Two-dose COVID-19 vaccine from Pfizer and BioNTech offers strong protection against infection in one shot, and likely stops people from spreading the virus, results from large-scale real-world study released Monday.
“One dose reduces the risk of catching an infection by over 70%, dropping to 85% after the second dose,” Public Health England (PHE) said in a press release on Monday. “This suggests that the vaccine can also help stop the transmission of the virus, because you cannot spread the virus if you don’t have an infection.”
The study authors said that “significant protection from infection” began 10 days after the shot and leveled off after 21 days.
The results show that Pfizer’s vaccine works against the UK variant of the coronavirus, called B.1.1.7, which was very common in the UK during the study period, the authors said.
According to the Centers for Disease Control and Prevention (CDC), B.1.1.7 is estimated to be 30 to 50% more contagious and has spread worldwide, including in 44 US states.
More than 32.8 million injection doses of Pfizer have been launched in the United States so far, according to the CDC.
PHE’s ongoing SIREN study followed more than 23,000 UK health workers for two months, testing them weekly for COVID-19, whether or not they had symptoms. They underwent polymerase chain reaction (PCR) tests in the laboratory every fortnight, the gold standard and rapid antigen tests twice a week.
The study then looked at the duration of the COVID-19 infection, confirmed by PCR, and compared those who had been immunized with those who were not. Frequent testing meant researchers could detect people infected with the virus without symptoms, which they used as “a proxy for transmission” – one in three people who have coronavirus have no symptoms but could transmit it without to notice.
The study is a pre-print awaiting review of its methods and conclusions by other experts before publication in the Lancet medical journal.
Another study by health workers in Israel published in the Lancet on February 18 found that Pfizer’s vaccine was effective in protecting against symptomatic infection 15 to 28 days after the first dose, but it did not assess transmission. asymptomatic.
Participants in the SIREN study were of working age, predominantly white women, and three-quarters did not have coexisting medical conditions, so the results may not be generalizable to the general population or the elderly.
PHE said in the press release that early data from routine testing showed that a dose of Pfizer vaccine was 57% effective in protecting against symptomatic COVID-19 disease in people over the age of 80, increasing to over 85% with a second dose.
This effect occurred about three to four weeks after the first dose. The lower efficacy number, compared to the results of the SIREN study, is probably due to the fact that the immune system responds less well to a vaccination as we age. Hospitalization and deaths from COVID-19 have been reduced by more than 75% in those who received a dose of the Pfizer-BioNTech vaccine, PHE added.
A study in Scotland reported similar results on Monday. The study looked at the rate of hospitalization after vaccination and found that the Pfizer injection reduced hospital admissions by up to 85% four weeks after the first dose.
Dr Mary Ramsay, responsible for vaccination at PHE. said there was “strong evidence” that the Pfizer-BioNTech vaccine prevented people from getting infected, while protecting against hospitalization and death.