UK study finds one dose of Pfizer/BioNTech vaccine reduces risk of infection by 72%

Syringes and vials of the Pfizer/BioNTech Covid-19 vaccine ready to be administered to frontline health care workers on December 17, 2020.

London (CNN)New data shows that the first dose of the Pfizer/BioNTech Covid-19 vaccine "provides high levels of protection against infection and symptomatic disease," Public Health England (PHE) said in a press release on Monday.

PHE's Siren Study, which was carried out on healthcare workers aged under the age of 65, found that one dose of the vaccine reduced the risk of infection by 72% after three weeks, while two vaccine doses reduced the risk of infection by 85%. This high level of protection extended to the B.1.1.7 coronavirus variant first identified in the UK in December.
Health workers were tested for Covid-19 infection every two weeks using PCR tests and twice a week with lateral flow tests, Dr. Susan Hopkins, strategic response director at PHE, explained, meaning "there was a lot of asymptomatic testing," she said.
    "Overall we are seeing a really strong effect to reducing any infection: asymptomatic and symptomatic," Hopkins said during a press conference held by the UK's Science Media Centre on Monday.
    PHE also analyzed routine testing data based on symptomatic disease in over 12,000 people, which showed that one dose of the Pfizer/BioNTech vaccine was 57% effective against symptomatic COVID-19 disease in those aged over 80 four weeks after the first dose. This increased to 88% one week after the second dose.