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Nearly three years into the SARS-COV-2 pandemic, we’re still fighting it off.
Over time, variants have evolved that are more fit to escape immunity from past infection or vaccination. This has necessitated updates to the COVID-19 boosters that better match the components of the vaccine with the circulating omicron subvariants. The updated bivalent COVID-19 boosters are now available.
Read on for common Q&As about the booster.
How well did the original vaccines work to protect against COVID-19?
The original Pfizer-BioNTech and Moderna mRNA vaccines targeted the spike protein from the ancestral strain of SARS-COV-2. Vaccine efficacy was 95% against the early variants that circulated in 2020 and early 2021. The effectiveness declined slightly with the emergence of the delta variant in the summer of 2021.
But a major shift change occurred at the end of 2021 with the emergence of the omicron BA1 variant. The omicron variants contain more than 30 mutations on the spike protein, 15 on the receptor-binding domain.
The cross protection against omicron BA1 afforded from past vaccination was still better than being unvaccinated: 30% higher effectiveness without a booster, 80% higher with a booster, and more than 90% vaccine effectiveness when counting COVID-19 hospitalizations only.
Since February 2022, omicron subvariants have emerged, most recently the BA4 and BA5 variants. BA4 and BA5 are significantly more immune evasive, even against past infection with omicron BA1. BA4 and BA5 have been circulating as the predominant variants throughout the summer of 2022.
How did the monovalent (original) boosters improve protection?
After a COVID-19 booster, the spike protein is reintroduced to immune cells, leading to an increased repertoire of antibodies that are higher quality and attach better to targets on the spike protein. Even though the original vaccine only partially matched the omicron variant, a booster of the original vaccine improved vaccine effectiveness to 80% against the omicron variant. But the level of protection diminishes after several months. A second booster was found to restore protection for older adults and have a profound effect on reducing COVID-19 hospitalizations.
How is the updated bivalent booster expected to work better?
Instead of just relying on the cross protection from what is still in common between the original variant and the omicron variant, the updated bivalent boosters also provide direct protection against a host of new antigens unique to the BA4 and BA5 spike protein.
The updated boosters made by Pfizer BioNTech and Moderna contain the same mRNA as the original vaccine as well as mRNA shared by the BA4 and BA5 spike protein. With BA4 and BA5 currently circulating, there is a direct match with the updated bivalent booster and the currently circulating virus. With ongoing evolution of omicron subvariants, the updated bivalent booster may still be a better match to other omicron subvariants as well as previous variants, than the monovalent vaccine.
What is the science on the efficacy of updated bivalent boosters?
Shortly after the omicron BA1 variant emerged, both Moderna and Pfizer BioNTech embarked on studies using different combinations of mRNA variant vaccines to determine which had the best immune response. It was found that a bivalent booster using the original mRNA, combined with mRNA for the BA1 variant given, elicited significantly higher levels of neutralizing antibodies against BA1 than the monovalent booster. But by the time the studies had completed, BA4 and BA 5 were already predominant.
On June 30, 2022, the Food and Drug Administration (FDA) advised Moderna and Pfizer to manufacture a bivalent vaccine containing the original component and BA4/BA5, rather than BA1, while at the same time advancing clinical trials on vaccine efficacy. On Aug. 31, 2022, the FDA issued an emergency use authorization for the bivalent boosters made by Moderna for adults ages 18 and older and by Pfizer BioNTech for adults and children ages 12 and older. The Centers for Disease Control and Prevention (CDC) issued recommendations on Sept. 1, 2022.
The original COVID-19 vaccine will still be used for the primary series, and for boosters in children ages 5-11 years, but will no longer be used as a booster for those ages 12 years and older.
Will the updated bivalent booster be a yearly booster, just like the influenza vaccines?
Influenza vaccines are updated yearly to match recent strains, and then administered in the fall to provide immune protection through the winter months while influenza is circulating.
The updated bivalent COVID-19 boosters given now should provide maximal protection through the fall and winter months, when there may be a higher level of virus transmission. Yearly updated COVID-19 vaccines may be needed to restore waning immunity and to match the vaccine components to circulating variants.
Whether older adults or other high-risk individuals may need boosters more than yearly depends on what is learned about the durability of protection against severe outcomes. If there is further drift of omicron subvariants, the updated bivalent booster may still provide adequate cross protection until the next yearly update. In the unlikely event of another major shift change, away from omicron, a more urgent update would be needed.
Who can get the updated bivalent boosters?
Adults and children ages 12 years and older can get an updated (bivalent) COVID-19 booster if the following eligibility criteria is met:
Even people who have received two previous monovalent boosters are eligible to receive the updated bivalent booster, if it has been more than two months since their last shot.
If I am vaccinated and had COVID-19 recently, how long should I wait to get an updated bivalent booster?
There is no minimum waiting period to get a booster after your infection resolves. Hybrid immunity from a combination of vaccination and infection makes the chance of re-infection low for the first few months. But after three months the risk of re-infection starts to increase due to a combination of waning immunity and evolving immune evasive variants. Waiting a few months may give you a more robust immune response as well as better protection into the spring and summer months, when immunity may be waning.
When will children under the age of 12 years be eligible for an updated booster?
Children ages 6 months to 4 years can still receive the 3-dose Pfizer-BioNTech or 2-dose Moderna COVID-19 vaccine. Children ages 5-11 years can also still receive the original monovalent booster. It is critical to get the third dose or a booster to get a high level of vaccine effectiveness. Ongoing studies will inform how soon the boosters can be updated for children, too.
To stay up-to-date with COVID-19 vaccines, people need to have received the primary vaccine series and an updated booster.
Edward-Elmhurst Health has COVID-19 vaccine appointments available to ages 6 months and older, including booster doses for those eligible. It is easy to schedule a vaccine appointment. Schedule your COVID-19 vaccine now.
Learn more about the COVID-19 vaccine.
The information in this article may change at any time due to the changing landscape of this pandemic. Read more about COVID-19.
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