COVID-19 Monovalent Vaccines: An ACIP Recommendations Quiz

Terry Brenneman, MD

A lot of interesting information was presented at the September 12, 2023, meeting of the US Centers for Disease Control and Prevention’s (CDC) Advisory Committee on Immunization Practices (ACIP) on the new COVID-19 monovalent vaccines. You can review the slides for additional information. The new monovalent vaccine targeting the XBB.1.5 variant is now recommended for all Americans over the age of 6 months either as the primary series or as a booster. Last year's bivalent vaccine should no longer be given.

The COVID-19 virus, like the influenza virus, is constantly mutating with selective pressure to avoid the immune system's defenses including in persons previously infected or vaccinated. Multiple COVID-19 strains are circulating at all times. The CDC lists 31 different strains that account for 99.9% of current infections. Most of these differ from each other by only a few amino acid substitutions. In May 2023, approximately 50% of new cases were caused by the XBB.1.5 variant. As of August 2023, this number dropped to approximately 15%. How well will this new monovalent vaccine work against the new evolving strains? Details in the 2-question quiz below.