If You Got Pfizer, This Is How Protected You Are 5 Months Later, Study Says

The latest data comes from U.K. researchers analyzing more than 400,000 people.

The COVID-19 pandemic has provided more than a year's worth of bad news, but the release of safe, highly effective vaccines provided at least one bright spot in the fight against the virus. But because of the very nature of how vaccines work, health experts began to question how long the initial doses would keep people safe from infection and how urgent a potential booster shot might be. The most recent insight into the issue comes from a new large study that looked into how well recipients of the Pfizer vaccine were protected as early as five months after getting their shots, finding there was indeed a change over time.

RELATED: Pfizer Just Said Doing This "Strongly" Boosts Protection From Delta Variant.

Researchers working with the U.K.'s Zoe COVID Study app analyzed the data of more than 400,000 people who received the Pfizer vaccine to check for efficacy over time. Results showed that the shots provided 88 percent effectiveness against the virus one month after the second dose before dropping to 74 percent five or six months after the shots had been administered.

The team behind the study specified that researchers collected all data after May 26, which is when the Delta variant became the dominant strain in the U.K. They also concluded that the reduction in efficacy over time could potentially explain the recent increase of breakthrough infections in fully vaccinated people. However, they also emphasized that the results didn't mean the shots themselves aren't worth getting.

"Waning protection is to be expected and is not a reason to not get vaccinated," Tim Spector, MB, lead investigator on the Zoe COVID Study app, said while presenting the results during a webinar on Aug. 24. "Vaccines still provide high levels of protection for the majority of the population, especially against the Delta variant, so we still need as many people as possible to get fully vaccinated."

RELATED: If You Got This Vaccine, You May Be More Protected Against Delta.

Spector also estimated that the vaccine's efficacy could drop as low as 50 percent by winter and that findings underscore the need for boosters in some of the population, the BBC reports. Still, another expert involved in the research pointed out that the findings align with what could be expected of the shots over time.

"So we knew there was going to be some leveling off, and the way I look at this is the leveling off is actually a little slower than I would have expected," Alexander Hammers, MD, a professor of imaging and neuroscience at King's College London, said during the webinar, who added that people were "still probably at least 50 percent protected" despite a "waning" in the effectiveness over time. "Remember when the vaccines were first developed, it was hoped that they were to have 60 to 70 percent efficacy, and everybody was pleasantly surprised that they came in well over 80 percent, sometimes well over 90," he pointed out.

Other recent research has found that COVID vaccines may be losing their effectiveness over time. In a study released by the Centers for Disease Control and Prevention (CDC) on Aug. 18, residents of 3,862 nursing homes were analyzed from March 1 to May 9 while Alpha was the dominant variant. Later, about 15,254 nursing homes were analyzed from June 21 to Aug. 1, when the Delta variant had taken over. While the study didn't measure protection against severe illness, results found that the efficacy rates of the vaccines against COVID-19 infections overall dropped from 75 to 53 percent. The study's authors concluded that "additional doses of COVID-19 vaccine might be considered for nursing home and long-term care facility residents."

RELATED: For more up-to-date information, sign up for our daily newsletter.

Similarly, the Zoe COVID Study app's authors also emphasized that not all members of the population will require a booster to shore up immunity to COVID-19. "Many people may not need them. Many people may have had a natural booster because they've already had a natural COVID infection, so will effectively have had three vaccines," Spector said. "So I think the whole thing needs to be much more carefully managed than just giving it to everybody, which would be a huge waste and ethically dubious given the resources we have. I think we need a more targeted approach than last time."

RELATED: If You Did This Before Your Pfizer Vaccine, You May Be More Protected.

Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
Filed Under