Omicron’s Evolution and the New Bivalent COVID-19 Booster

Last month new booster vaccines made by Moderna and Pfizer became available. They are called “bivalent,” because they protect against currently circulating Omicron variants as well as earlier strains of the SARS-CoV-2 virus that causes COVID-19. Boosters reduce the likelihood of becoming infected with Omicron, and they also reduce the likelihood of hospitalization and death should one become infected despite vaccination.

To learn more about the new booster vaccines and the prospects for gaining the upper hand against COVID-19, we spoke to Joel Ernst, MD, a UCSF professor of medicine whose research aims to understand how pathogens evade the immune system.

Which COVID-19 virus variants are the new vaccines designed to fight?

Each vaccine has a fifty-fifty mix of the virus’s spike protein from the original Wuhan strain of the virus that was used for the earlier vaccines and a spike protein segment from the Omicron BA4 and BA5 variants responsible for the most recent surge, and for most new U.S. cases today.

How soon after vaccination does the booster offer its strongest protection, and how long will protection last?

The booster ramps up to a high level of protection in about a week – faster than a first-vaccine dose – and surely within two weeks. We’re not sure how long the new booster will be protective, but it will likely act like earlier boosters, providing optimal protection for two-to-four months, good protection for four-to-six months, and less protection, but still some, after six months.

Should people who received a monovalent booster recently wait awhile before receiving the bivalent vaccine designed to also fight these Omicron variants?

It’s appropriate to wait at least two months from the time of the previous booster, but many people may choose to wait four months, as a previous booster is likely to offer sufficient protection to greatly reduce risk of severe infection for four months.

Vaccines and Long COVID

Do we know anything about the added protection provided by the bivalent booster in terms of risks for infection, transmission, serious disease or long COVID?

It’s too early to know about any of those types of protection. What’s known so far is that the new bivalent boosters increase the immune system’s antibody responses to the BA4 and BA5 Omicron variants far beyond responses seen with the earlier monovalent vaccine. Even though we don’t have data on infection and serious disease, we have reason to believe from the antibody responses that the new vaccine will provide greater protection against these newer variants.

If I was infected with an Omicron variant already, should I still get this new booster?

Yes, some people have become reinfected. However, it’s recommended to wait two months since the last symptomatic infection before getting a booster. Some protective COVID-virus-targeting T cells and antibody-producing B cells remain after infection ends, but they need time to readjust and reset their metabolism before they can respond optimally to a booster vaccine.

New Omicron Variants

Another highly transmissible mutant Omicron strain of COVID-19, called BA2.75.2, is rapidly becoming dominant in India, and has shown up in several other countries around the globe. Do you think this strain poses a threat for another pandemic surge in the United States or elsewhere? Is it known how likely that strain is to cause serious disease, and should we expect the bivalent vaccine to offer any protection?

The answers to all those questions are still outstanding. I am concerned about it. But there have been other variants that have emerged and spread widely in one country or another and then never made it very far. There’s reason to believe that the new vaccine will be more effective than the old vaccine against that new strain. It’s been hard to accurately predict which variants will spread, but from a public health perspective, it’s important to conduct surveillance and to genetically sequence the virus to detect the arrival of new variants and to track changes in variant prevalence.

No human data for the new Omicron vaccines were presented for review prior to approval. Do you have any concerns that potential risks of vaccination might be underestimated?

I don’t think there is any reason to think that these new vaccines will pose any risks beyond what we have already seen with the original vaccines. The total dose of RNA in the new vaccines is the same as in the earlier vaccines. Serious side effects are extremely rare, and benefits exceed risks.

What about the risk of myocarditis?

There have been quite a few studies with the earlier vaccines, which indicate that there is one case of myocarditis per 100,000 to 200,000 people vaccinated. The risk is small, but not zero. The risk is consistently higher in males under age 40. Except in exceedingly rare cases, vaccine-associated myocarditis cases have been transient – people recover. Studies indicate that incidence of myocarditis among people infected with SARS-CoV-2 is much higher than incidence due to vaccination.

Booster and Flu Shots Together

If I get my Omicron booster right away, should I get a flu shot at the same time, or is there a better time to get the flu shot to avoid interactions and to obtain maximum protection during flu season?

It’s fine to save a trip and get both at the same time. If you anticipate being uncomfortable with symptoms that arise as your immune system responds to either of the vaccinations, you might want to get them at different times. Maybe it’s on the early side, but September or October is not too soon for a flu shot. We never know for sure when the flu season is going to hit.

Will COVID ever go away?

My answer is that I am optimistic that the pandemic is going to recede into the background, even if it is unlikely to go away. I think the virus will mutate to a point where it doesn’t make people as sick as it did early on, and our immunity will continue to increase.