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February 22, 2021

Pfizer's COVID-19 vaccine cuts risk of asymptomatic infection, U.K. data shows

Elderly people are much less likely to be hospitalized or die of the coronavirus if they are vaccinated

The Pfizer-BioNTech COVID-19 vaccine reduces the risk of infection by 72% after the first dose and by 85% after the second dose, according to data released Monday by the United Kingdom. 

The research, conducted by Public Health England, involved health care workers under 65 who were tested for COVID-19 every two weeks using PCR tests and twice a week using rapid diagnostic tests. 

That testing regimen offered a glimpse at the Pfizer vaccine's ability to prevent asymptomatic infections. Clinical trials had examined its ability to prevent symptomatic infections. 

"Overall we are seeing a really strong effect to reducing any infection: asymptomatic and symptomatic," Susan-Hopkins, strategic response director at Public Health England, said in a press briefing.

Broader testing among 12,000 people in the overall population found a single dose is 57% effective against symptomatic COVID-19 in people over age 80. Just one week after the second dose, that figure jumps to 88%. 

The vaccine was found to be highly protective against the B.1.1.7 variant identified in the United Kingdom last fall.

The data also showed that vaccinated people who contract the coronavirus are less likely to be hospitalized or to die from COVID-19. 

People 80 and older — among the most vulnerable — were 41% less likely to be hospitalized with COVID-19 if they were at least 14 days removed from their first COVID-19 shot. They were 57% less likely to die of the illness. 

"This is strong evidence that the Pfizer-BioNTech vaccine is stopping people from getting infected, while also protecting cases against hospitalization and death," said Dr. Mary Ramsay, head of immunization at Public Health England. 

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