Omicron's Evolution and the New Bivalent COVID-19 Booster – UC San Francisco

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A Q&A with Joel Ernst on the Protection Offered by the Latest Vaccines
By Jeff Norris
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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