vaccinations, especially booster doses, do an excellent job of protecting people from severe disease and hospitalization.
And whether or not BA.2 causes a surge in the U.S., the pandemic isn't over. Another variant could still emerge, and when cases surge we will need to do the same things we've been doing to protect ourselves and the people around us, including wearing masks and making sure people are vaccinated and boosted, Bodin Albala said. "We will have another surge of COVID," she explained. "But I don't think it's BA.2."
The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.
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