A nationwide study from the U.S. CDC is the first to show that immunity against COVID-19 begins to wane significantly four months after receipt of the third dose of an mRNA vaccine (Pfizer or Moderna).
Waning immunity was observed during both the Delta and Omicron variant waves in similar fashion to how mRNA vaccine effectiveness wanes after a second dose. Until this study, little was known about durability of protection following three doses, especially during periods of Delta or Omicron predominance in the U.S.
“The mRNA vaccines, including the booster shot, are very effective, but effectiveness declines over time. Our findings suggest that additional doses may be necessary to maintain protection against COVID-19, especially for high-risk populations,” said study co-author Brian Dixon, Ph.D., MPA, Regenstrief Institute and Indiana University Richard M. Fairbanks School of Public Health director of public health informatics.