What is Happening with Updates to COVID-19 Shots?

04 June, 2024

There have been several updates to COVID-19 vaccine recommendations since the initial rollout of COVID-19 vaccines. Keeping track of these changing recommendations and understanding why they changed may be challenging. Here we review background and updates regarding currently available COVID-19 vaccines, the populations recommended to receive them and what may happen in the future.

Why are there so many updates to COVID-19 shots?

There have been several recommended updates to the original two-dose primary series of COVID-19 vaccines. These updates are sometimes colloquially called “booster shots,” although strictly speaking, these shots are more accurately termed “updates” to the COVID-19 vaccination series. (“Booster shots” refer to shots specifically intended to “boost” an immune response that has already been “primed” by the primary shot or primary series, whereas these updated shots have the additional purpose of providing additional immunological protection against new variants.) Therefore, the preferred terminology is “updated shots” or being “up to date,” rather than “boosters” or “being boosted.”

Current COVID-19 vaccines are monovalent vaccines containing an XBB.1.5 spike antigen component, alone (CDC, October 2023). These vaccines are formulated to target currently circulating variants, specifically Omicron variant XBB.1.5 and related subvariants. Current vaccines no longer contain antigen against the original (ancestral) SARS-CoV-2 strain. This is primarily because the original SARS-CoV-2 strain no longer circulates in communities and newer variants have evolved to differ from this strain (CDC, October 2023; WHO, December 2023). Additionally, there is evidence suggesting that targeted monovalent vaccines can elicit higher neutralizing antibody titers against circulating SARS-CoV-2 variants as compared to use of bivalent vaccines (ancestral plus Omicron) (WHO, December 2023).

There are groups of individuals who may be at increased risk for severe disease with COVID-19, specifically those who simultaneously may not have as robust an immunological response to vaccination compared to other individuals. These groups include older adults 65 years of age or older, as well as individuals with immunocompromising conditions. It is particularly important for these groups to receive additional doses of updated vaccine (CDC, March 2024).

Plain-language summary: Updates to COVID-19 vaccines are needed because of changes that happen with the virus. The most updated COVID-19 vaccines better protect against currently variants, primarily from the Omicron variant of the virus. If you are an adult 65 years of age or older, or if you have an immunocompromising condition, you are recommended to receive additional doses of updated vaccine.


Will I need to get more COVID-19 shots in the future?

Yes. COVID-19 vaccines will continue to be updated in the future according to emerging strains of SARS-CoV-2 and the timing of seasonal epidemics of SARS-CoV-2. The SARS-CoV-2 virus has changed substantially since its emergence and continues to change in highly impactful ways that may represent immune escape and/or increases in virological fitness (Pulliam, March 2022; Cohen, July 2023). A plan to regularly update COVID-19 vaccines was suggested by FDA in January 2023.

This proposed updating schedule resembles, but does not duplicate, the regularly scheduled updates to yearly influenza vaccine; FDA has indicated the preferred schedule of review would occur in late spring/early summer, with updated vaccines scheduled to be available by fall each year. However, FDA has also indicated that additional updates would occur ad hoc as needed, if there were to be a sudden emergence of a highly transmissible strain and/or a strain exhibiting substantial immune escape. Decisions on how and when to update COVID-19 vaccines will be informed by global surveillance efforts including viral genomic analysis and viral neutralization data from vaccine studies (FDA, June 2023). FDA has also indicated that — to the extent possible — updated decision-making within the U.S. should be harmonized alongside international efforts for vaccine updates, including the World Health Organization and European Centre for Disease Control and Prevention. For example, it is expected that an updated vaccine formulation will be made available this fall, likely targeting the now globally dominant JN.1 Omicron subvariant.

Plain-language summary: Yes. COVID-19 vaccines will need to be updated on a regular schedule. It’s likely that updates will occur yearly, with new vaccines available in the fall of each year. The updates that are made to vaccines will depend on circulating variants and how well the current vaccines can protect against those circulating variants.


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