The first dose of the Pfizer COVID-19 vaccination is 85 percent effective against infection between two and four weeks after the first jab, according to a study published in the Lancet medical journal. The overall reduction of infections, including asymptomatic cases detected by testing, was 75 percent.
The results of the pre-published, not yet peer-reviewed study were based on more than 9,000 health-care workers from Israel’s Sheba Medical Center, the country’s largest hospital, more than 7,000 of whom were vaccinated by the end of January.
Researchers looked at the rate of infections during the three weeks or so before the workers got a second dose of vaccine, finding a 47 percent reduction in symptomatic coronavirus infections among the hospital staff during the first two weeks after the first shot and an 85 percent reduction over the following two weeks. That’s compared to an efficacy of around 95 percent for the manufacturer-recommended regime of two doses spaced 21 days apart.
While the results are encouraging, the study had its limitations: It focused only on one hospital, and, as Sheba epidemiologist Gili Regev-Yochay cautioned, the cohort studied was “mostly young and healthy” since they “don’t have many (staff) here aged over 65.”
Researchers write that the findings bolster the case to space out the dosing regimen amid vaccine supply issues by “delaying the second dose in countries facing vaccine shortages and scarce resources, so as to allow higher population coverage with a single dose,” a strategy the United Kingdom has controversially adopted.
The study, though, does not determine how long the protection from just one dose will last. Researchers who worked on the study add that more comprehensive follow-up studies assessing the long-term effectiveness of a single dose will be needed to inform any policies delaying the second dose.
Pfizer declined to comment on the data, saying in a statement it was doing its own analysis of “the vaccine’s real-world effectiveness in several locations worldwide, including Israel,” according to Reuters.
