Nearly nine out of 10 Americans who received the first dose of the Covid-19 two-dose vaccine completed the regimen, and most people who received two doses received them within the recommended timescales, federal health officials said on Monday.
The analyzes, carried out by researchers at the Centers for Disease Control and Prevention, included data on tens of millions of Americans who received the Moderna or Pfizer-BioNTech vaccines between mid-December and mid-February.
The percentage of people who completed the regimes varied markedly by jurisdiction and across demographic groups, however. Federal health officials have asked local vaccinators to take steps to ensure everyone returns, including scheduling a return visit when giving the first injection, sending reminders and rescheduling missed or canceled appointments.
Although the data was “reassuring” overall, the CDC researchers said, the first groups that received the vaccine in the United States – health professionals and long-term residents – had easy access to the second dose, since they were likely to would have been vaccinated at the place of work or residence.
As vaccines are offered to broader groups of people, scientists warned, the percentage of total vaccinations could fall.
People are not considered fully vaccinated against the coronavirus until two weeks after receiving the second injection of the two-dose regimen (or two weeks after receiving the single dose vaccine from Johnson & Johnson).
CDC researchers looked at about 40.5 million Americans who were vaccinated between December 14, 2020 and February 14, 2021.
In one analysis, they reviewed the records of 12.4 million people who received the first dose of a two-dose vaccine regimen and had enough time to receive the second dose. About 88 percent completed the series, while 8.6 percent were still within the allowed range – 42 days – to receive the second dose. But 3.4 percent missed that window. (The recommended interval between doses is 21 days for the Pfizer-BioNTech vaccine and 28 days for Moderna).
Americans most likely to miss a second dose vary by location. Among vaccine recipients for whom race and ethnicity information was known, the lowest completion rates occurred among Native Americans or Alaskan Natives.
A second analysis of 14.2 million people who completed the full regimen found that 95.6% received the second dose within the recommended period, although again the figures vary by community.
The study authors urged providers and public health professionals to encourage Americans to return to second doses and to emphasize the importance of complete vaccination. CDC officials also called for vaccinators to work to understand what prevents people from completing the series and whether access to or lack of confidence in vaccines is playing a role.