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Two doses of Pfizer, Moderna COVID-19 vaccines provide greater protection than just one

A growing percentage of people have missed getting their second shot. Getting just one dose is less effective and has more unknowns than the recommended two doses.
Credit: AP Photo/Mary Altaffer
A pharmacist prepares a syringe with the Pfizer-BioNTech COVID-19 vaccine at a COVID-19 vaccination site at NYC Health + Hospitals Metropolitan, Thursday, Feb. 18, 2021, in New York.

Data from the Centers for Disease Control and Prevention (CDC) shows nearly 8% of Americans who received the first dose of one of the vaccines developed by Pfizer and Moderna have missed getting their second dose. That percentage has risen as the country’s vaccine rollout has expanded to more people.

In response to the information, many people on social media have urged others to get the second vaccine shot, saying it offers greater protection against COVID-19.


Does the second dose of the Pfizer and Moderna vaccines provide greater protection against COVID-19?



This is true.

Yes, getting two doses of the Pfizer and Moderna vaccines provides greater protection against COVID-19.


There have been three COVID-19 vaccines approved by the FDA for emergency use authorization in the U.S. One was developed by Pfizer, another by Moderna and the other by Johnson & Johnson.

The CDC and FDA recommend people get two doses of the vaccines developed by Pfizer and Moderna. The vaccine developed by Johnson & Johnson is a single-shot vaccine.

The recommended time between the two doses is different for each vaccine. For the Pfizer vaccine, the CDC says people should get their second dose three weeks after the first. For the Moderna vaccine, the CDC recommends four weeks between doses. The CDC says the longest people should wait between doses is six weeks. However, if someone receives their second shot earlier or later than the recommended timeline, they do not need to restart the vaccine series, according to the CDC.

Data from the CDC indicates there has been an increase in the percentage of people who have not gotten a second dose of the Moderna or Pfizer vaccines after receiving their first. Of people who had a sufficient amount of time to get their second dose by April 9, nearly 8% had not, according to the CDC. That’s a jump from the 3.4% of people who did not get a second dose from mid-December through mid-February.

The CDC said the increase in missed second doses was expected as vaccine eligibility expanded to more people. The federal agency said groups initially prioritized to get the COVID-19 vaccines were more likely to be vaccinated at work, like health care providers, or where they lived, like long-term care facilities, which could have reduced barriers for getting the second dose. Still, the CDC said further analysis is needed to better understand why more people are not getting the second shot.

Data from the CDC and FDA show getting the second dose of the Pfizer or Moderna vaccines provides greater protection against COVID-19. The FDA reported the vaccine developed by Pfizer was 95% effective in preventing COVID-19 among clinical trial participants. The vaccine developed by Moderna was 94% effective in clinical trials, according to the FDA.

A real-world study by the CDC showed the risk of COVID-19 infection for people who had two doses of the Pfizer or Moderna vaccines was reduced by 90% two or more weeks after receiving the second dose. For people who had just one dose of either vaccine, the risk of infection was reduced by 80% two or more weeks after vaccination.

“The current results provide reassurance that people start to develop protection from the vaccine two weeks after their first dose,” the CDC said. “The greatest protection was seen among those who had received both recommended doses of the vaccine.”

There are other unknowns that come with getting just one dose of the Pfizer or Moderna vaccines instead of the recommended two doses, according to Dr. Kawsar Talaat, infectious disease physician and assistant professor at Johns Hopkins Bloomberg School of Public Health.

“We don't know how long that one-dose protection will last, because those studies haven't been done,” she said. “And we also don't know how well that protection will work against the variants that everybody is concerned about right now."

Pfizer and Moderna said their vaccines have remained effective in preventing COVID-19 through at least six months after the second dose. The full duration of protection is not yet known, according to the CDC.

While the growing percentage of people not getting the second dose of the Pfizer or Moderna vaccines is concerning, Talaat said it’s notable that 92% of people are following through with recommended two-dose regimen.

“It’s incredibly encouraging because we’re not going to get this pandemic under control until we’re all vaccinated,” she said.

More from VERIFY: Yes, Texas has a COVID-19 case decline, but vaccines are the reason why, experts say

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