CDC Report: Most Individuals Complete 2-Dose COVID-19 Vaccine Series


The CDC reported data demonstrating high adherence to COVID-19 vaccine doses among recipients.


Most COVID-19 vaccine recipients complete the second dose of their series within the recommended interval, according to new findings published in the CDC’s Morbidity and Mortality Weekly Report.1

Among individuals who received a first dose of the vaccine, 88% had completed the series an 8.6% had not received the second dose, but were still within the allowable time interval to receive it. Among all 2-dose recipients, 95.6% received the second dose of their series within the recommended time interval.

The findings were based on 2 analyses of COVID-19 vaccine administration data conducted among individuals who initiated the vaccination series between December 14, 2020 and February 14, 2021, and whose doses were reported to CDC through February 20, 2021. A total of 40,157,900 individuals initiated the COVID-19 vaccination series during this time and had vaccine administration data reported to the CDC.

For the first analysis, investigators aimed to determine whether recipients of the first dose who had sufficient time to receive the second dose had completed the series. The second analysis evaluated whether individuals who received a second COVID-19 vaccine dose by February 14, 2021 received the dose during the recommended dosing interval.

Although the data are reassuring, the investigators noted that priority groups vaccinated during this time period were more likely to have received their doses at work or residence, “which might have facilitated adherence to the recommended schedule.” As vaccine eligibility broadens, adherence to the recommended dosing interval may decrease.

The investigators provided recommendations regarding deviations to the dosing interval:

  • Although the second dose should be administered as close to the recommended interval as possible, it may be administered up to 42 days after the first dose when a delay is unavoidable.
  • If the second dose is administered beyond the allowable interval, the series does not need to be restarted.
  • Providers should not administer the second dose before the recommended interval or hold or save doses for patients who have not returned up to 42 days after the first dose.
  • Providers should regularly assess missed second doses and repurpose those doses as first doses for eligible recipients.

The analysis also looked at demographic differences in completion status among vaccine recipients. According to the data, the lowest series completion rate (83.7%) and the highest prevalence of missing the second dose (5.1%) was among American Indian and Alaska Native individuals. Additionally, series completion rates among non-Hispanic individuals of multiple/other races (86.1%) and Hispanic individuals (87%) were lower than the rates among non-Hispanic Native Hawaiian or other Pacific Islander (90.3%) and non-Hispanic White (90.3%) individuals.

Regarding age differences in completion status, series completion was lowest among adult aged 65 years and older (87.2%). Adults in this age group also accounted for the lowest percentage of missed second doses (2.3%).

Although missed doses and second doses administered outside of the recommended interval were rare, the investigators emphasized that public health officials and providers should work to better understand the reasons for lack of adherence to COVID-19 vaccine doses. Scheduling follow-up visits during the initial scheduling or administration and sending reminder notices during and after the second-dose interval can help ensure adherence.

As the vaccine becomes more widely available, pharmacists will play a critical role in promoting uptake and adherence among the general population.


1. 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. Morbidity and Mortality Weekly Report. March 19, 2021. Doi: icon.

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