(HealthDay News) — 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 US Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Jennifer L. Kriss, PhD, from the CDC COVID-19 Response Team, and colleagues conducted 2 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% 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% had not received the second dose but remained within the allowable interval and 3.4% had missed the second dose. The percentage who missed the second dose varied by jurisdiction, from 0.0 to 9.1%, and among demographic groups. In the second analysis, 95.6% 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%.

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“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.


Kriss JL, Reynolds LE, Wang A, et al. COVID-19 Vaccine Second-Dose Completion and Interval Between First and Second Doses Among Vaccinated Persons — United States, December 14, 2020−February 14, 2021
Weekly / March 19, 2021 / 70(11);389-395.