Most people who have received a first dose of Covid-19 vaccine are getting their second dose on time, according to early data from the US Centers for Disease Control and Prevention.
But CDC researchers warn that the initial groups prioritized to receive the vaccine – health care workers and long-term care facility residents – have had easy access to a second dose through their workplace or residence.
“As priority groups broaden, adherence to the recommended dosing interval might decrease,” the researchers wrote in their report published on Monday.
For the Pfizer/BioNTech and Moderna vaccines, it is recommended for second doses to be administered 21 and 28 days later, respectively, but the researchers noted in their report that up to 42 days between doses is permissible if needed.
The report includes data on more than 37 million people who received at least their first dose of Covid-19 vaccine between Dec. 14 and Feb. 14.
The researchers analyzed the data, taking a close look at when the first dose was received, whether a second dose was received and whether that second dose was received on time. The data came from 58 jurisdictions across the United States.
The researchers found that among those where enough time had gone by to receive a second dose, 88% of people had completed their second dose, 8.6% had not but there was still enough time to receive their second dose, and 3.4% had missed the second dose completely – meaning at least 42 days had gone by since receiving their first dose.
Among those in the data who had received both doses, the researchers found that 95.6% received their second dose within the recommended time interval.
The researchers noted that several winter weather events led to distribution challenges and vaccination clinics canceling appointments during the study, and more research is needed to examine the completion of second doses over a longer period of time.
“Continued monitoring of series completion status across jurisdictions and by demographic characteristics is important to ensure equity in vaccine administration and vaccination coverage, especially as vaccination efforts expand to additional population groups,” the researchers wrote.