CDC: Waiting 8 Weeks Between COVID Vaccine Doses Reduces Risk of Myocarditis

Some people can space out the first and second doses of the Pfizer and Moderna COVID-19 mRNA vaccines for as long as eight weeks, according to new guidance released Tuesday, February 22, from the Centers for Disease Control and Prevention (CDC).

The guidance is especially aimed at people over the age of 12 and males between the ages of 12 to 39.

Original guidance from the CDC recommended that the second dose be administered three weeks after the first shot of the Pfizer vaccine and four weeks after the first shot of the Moderna vaccine.

The CDC said vaccines remain safe and effective even if people follow the originally recommended time interval, but extending the interval may reduce the rare risk of myocarditis, a type of heart muscle inflammation, particularly among certain groups.

“While absolute risk remains small, the relative risk for myocarditis is higher for males ages 12–39 years, and this risk might be reduced by extending the interval between the first and second dose,” the CDC stated. Some studies in people older than 12 have shown “the small risk of myocarditis associated with mRNA COVID-19 vaccines might be reduced and peak antibody responses and vaccine effectiveness may be increased with an interval longer than 4 weeks,” according to the CDC.

How Is the New Guidance Different?

According to the CDC, people older than 12 and young men who wait as long as eight weeks before getting their second COVID-19 vaccine dose can reduce the small risk of developing myocarditis.

Intervals longer than four weeks can also increase antibody response and vaccine effectiveness.

Lee Wetzler, MD, professor of medicine at Boston University School of Medicine, told Verywell while the new guidance does not apply to or change anything for people who are fully vaccinated, there is evidence that spreading out vaccine doses for longer can enhance immunity—a consideration for those who are not vaccinated yet or are waiting to get their second dose.

“Waiting six or eight weeks is not as big of a deal as it used to be when we were seeing so many people infected and getting sick,” he said. “In the midst of the pandemic, we were trying to raise immunity as quickly as possible. Even though there’s still disease around now, it appears we have a little more leeway and if we increase the interval, overall immunity seems to be enhanced.”

The CDC still recommends the three or four-week interval for people who are moderately or severely immunocompromised, adults 65 and older, and others who need rapid protection due to increased concern about community transmission or risk of severe disease. Officials added since there is no data available for children younger than 11, this group is still recommended to get the second Pfizer vaccine three weeks after the first dose.

Why Now?

As the COVID-19 pandemic continues, health experts and researchers are learning more information about how to control the spread of disease, how to keep people safe, and the best times for people to get vaccinated. Wetzler said by understanding how the virus works through research and studies, health authorities can recommend new guidance for people to follow.

“It’s like trying to fly an airplane while you’re building it,” Wetzler said. “We’re going to learn a lot more and we should never stop looking at this because this is not the last time we’re going to see something like this. We can apply it to the next time we have a pandemic.”

He added new recommendations including longer vaccine schedules will be beneficial for people who have yet to be vaccinated, including new generations, and it can bring guidance to existing communities if shots will be needed in the foreseeable future.

“New recommendations are not pointless in any respect,” he said. “Depending on what happens with epidemiology and immunity, I think the pandemic will be around for the rest of our lives. But whether we’re going to have to take the shot for the rest of our lives is unclear because we really don’t know the level of immunologic memory yet.”

Paul Auwaerter, MD, a professor of medicine at Johns Hopkins University, told Verywell in an email he believes additional vaccines may be needed for certain groups, such as those who are 65, to maintain sufficient protection.

“For others, it remains to be seen if a fourth booster dose is required over time as it does not appear to be necessary from what we know with the Omicron surge,” Auwaerter said. “If a new variant subsequently emerges, that evades vaccine protection or is more virulent if acquired, we may see reformulation of the vaccine to suit.

Can Waiting Too Long Be Risky?

According to Wetzler and the CDC, getting the first vaccine shot gives you some protection against COVID-19, but immunity can wane over time. The second shot of the two-dose vaccines is essential for reaching immunity against COVID-19.

Studies shared by the CDC have shown a single dose of the Pfizer vaccine ranged from 60% to 80% effective against COVID-19. But both doses were 90% effective against COVID-19 with a higher rate of effectiveness against serious cases of the virus.

Wetzler said if people wait beyond the recommended guidelines to get their second dose, it can impact the body’s ability to develop a good, protective, and full-immune response.

“Now if you get the second shot too soon there really is no risk, but you might need to get another shot a couple of weeks after that,” he said. “If you get it a week later after your first shot, you might not induce a good immune response if you were to wait three or four weeks later.”

He adds even if your second shot is delayed for weeks or even months, you should still get it as soon as possible as the second dose provides added protection.

In the updated guidance, the CDC has not changed the interval of at least five months between completing the initial two-dose vaccine series and receiving a booster shot.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.