Over the last two years, the virus has continued to mutate, which means vaccine makers are constantly working to create new formulations. The new omicron-specific booster targets the two omicron subvariants, BA.4 and BA.5, which are responsible for the majority of COVID cases.
What’s Different About the New Omicron Booster Shot?
This booster shot incorporates omicron BA.4 and BA.5 spike protein components. “The new bivalent boosters available in the US are based on both the spike protein of the original SARS-CoV-2 strain as well as that of Omicron sub-variants circulating in the US, specifically BA.4 and BA.5,” says Dr. Erica Johnson, MD, chair of the Infectious Disease Board at the American Board of Internal Medicine. “It works by inducing antibodies that can bind to this spike protein and prevent it from attaching to cells and causing infection.”
How a Bivalent Vaccine Activates an Immune Response
The new bivalent formulations help address the fact that immunity wanes over time after each vaccine dose by boosting the immune response, but the bivalent formulations also specifically address the issue of the omicron subvariants’ ability to partially escape the immune response induced by vaccinations based on the original strain of SARS-COV-2, Dr. Johnson explains. Developing antibodies specifically in response to the spike protein shared by the BA.4 and BA.5 subvariants broadens the immune response and makes it more effective in neutralizing the virus subvariants that are currently circulating.
How Protective Will the New Shots Be Against Infection?
While results are promising among study participants, we will get a more realistic picture as more people get the shot. In the data presented to the FDA, administration of bivalent vaccine boosters to study participants who had completed a primary series and booster with the monovalent vaccines based on the original strain resulted in higher levels of neutralizing antibodies to Omicron subvariants compared with the antibody response developed after the monovalent vaccines alone, Dr. Johnson states. But it will be important to see how these bivalent boosters perform in real-world situations as more people receive them. You get sick with COVID when the spike protein of SARS-CoV-2 binds to your cells and allows for the virus to spread. The way the COVID vaccine works is by giving your immune system the blueprint to make antibodies, which binds to spike protein on COVID. This binding of antibodies to the spike protein does not allow the virus to spread, and you are protected from getting infected with COVID, Dr. Mahdee Sobhanie, MD, an infectious diseases physician at The Ohio State University Wexner Medical Center, explains. Over time, the spike protein has undergone changes or mutations in its structure which have led to variants such as delta and omicron. These variants have the potential to evade our existing vaccines because the spike protein does not bind as tightly and neatly to the antibodies the original vaccine produced for us. Despite these variants and changes to the spike protein, the vaccine is still providing incredible protection against hospitalization, development of severe disease, and death, Dr. Sobhanie adds. However, because of these variants, an updated vaccine is needed that will provide better protection against infection and prevention of disease. In human clinical trials and laboratory studies, Pfizer and Moderna were able to demonstrate that a booster developed against BA.1 (an earlier Omicron variant) showed a strong immune response and longer protection than the original vaccine. Since BA.1 has been replaced by BA.4 and BA.5 the FDA authorized the BA.4 and BA.5 omicron-specific boosters. These new vaccines are called “bivalent” vaccines which include the original strain of the SARS-CoV-2 virus and the BA.4 and BA.5 variants.
Will This Booster Protect Against Future Variants?
It is possible that this broader immune response induced by the bivalent booster may be more effective in neutralizing virus as new variants of concern arise, Dr. Johnson explains. But ultimately we will have to wait and see how these boosters perform in the real world to the current circulating subvariants and also how they perform as new variants of concern arise. Dr. Sobhanie says time will tell. “Every time a new variant is discovered there are three questions I ask myself: Will our vaccines hold up, will the medications we have hold up (Paxlovid and monoclonal antibodies), and how transmissible is the new variant? Right now, we know that the original COVID vaccines have protected us against severe illness and death—but we still have around 400 to 450 people dying of COVID a day.” The timing is right for an updated COVID vaccine, and we will have to see how the virus evolves and how well we are protected with an emerging variant. The updating of vaccines to protect us against respiratory illness is nothing new. Every year there are mutations that change a component of influenza—which is why there is an updated influenza vaccine on a yearly basis, Dr. Sobhanie adds. Whether or not a yearly COVID vaccine is needed, similar to the influenza vaccine, remains to be seen. What is important is that you stay up to date on your vaccine series, and get the updated booster if you are eligible. Next up: Can Omicron Cause Long COVID? Doctors Explain Exactly What We Know
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Dr. Erica Johnson, MD, Chair of the Infectious Disease Board at the American Board of Internal MedicineDr. Mahdee Sobhanie, an infectious diseases physician at The Ohio State University Wexner Medical Center
