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What to Know about the ‘Stealth’ Omicron Subvariant

U.S. COVID-19 rates are falling as subvariant gains larger share of cases

March 16, 2022

In Pennsylvania and across the U.S., COVID-19 cases have plunged from the winter peak, but the Omicron “stealth” subvariant has emerged as the latest development to watch.

During the past few months, virologists and global health leaders have been monitoring the spread of the Omicron subvariant, BA.2, which appears to be more transmissible and has been linked to rising case counts in other parts of the world.

The appearance of the subvariant comes as daily case counts have dipped below 1,000 in Pennsylvania for the first time since last summer. Currently, BA.2 accounts for about 20 percent of Omicron cases in Region 3, which includes Pennsylvania, and nearly 40 percent of cases in other parts of the northeast.

The next two to three weeks will be very telling, Lindsey R. Baden, MD, professor of medicine, Harvard Medical School, said during a recent webinar from the Infectious Diseases Society of America.

Here are five things to know about the subvariant:

The ‘Stealth’ nickname:  BA.2 was given the “stealth” nickname because it has mutations that made it harder to distinguish from the Delta variant using PCR tests, according to the American Medical Association

Proportion:  The U.S. has seen a slower rise of BA.2 than other countries. The subvariant accounts for 23.1 percent of U.S. cases, up from about 10 percent a week ago, according to the Centers for Disease Control and Prevention

Global cases:  Virologists are watching closely as cases start to rise again in nearly half of European countries and China. BA.2 has become the dominant sublineage in some of these countries

For perspective:  “Although the proportion of infections with BA.2 is increasing in the U.S., COVID-19 cases are now declining, so it is likely that absolute numbers of BA.2 infections are not increasing as quickly as they might seem from just looking at the proportion that are BA.2,” Debbie Dowell, MD, MPH, chief medical officer for CDC's COVID-19 Response, said during the Infectious Diseases Society of America webinar

Reinfection protection:  Early analysis indicates that infection from the original Omicron strain provides some degree of protection against reinfection for BA.2, Dowell said. One study indicated reinfection was mild overall, relatively rare, and occurred most often in younger, unvaccinated individuals

Dowell said the severity of the subvariant and vaccine protection against infection appear to be similar when comparing BA.2 to the original Omicron strain. Booster doses are important to address waning immunity from the vaccines, she noted.

HAP will continue to monitor the latest COVID-19 developments and provide updates to members and the general public. Additionally, HAP strongly encourages everyone who is eligible to stay up to date on their COVID-19 vaccines.

More information and vaccine appointments in your community are available online.