If you got the Moderna or Pfizer COVID vaccine, chances are you're aware that you need two doses to reap the maximum protection from the vaccine. Those who got Moderna were told to wait 28 days between the two shots, and those who got Pfizer were instructed to wait 21 days ideally between their doses. But according to data from the Centers for Disease Control and Prevention (CDC), shared with CNN in late June, about one in 10 people are skipping out on their second COVID shot. Now that the Delta variant is spreading around the U.S. and cases are up in nearly all 50 states, you might be wondering if it's too late for you to get fully vaccinated, and now, there's more information on the vaccination timeline.
The timelines for the Modern and Pfizer vaccines—spread four and three weeks apart, respectively—were impressed upon the public by the CDC and other public health and medical professionals. The CDC advised everyone to get the "second dose as close as possible to the recommended interval. If the second dose is not administered within 42 days of the first dose, the series does not need to be restarted. Second doses inadvertently administered less than 21 days apart do not need to be repeated." But the truth is, that was simply because the manufactures didn't have much research beyond 42 days.
Experts now say the second dose boosts your immunity significantly, whether it's been weeks or months since your first shot. Han Kim, PhD, a professor of public health at Westminster College in Salt Lake City, called the 21 to 28 days between the COVID vaccine doses recommended by Pfizer and Moderna to be "a fairly arbitrary number." "It's never too late to get that second dose and up your protection levels," Kim told Desert News.
In the U.K., for example, the vaccine rollout plan was for everyone eligible to get their first shot before offering second doses, and research from that country on the Pfizer vaccine suggests waiting longer between doses may not only give you the same level of protection as it does for those who waited the recommended 21 days, but you may actually have more protection.
A study supported by the U.K. Coronavirus Immunology Consortium on 175 people over the age of 80 compared the immune response between those given the second Pfizer vaccine at the suggested three-week interval versus those given their second dose at a 12-week interval. The results showed that those who waited the 12 weeks between shots had a 3.5-fold higher antibody response compared to those who got their second dose three weeks after the first. In a statement, the study's lead author Helen Parry, MSc, PhD, said: "Our study demonstrates that peak antibody responses after the second Pfizer vaccine are markedly enhanced in older people when this is delayed to 12 weeks."
Public health experts predict people have skipped out on their second vaccines for a wide variety of reasons—some are fearful of side effects being worse from the second dose, and others had trouble scheduling their second appointments, with personal and professional obligations getting in the way. But some may have skipped their second shots based on misinformation.
David Broniatowski, associate director for George Washington University's Institute for Data, Democracy&Politics, told The Washington Post that some people believe that if they've already had COVID, they just need one dose. The hypothesis came from earlier studies on the subject, which Broniatowski points to as the root of the confusion. "When you have those sorts of things, people start to rationalize, 'Well, maybe it is not necessary to get that second dose,' especially when they have other barriers or other concerns," he said.
Kim agrees, especially as the Delta variant is now the dominant strain, accounting for 58 percent of new infections, according to the CDC. "I also encourage folks who did have confirmed COVID-19 earlier on to go get vaccinated. There's more and more evidence that natural infection with the initial strain is not very protective against Delta," Kim told Desert News. "So the risk of breakthrough infection is very high."
A U.K. study, which was published in May but has not yet been peer-reviewed, found that, after one dose, the Pfizer vaccine was just 33 percent effective against the Delta variant in preventing symptomatic COVID. But after the second dose, that number jumped to 88 percent.
"It's clear how important the second dose is to secure the strongest possible protection against COVID-19 and its variants," former U.K. health and social care secretary Matt Hancock said in a statement about the study.
In short, Kim says, "Go get your second dose. The timeline isn't relevant. That second dose is critical for protection against Delta. One dose is just not enough."