Most people complete two-dose COVID-19 vaccination series

Most people who receive the first Pfizer-BioNTech or Moderna COVID-19 vaccine complete the series, almost always within the recommended interval, according to research published in the March 15 early-release issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Jennifer L. Kriss, Ph.D., from the CDC COVID-19 Response Team, and colleagues conducted two analyses of COVID-19 vaccine administration data among persons who initiated vaccination during Dec. 14, 2020, to Feb. 14, 2021. The first analysis examined whether persons who received a first dose and had sufficient time to receive the second dose had received the second dose. The second analysis was conducted among those who received a second dose by Feb. 14, 2021, to examine whether that dose was received during the recommended dosing interval (17 to 25 days for Pfizer-BioNTech; 24 to 32 days for Moderna).

The researchers found that in the first analysis, 88.0 percent of the 12,496,258 persons who received the first vaccine dose and for whom sufficient time had elapsed to receive the second dose had completed the series; 8.6 percent had not received the second dose but remained within the allowable interval and 3.4 percent had missed the second dose. The percentage who missed the second dose varied by jurisdiction, from 0.0 to 9.1 percent, and among demographic groups. In the second analysis, 95.6 percent of the 14,205,768 persons who received a second dose did so within the recommended interval, with percentages varying by jurisdiction from 79.0 to 99.9 percent.

"Public health officials and providers should work to better understand the reasons for lack of completion of the COVID-19 vaccination series and early and delayed intervals," the authors write.