Q&A on Omicron-Updated COVID-19 Boosters
Earlier this month, the U.S. began administering the first COVID-19 booster vaccines that have been updated to better match the latest circulating coronavirus strains.
Many scientists expect the revised boosters will be more effective than their predecessors, but whether that’s the case and to what degree remains unknown.
The new vaccines, from mRNA vaccine makers Pfizer/BioNTech and Moderna, are bivalent, meaning that along with the original version of the coronavirus, or SARS-CoV-2, they also specifically target the BA.4 and BA.5 omicron subvariants. At the end of August, the Centers for Disease Control and Prevention estimated that together the two subvariants accounted for more than 90% of new COVID-19 cases in the U.S.
The Food and Drug Administration authorized the retooled boosters on Aug. 31, and the CDC signed off on the shots the following day, after the agency’s vaccine advisory committee voted 13 to 1 to recommend both boosters.
The authorizations mark a shift in American COVID-19 vaccination policy. In what’s being called a “fall booster ‘reset,’” people will no longer count the number of vaccine doses they’ve received. Instead, the guidelines are simple: If you’ve had your primary series (one dose of J&J or two doses Pfizer/BioNTech, Moderna or Novavax) and it’s been at least two months since your last dose, then you’re eligible for one omicron-updated booster.
We’ll explain how the new vaccines are different and what experts are saying about them.
How are the updated shots different from the original ones?
The revised boosters are essentially identical to the original ones, except for a tweak to some of the mRNA included in the shots.
For both Pfizer/BioNTech and Moderna, half of the mRNA in the vaccine includes the instructions used in the earlier vaccines for cells to make the spike protein of the original coronavirus strain. The other half includes the instructions for making the spike protein of the BA.4 and BA.5 strains, which is the same in the two subvariants. The spike proteins trigger a protective immune response in the body.
The dual components are why the boosters are referred to as “bivalent.” For the same reason, you may hear the original vaccines being called “monovalent.”
As before, the new Pfizer/BioNTech booster contains a total of 30 micrograms of mRNA, matching the dosage of the primary
