On Sept. 12, 2023, the Centers for Disease Control and Prevention recommended the newly formulated COVID-19 vaccines for all Americans ages 6 months and up, hours after its expert advisory committee voted 13 to 1 in favor of recommending the vaccines.
The CDC’s broad recommendation comes one day after the Food and Drug Administration approved Moderna’s and Pfizer’s updated mRNA vaccines that target a previously dominant variant of the omicron family called XBB.1.5. The updated shots will be available to the public within days.
The Conversation asked Prakash Nagarkatti and Mitzi Nagarkatti, a husband-and-wife team of immunologists from the University of South Carolina, to weigh in on how the new vaccines might stand up against the latest COVID-19 variants that are swirling across the globe.
1. How Are the New Vaccines Different From the Previous?
When the first vaccine against COVID-19 was rolled out in December 2020, it was designed as a monovalent vaccine, meaning that it was formulated against only the original SARS-CoV-2 virus. That vaccine, as well as the updated ones, target the spike protein, which the virus uses to infect our cells and cause the disease.
That design made sense before the virus began mutating into a complex family tree of variants and sublineages. But as the virus structure shifted over time, the antibodies produced in response to the original vaccine became less effective against the new variants.
This necessitated the development in 2022 of new “bivalent” vaccines that targeted both the original strain of SARS‑CoV‑2 and new viral variants such as the omicron BA.4 and BA.5 lineages that were dominant in mid-2022.
But, not surprisingly, new variants of the virus continued to emerge.
In June 2023, the FDA asked vaccine developers to formulate new fall shots to target the then-dominant XBB.1.5 subvariant.
The FDA approved that monovalent mRNA-based vaccine based on the overall efficacy data presented by the vaccine manufacturers.
Unfortunately, XBB.1.5 is no longer the dominant strain in the U.S.; it has been displaced by other variants from the XBB lineage, thereby raising concerns about the potential efficacy of the new shot. As of mid-September,
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