New COVID-19 booster has two-pronged approach


Dear Doctors: How important is it to get the new COVID-19 booster? My husband and I are in our mid-40s and in good health. We both got the Moderna vaccine when it first came out, and we got a booster, too. What’s in this new shot? Also, is it true that it’s a good idea to switch up vaccine brands?

Dear Reader: We think it’s important for everyone who is medically eligible to be fully vaccinated against COVID-19 and to remain up-to-date with boosters. And yes, this includes the new bivalent vaccine, which was authorized by the Food and Drug Administration at the end of August.

The latest data show that 90% of all new COVID-19 infections in the United States are now caused by omicron BA.5, the newest subvariant. That speaks to the fact that it is the most easily spread strain of the coronavirus to date. The vaccine booster that you’re asking about includes components of the original coronavirus that causes COVID-19 and the omicron variant that has become the dominant strain. The boosters have proven to be effective at preventing serious disease as well as helping to prevent against initial infection.

Vaccines work by training the immune system to recognize one or more specific molecular characteristics of an invader. This allows the body to quickly mobilize its defenses and neutralize the threat. In the case of the coronavirus that causes COVID-19, the identifying marker was the distinctive spike protein on its outer surface.

The new bivalent booster trains the immune system to recognize the spike protein from the original virus. It also includes a “tutorial” that’s specific to the omicron variant. By targeting these two distinct spike proteins -- that’s the “bivalent” part of the vaccine -- the hope is that the new boosters will provide the person who receives the shot with more robust protection.

Elizabeth Ko, MD and Eve Glazier, MD
For the approximately 30% of people in the U.S. who remain unvaccinated, the guidance is to begin with the original two-dose series of the vaccine. You are considered to be up to date when you have completed the primary two-dose COVID-19 vaccine series and continue to receive the most recent booster dose that is recommended for you by CDC. This guidance varies by each person’s age, their specific COVID-19 vaccination history, the timing of their most recent dose and their medical history. You can find information about the coronavirus vaccines and boosters, as well as vaccination sites near you, at

You also asked about a mix-and-match approach to vaccines and boosters. This refers to the practice of switching between the Moderna and the Pfizer vaccines. There is reliable evidence that this practice may lead to enhanced immunity. People produce antibody responses from all three booster vaccines, no matter which vaccine they have originally received. But studies show that a subsequent dose of a different vaccine causes similar or higher antibody responses than a booster of the same vaccine.

Based on data from several studies into this approach, the FDA has authorized the use of mix-and-match doses for currently available COVID-19 vaccines.

(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)