Health and Science

CDC director says high immunity in U.S. population provides some protection against omicron BA.2

Key Points
  • CDC Director Rochelle Walensky said high levels of immunity from vaccination, boosters and prior infection should provide some protection against the omicron BA.2 variant in the US.
  • BA.2 makes up a growing a proportion of variants in the U.S., but new infections are steady at the moment. Hospitalizations are at their lowest level since 2020.
  • BA.2 has caused major outbreaks in Europe and China.
Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky gives her opening statement during the Senate Health, Education, Labor and Pensions hearing on "Next Steps: The Road Ahead for the COVID-19 Response" on Capitol Hill in Washington, November 4, 2021.
Elizabeth Frantz | Reuters

CDC Director Rochelle Walensky on Tuesday said there is enough immunity in the U.S. population to provide some protection against the more contagious omicron BA.2 subvariant, which could help stave off another Covid wave that slams hospitals.

"The high level of immunity in the population from vaccines, boosters and previous infection will provide some level of protection against BA.2," Walensky said during a White House Covid briefing. White House chief medical advisor Dr. Anthony Fauci said last month that infections might rise due to BA.2, but he doesn't expect another surge.

BA.2 now represents 72% of circulating Covid variants in the U.S., according to the Centers for Disease Control and Prevention. It has rapidly displaced the earlier version of omicron, BA.1, that caused the massive wave of infection over the winter. At the beginning of February, BA.2 represented about 1% of Covid variants in the U.S.

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BA.2 is now the dominant Covid variant in every region of the country, with circulation the highest in the densely populated Northeast, a repeated epicenter of the pandemic in the U.S. BA.2 makes up more than 80% of circulating variants in New England, New York, New Jersey, Puerto Rico and the Virgin Islands, according to the CDC.

An estimated 95% of the U.S. population ages 16 and older had developed antibodies against the virus either through vaccination or infection as of December, according to a CDC survey of blood donor samples. However, simply having antibodies against the virus does not necessarily stop an infection. Omicron, with its many mutations, has an enhanced ability to infect both the vaccinated and people who were previously infected.

However, people who are vaccinated, boosted and those who recovered from a prior infection all have high levels of protection against hospitalization from BA.2, according to a study published by scientists in Qatar affiliated with Weill Cornell Medicine in Doha. The study has not undergone peer review.

The scientists found that people who received three Pfizer shots had the highest protection against hospitalization from BA.2 at 98%. People who received two Pfizer doses and those who recovered from a prior infection had similar levels of protection against hospitalization at 76% and 73% respectively. People who had two Pfizer doses and recovered from a breakthrough infection had 97% protection.

The data suggests that even if BA.2 fuels an increase in infections in the U.S., there might be enough immunity in the population to prevent a major outbreak of severe disease that overwhelms hospitals.

BA.2 is anywhere from 30% to 80% more transmissible than the earlier version of omicron, according to public health authorities in the U.K. and Denmark. Scientists in the U.K., South Africa and elsewhere have found that BA.2 generally does not make people more sick than BA.1, which was less severe than the delta variant.

BA.2 has fueled outbreaks in Europe, including in the United Kingdom and Germany. China is battling its worst wave since 2020, locking down major cities such as Shanghai.

However, Covid infections in the U.S. are steady right now even as BA.2 makes up a growing proportion of virus variants in circulation around the country. The U.S. reported an average of about 25,000 new infections on Monday, down 4% from the week prior, according to data from the CDC. However, new infections are likely underreported as many people use at-home tests that aren't captured by the data.

The number of people hospitalized with Covid has fallen to the lowest since 2020. More than 10,700 patients were hospitalized with the virus on Tuesday as a seven-day average, a 92% drop from the peak of the omicron wave in January, according to data from the Health and Human Services Department.

The CDC has adjusted its Covid guidance to focus more on hospitalizations as a measure of how severely the virus is impacting the country. More than 97% of the U.S. population lives in counties with low-to-moderate Covid levels, which means people there do not need to wear masks under the CDC's guidance.