Pfizer-BioNTech’s COVID-19 vaccine is notably less effective six months after the second dose is administered, a new study finds.
Researchers from King’s College London in the UK analyzed COVID-19 testing data and found the vaccine’s effectiveness falls from 88 percent to 77 percent after five to six months.
They could not determine whether the lower effectiveness caused an increase in hospitalizations or deaths.
The findings could spell trouble in the U.S., where more than 100 million people have received at least one dose of the vaccine – especially as the Indian ‘Delta’ variant continues to spread, causing cases to surge.
Federal officials hope that plans to administer boosters in September – pending approval from the U.S. Food and Drug Administration (FDA) will help shore up protection.
A King’s College study found that the effectiveness of the Pfizer-BioNTech vaccine, the most common in the United States, drops for 88% after one month to 74% after five to six months
The effectiveness begins to slowly wane over time, according to the study, and drops below 75% after five months
The British study, published last week, included 1.2 million participants who had received either the Pfizer or AstraZeneca vaccines.
While not available for emergency use in the U.S., the AstraZeneca vaccine is widely used across Europe.
More than 400,000 participants in the study had been vaccinated with the Pfizer vaccine by July 3.
Britain was hit by a third wave of infections during this period after the more infectious Delta variant sparked outbreaks across the country.
ZOE, a health data science company that contributed to the study, built an app that would ask users to report daily on whether they are unwell, their symptoms and if they have tested positive for the virus.
Using data gathered from the app and Covid testing, researchers determined that a month after vaccination, the vaccine was 88 percent effective.
That figure falls to 74 percent after five to six months.
This means the 92 million Americans who are fully vaccinated with the Pfizer vaccine may have had their protection drop over time.
‘I think the [King’s College London] study and actually, a couple of other studies we recently had, do show the beginnings of a drop off of protection against asymptomatic or mildly symptomatic disease,’ said Professor Adam Finn, head of the Bristol Vaccine Centre in England, and an advisor to the British government on the vaccine rollout.
‘But other studies are showing maintenance of good protection against serious illness and hospitalization.
‘So that’s encouraging actually that people who’ve had two doses are still very much well protected against serious illness, which is our main objective.
‘But we do need to watch out very carefully to see if this waning begins to translate into occurrence of more severe cases because then boosters will be needed.’
The findings match a study released by the Centers for Disease Control and Prevention (CDC) on Wednesday.
Researchers found that the Pfizer and Moderna vaccines were 66 percent effective once the Delta variant, after being 91 percent effective against other strains, hinting at either a waning efficacy of the vaccines or a rare ability for the virus strain to cause breakthrough cases.
In response to the decreasing effectiveness of the vaccines, U.S. health officials announced plans to roll out booster shots last week.
Starting on September 20, all Americans who have received the Pfizer or Moderna vaccines will be eligible for a booster shot eight months after receiving their second shot.
Booster shots are likely on the way for the 14 million recipients of the Johnson & Johnson vaccine, though official plans are yet to have been put in place.
Officials in the UK are still considering how broadly to administer third jabs, but there is pressure from health officials in the country to begin to roll out the shots.
Plans for booster shots have also been put in place in Chile, Germany, Israel and France, among others.
In the meanwhile, the U.S. is suffering from a Delta-fueled surge of Covid cases.
America is averaging 150,000 new cases every day, a 36 percent increase from the 110,000 cases the country was averaging two weeks ago.
The new daily case average is at its highest point since late January, although most cases are concentrated among the unvaccinated.
In the U.S., around 61 percent of the total population has received at least one shot of a COVID-19 vaccine, and 51 percent of people are fully vaccinated.