The two-dose vaccine COVID-19 from Pfizer and BioNTech provides strong protection against infection with just one injection and is likely to prevent people from spreading the virus, according to the results of a real large-scale study published on Monday.
“One dose reduces the risk of getting infection by more than 70%, increasing to 85% after the second dose,” said Public Health England (PHE) in a press release on Monday. “This suggests that the vaccine may also help stop transmission of the virus, as you cannot spread the virus if you do not have the infection.”
The study authors said that “significant protection against infection” started 10 days after the injection and stabilized after 21 days.
The results show that the Pfizer vaccine works against the UK coronavirus variant, called B.1.1.7, which was highly prevalent in the UK during the study period, the authors said.
B.1.1.7 is estimated to be 30-50% more contagious and has spread worldwide, including 44 states in the USA, according to the Centers for Disease Control and Prevention (CDC).
More than 32.8 million doses of Pfizer injection have been launched in the United States so far, according to the CDC.
The ongoing PHE SIREN study followed more than 23,000 UK healthcare professionals for two months, testing them each week for COVID-19, regardless of symptoms. They had biweekly polymerase chain reaction (PCR) laboratory tests, the gold standard, and rapid antigen tests twice a week.
The study then looked at the time until COVID-19 infection, confirmed by PCR, and compared those who were immunized with those who were not. The frequent test meant that the researchers could detect people infected with the virus without symptoms, which they used as “a replacement for transmission” – one in three people with coronavirus has no symptoms, but could transmit it without realizing it.
The study is a preprint that awaits scrutiny of its methods and conclusions by other experts before publication in the medical journal Lancet.
Another study with healthcare professionals in Israel, published in the Lancet on February 18, found that the Pfizer vaccine was effective in protecting against symptomatic infection 15-28 days after the first dose, but did not assess asymptomatic transmission.
Participants in the SIREN study were of working age, mainly white women, and three-quarters did not have coexisting medical conditions, so the findings may not be generalizable to the general population or older people.
PHE said in the press release that early data from routine tests showed that a dose of Pfizer injection was 57% effective in protecting against symptomatic COVID-19 disease in people over 80, increasing to more than 85% with a second dose.
This effect occurred about three to four weeks after the first dose. The lower number of efficacy, 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 death from COVID-19 were reduced by more than 75% in those who received a dose of the Pfizer-BioNTech vaccine, added the PHE.
A study in Scotland reported similar results on Monday. The study looked at the rate of hospitalization after immunization and found that the injection of Pfizer reduced hospital admissions by up to 85% four weeks after the first dose.
Dr. Mary Ramsay, chief of immunization at PHE. said there was “strong evidence” that the Pfizer-BioNTech vaccine was preventing people from becoming infected, while protecting against hospitalization and death.