The federal Food and Drug Administration has authorized updated COVID-19 boosters that are a better match for the current circulating coronavirus strains. The new boosters from Pfizer-BioNTech and Moderna are now available at local clinics and pharmacies including CVS and Walgreens.
The updated bivalent, or two-target, boosters contain genetic instructions for spike proteins from both the original SARS-CoV-2 variant and the newer BA.4 and BA.5 omicron variants. BA.5, which emerged in April, is now responsible for most COVID cases worldwide, including the Bay Area.
"The updated COVID-19 boosters are formulated to better protect against the most recently circulating COVID-19 variant. They can help restore protection that has waned since previous vaccination and were designed to provide broader protection against newer variants," said Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, which recently updated its vaccine recommendations to include the new boosters.
At a September 6 media briefing, Biden administration officials suggested that after this round of boosters, updated COVID vaccines might be administered annually, like flu shots.
"It is becoming increasingly clear that, looking forward with the COVID-19 pandemic, in the absence of a dramatically different variant, we likely are moving toward a path with a vaccination cadence similar to that of the annual influenza vaccine, with annual, updated COVID-19 shots matched to the currently circulating strains for most of the population," said National Institute of Allergy and Infectious Diseases director and White House chief medical adviser Dr. Anthony Fauci.
The Pfizer-BioNTech bivalent booster is now available for people ages 12 and older while the Moderna booster is available for those ages 18 and up. The new boosters contain a smaller amount of mRNA than the original vaccines, and they are not approved for use as an initial vaccine series.
People can get the new boosters at least two months after their last vaccine dose, and the CDC recommends waiting at least three months after a bout of COVID. But some experts think it's better to wait around six months after a previous vaccine dose or infection to give the immune system more time to work.
Vaccines temporarily raise antibody levels, but they also stimulate memory B-cell and T-cell responses, which provide longer-lasting protection against severe disease. A large proportion of the population came down with COVID during the winter surge, and post-infection natural immunity also offers temporary protection.
"While your antibodies are maturing after a previous vaccine or infection, they should be allowed to have that time without being exposed to another booster," Dr. Monica Gandhi of UCSF told the Bay Area Reporter. "Our booster strategy should recognize this existing immunity and seek to build upon it in a manner that prolongs protection throughout the winter."
Vaccine development
One advantage of the mRNA technology is that genetic code for new variants can be plugged into the same platform, enabling more rapid development of updated vaccines as the virus evolves. Pfizer-BioNTech and Moderna first developed bivalent boosters targeting the BA.1 omicron variant, which was responsible for the winter surge, but the FDA decided it would be better to target the newer BA.4 and BA.5 variants.
Although the safety and immunogenicity (ability to stimulate antibody production) of the BA.1 bivalent boosters were tested in clinical trials, the new BA.4/BA.5 boosters were authorized based on studies in mice. This is how annual flu vaccines are developed. Waiting for the results of human trials could give new variants time to take over in the meantime.
Since they use the same mRNA platform, the BA.4/BA.5 boosters are not expected to present any new safety concerns. The side effects are expected to be similar to those of the original COVID vaccines, namely temporary soreness at the injection site and flu-like symptoms. Myocarditis (heart muscle inflammation) is a rare adverse event most often seen in young men.
"The FDA has been planning for the possibility that the composition of the COVID-19 vaccines would need to be modified to address circulating variants," Dr. Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, said in a statement. "The public can be assured that a great deal of care has been taken by the FDA to ensure that these bivalent COVID-19 vaccines meet our rigorous safety, effectiveness and manufacturing quality standards for emergency use authorization."
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