Almost everyone who received the first dose of the two-dose COVID-19 vaccine received the second dose within the recommended window, according to new data from the Center for Disease Control and Prevention.
During the first two months of the United States’ COVID-19 vaccination campaign, about 12 million people received the first dose and were also scheduled for the second dose. The second dose should be administered three weeks after the first for the Pfizer / BioNTech vaccine and four weeks for the Modern vaccine (with a few days buffer on each side). In this group, 88% of people had their second chance on time.
About 9 percent of people who took their first injection between December 14 and February 14 have not yet received their second dose, but were still 42 days after their first dose. The CDC says that when a delay is inevitable, people can wait that long. Three percent of people were outside the 42-day window and missed the dose.
To look at these numbers in a different way, the CDC also looked at everyone who received a second dose during those two months to see how many people received it within the recommended period. More than 95 percent of people were on schedule. Just under 3 percent of people were late (but within the 42-day window) and 1.5 percent of people had their second injection earlier.
The large number of people receiving their second dose – and on time – is comforting, the CDC wrote in its report. The Pfizer / BioNTech and Moderna vaccines may have some protection with just one dose, but a single dose was not part of the clinical trials, and it is not clear how long this protection can last. The second injection boosts the immune system and gives people all the benefits of vaccines.
When COVID-19 vaccines were developed and authorized, experts were concerned with the challenges of a two-dose series. They were worried that they would have a hard time getting people back for a second shot. In other multidose vaccines, such as the HPV vaccine and the herpes zoster vaccine, there is a drop. About a quarter of people who get the first herpes vaccine do not get the second, and only about half of people finish a series of three-dose HPV vaccines.
Despite the low number of people missing a second dose, CDC director Rochelle Walensky said the agency still hopes to close even the small gap. “The CDC is working across the government and with state and local partners to identify and address barriers to obtaining both doses,” she said at a news conference today.
States and health organizations have high- and low-tech strategies to bring people back to the second correct dose. Many central state immunization records can notify doctors and patients when people should receive a second dose. The same can happen with electronic health records. Everyone who receives the COVID-19 vaccine also receives a card that informs them when the second dose should be applied and which vaccine they received.
CDC data shows that these methods appear to be working. It is consistent with anecdotal reports of immunizers. “I’m not hearing any major challenges in bringing people back,” said Claire Hannan, executive director of the Association of Immunization Managers The Verge in February.
However, the CDC noted in its report that the majority of people who received the COVID-19 vaccine during the first two months they were available were health professionals and residents of long-term care facilities because they were the first to be eligible. These groups may be more likely to stick to the schedule because they could be vaccinated where they work or live.
The CDC report also says that 90,484 people received the first dose of one vaccine and the second dose of another – 0.2 percent of the total. The agency said that the Pfizer / BioNTech and Moderna vaccines should not be mixed, except in the most exceptional circumstances, when a second dose of the same brand is not available.
More than 37 million people in the United States are now fully vaccinated, either through two doses of the Pfizer / BioNTech or Moderna vaccine or one dose of the Johnson & Johnson vaccine, which gives just one injection.