Pfizer’s vaccine is 75 percent effective two to four weeks after a single shot, according to a “groundbreaking” new Israeli study that may guide policy internationally on one of the most burning vaccine questions.
This figure reflects symptomatic and asymptomatic illness. When the Sheba Medical Center team homed in on stats just for people who felt unwell, they found that a single dose has 85% effectiveness.
This constitutes a “very, very significant reduction,” said Prof. Gili Regev-Yochay, Director of Sheba Medical Center’s Infectious Disease Epidemiology Unit.
In some countries racing to vaccinate large populations, doctors are arguing over whether they should delay second shots so they can give more people partial protection with one shot. The UK has controversially adopted this approach, despite growing concern in the medical profession.
On Thursday, Sheba researchers released research which it says supports the UK’s approach. Unlike most of the Israeli data on vaccine effectiveness, which hasn’t yet been subject to peer review, this study has been peer-reviewed and published in the prestigious journal The Lancet.
“This ground-breaking research supports the British government’s decision to begin inoculating its citizens with a single dose of the vaccine,” claimed Prof. Arnon Afek, the hospital’s director-general.
The UK has mainly been using the vaccine created by Oxford University and pharmaceutical giant AstraZeneca, although it has also administered the Pfizer inoculation to some.
Regev-Yochay said that according to her research the first vaccine shot is exceeding expectations set by clinical trials. “In real life we’re seeing excellent results,” she said.
“What we see is really very high effectiveness just two to four weeks after the first shot,” she said.
Regev-Yochay emphasized that she isn’t calling for second shots to be cancelled, but rather suggesting that her research suggests that the policy of delaying second shots isn’t “expensive” in heath terms.
The hospital monitored 7,214 staff from two weeks after their first shot until four weeks, when their second shot kicked in. They compared the results with control data, and concluded that the first shot alone delivers an 85% reduction in symptomatic illness, and a 75% reduction in infection.
Regev-Yochay said that the research is highly reliable, as unlike in general society, where it is hard to predict under what circumstances people will and won’t go for coronavirus testing, her medical staff follow clear protocols.
Staff with symptoms or who are exposed to a coronavirus carrier are strict about submitting themselves for testing, while outside the medical profession “there are many more biases on when people would go to test or not.”
Regev-Yochay noted two limitations to her research. One is that hospital workers tend to be younger and healthier than the general population, and first dose effectiveness may be particularly high for this reason. The second is that it presents only a snapshot in time, from two to four weeks after the first shot, and doesn’t prove how long the impact of the first shot alone will last.
She suggested that Sheba is preparing to release separate research on the extent to which the vaccine stops transmission of the virus, saying there may be “good news on that soon.”