Press "Enter" to skip to content

New booster for the BA.4 and BA.5 variants: Dr. Petri answers your questions on FDA authorization

University of Virginia immunologist and COVID-19 researcher Dr. William Petri continues to answer reader questions about COVID-19. Send your questions to Lynne Anderson at, and she will forward them to Dr. Petri.

What does the new booster vaccine for COVID-19 do?

The booster when available later this month will provide better immunity against the current omicron subvariants BA.4 and BA.5. All of our current vaccines use the spike glycoprotein from the original SARS-CoV-2 virus from Wuhan, China. The new booster has the Wuhan strain in it but also has the mRNA sequence for the current omicron subvariants BA.4 and BA.5 that are causing more than 90% of COVID-19 infections in the US. It will thus be what is called a bivalent vaccine, giving another boost of the original vaccine while promoting better protection against the subvariants of omicron currently in circulation.

Why bother? Isn’t omicron much milder than earlier variants?

Actually if you end up hospitalized with omicron, the chances of dying are a bit higher than with the earlier delta variant. But over all fewer people are getting hospitalized with omicron, so daily deaths in the U.S. are hovering around 500. The reason that fewer people are getting severe COVID-19 today has less to do with the virus and more to do with the fact that currently everyone in the U.S. has some degree of immunity either from vaccination and/or prior omicron infection. However, we know that immunity against the coronaviruses is not long-lasting — months and not years. The reason therefore to be vaccinated with the bivalent booster is to maintain that high level of immunity so as not to end up vulnerable to a severe infection.

When will it be ready?

The FDA authorized the bivalent vaccine today. The next steps are a review by the Advisory Committee on Immunization Practices (ACIP), an panel of medical and public health professionals who are independent of government and the pharmaceutical industry, to make their recommendation. Assuming that ACIP approves, then the final step will be for the CDC to review and approve. Assuming this all happens this week, it is likely that the booster will be available in Charlottesville as early as next week.

Who will be eligible?

The CDC ultimately will decide who is eligible, but the expectation is that everyone ages 12 years and older, and who are at least 2 months out from the last booster, will be able to immediately receive the new bivalent booster.

Why did the FDA approve the new bivalent booster without requiring human clinical trials?

The bivalent boosters use the same mRNA vaccine technology as the original vaccines which have proven safe over the millions of doses administered. All that is different is that the sequence of the spike glycoprotein mRNA, which had been the Wuhan strain, now includes that of the BA4 and BA5 omicron virus subvariants. This approach, of not requiring new human clinical trials when all that has changed in the vaccine is the viral variant, is used routinely every year for the new flu booster vaccine. There have been studies of the new booster in mice, which have demonstrated 20-fold better protection against BA4 and BA5 than the original vaccine.

Is it going to knock people on their posteriors?

The new vaccine should behave the same as the old vaccine as far as side effects, so if you had flu-like symptoms for example with the old booster, you may have them again with the new booster.

Will this work for future variants?

It will be much better for omicron in general than the original vaccine, but not perfect, as already there is a new omicron subvariant called BA4.6, due to a mutation in the spike glycoprotein. It has the ability to partially escape immunity from omicron. It will likely also be limited in the time that it will provide the best levels of protection, likely less than a year, similar to the old booster. Fortunately, protection against the most severe disease, leading to hospitalization, is stronger than protection against merely being infected. This is a major reason to receive the new booster when it becomes available later this month.


Be First to Comment

    Leave a Reply

    Your email address will not be published. Required fields are marked *