How Long Pfizer & Moderna COVID-19 Vaccines Work

  • New research finds that the mRNA vaccines from Moderna and Pfizer can lose effectiveness over time.
  • Both vaccines lose some effectiveness but are very good at protecting against hospitalization.
  • Some people are currently advised to get booster shots, but experts say overall the vaccines are still very effective.

Being vaccinated is possibly the most important way we can get beyond the COVID-19 pandemic. But researchers have been trying to understand when and if immunity after vaccinations will wane over time.

Recent research finds that protection from currently available mRNA vaccines declines a few months after vaccination.

The question researchers sought to answer is: Do available mRNA vaccines lose their effectiveness, and by how much?

New research, financed by Pfizer and published in The Lancet, finds that while the Pfizer mRNA vaccine was 88 percent effective at preventing infection during the first month after a second dose — it was only 47 percent effective at preventing infection 5 months later.

Researchers also found that the Pfizer vaccine was highly effective against the Delta variant, and was still more than 90 percent effective against it for around 4 months, after which it dropped to just 53 percent effectiveness at about 5 months after vaccination.

However, the vaccine’s protectiveness against hospitalizations remained high overall, providing 93 percent protection up to 6 months after being administered.

The study analyzed electronic health records of more than 3 million members of Kaiser Permanente Southern California from when the vaccine was made available in December 2020 to August 2021.

The findings suggest that waning immunity was due to the time that passed after someone received the second dose — and not exposure to the Delta variant.

“Our results provide support for high effectiveness of BNT162b2 against hospital admissions up until around 6 months after being fully vaccinated,” the study authors wrote. “Even in the face of widespread dissemination of the Delta variant.”

A recent study by Brigham and Women’s Hospital (BWH) researchers concluded that the Moderna COVID-19 vaccine was 93 percent effective at preventing illness, and more than 98 percent effective for preventing severe illness even 5 months after a second dose.

The vaccine trial included 30,415 participants, with 15,209 receiving Moderna’s vaccine and 15,206 given a placebo.

According to researchers, the Moderna vaccine showed continued effectiveness at preventing COVID-19 and severe illness even after 5 months, while maintaining an acceptable safety profile and protection against asymptomatic infection.

“The message here is not that if you were vaccinated early, you’re not protected. Those vaccinated more recently may be experiencing a marginal improvement,” co-corresponding author Lindsey Baden, MD, division of infectious diseases at BHW said in a statement. “But both groups are benefiting from protection compared to people who remain unvaccinated.”

“Waning immunity happens to some extent with all vaccines, but that does not mean that the vaccines stop working completely,” David Hirschwerk, MD, an infectious disease specialist with Northwell Health in Manhasset, New York, told Healthline.

“But their effectiveness often reduces as times moves along,” he continued.

He emphasized that COVID-19 vaccines remain “very effective” at preventing severe illness well beyond 6 months.

“But they become steadily less effective at preventing any degree of infection.”

Eric Ascher, a family medicine physician at Lenox Hill Hospital in New York, pointed out that reduced efficacy doesn’t mean you’re suddenly unprotected.

“Because certain immune cells still remember how to protect you from severe disease,” he explained. “Vaccines prevent against severe disease and hospitalization.”

“We see with vaccination, those with breakthrough infections still do very well — much better than those without vaccination and also have a more difficult time spreading disease,” he continued.

Ascher noted that waning immunity is expected with vaccination, and booster doses can remedy that drop in protection.

He confirmed that many vaccines require boosters, an example being the tetanus and pertussis shots.

“After you are vaccinated, there is a burst of protection. Over time, there is the potential for immunity to wane — however, it is important to remember that you are still protected,” he said. “You have many different cells in your body that are still activated long after vaccination that allow you to be protected against severe virus.”

According to Ascher, with this in mind, the benefits from receiving a booster dose outweigh any risks.

“So, we are recommending boosters presently for those high risk populations to allow for that extra burst of protection,” he said.

Ascher explained that each new infection presents an opportunity for the coronavirus to mutate, or slightly change its form.

“The virus is like a game of telephone — with each new case, a new interpretation may spread.”

He noted that when the virus changes significantly, we see a new variant.

“The vaccine does a wonderful job at protecting against the variants in circulation based on the way mRNA works,” he said. “However, scientists expect that if the virus changes faster than folks are vaccinated, we may need an entirely new vaccine.”

Hirschwerk agreed, saying, “This is something that is being watched closely.”

Ascher said the takeaway is that we should all be vaccinated and seek a booster dose as soon as the opportunity arises, as it’s our best protection.

He also pointed out that waning immunity doesn’t mean people who are vaccinated are ‘no longer protected,’ just not protected as robustly.

“Imagine ground coffee beans — over time, you can still make a good pot of coffee, but the flavor isn’t as potent as when the beans are first ground,” he said. “The medical community expects this; this is the way science and vaccinations work.”

New research finds that the mRNA vaccines from Moderna and Pfizer can lose effectiveness over time.

However, both vaccinations provide strong protection against hospitalization.

Experts say that waning protection is normal and seen with many other vaccines.

They also say the benefits far outweigh any risk of receiving a booster shot, and we should get our boosters as soon as we’re eligible.

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