Third mRNA Dose May Boost Antibody Quantity, but Not Quality

By Reuters Staff

August 03, 2021

(Reuters) - Among fully vaccinated people who never had COVID-19, getting a third dose of an mRNA vaccine from Pfizer/BioNTech or Moderna would likely increase levels of antibodies, but not antibodies that are better able to neutralize new virus variants, Rockefeller University researchers reported on bioRxiv ahead of peer review.

They note that in COVID-19 survivors, the immune system's antibodies evolve during the first year, becoming more potent and better able to resist new variants.

In 32 volunteers who never had COVID-19, they found that antibodies induced by mRNA vaccines did evolve between the first and second shots. But five months later, vaccine-induced antibodies were "equivalent" to those seen after the second dose, with "little measurable improvement" in the antibodies' ability to neutralize a broad variety of new variants, said coauthor Michel Nussenzweig.

Therefore, he said, giving those individuals a third dose of the same vaccine would likely result in higher levels of antibodies that remain less effective against variants.

"At the moment, the vaccine remains protective against serious infection," Nussenzweig said. "Should we learn that efficacy is indeed waning for serious infection, which is not really the case to date," then a booster dose of "whatever is available" might become appropriate, he added.

Should an updated vaccine become available that protects against specific variants, "then that would be the choice," Nussenzweig said.

SOURCE: bioRxiv, online July 29, 2021.