The Sheba Medical Centre's findings compare with overall efficacy of about 95 per cent in a two-dose regimen 21 days apart for the shot developed with Germany's BioNTech.

The Sheba study, to be published in The Lancet medical journal, comes a day after Canadian researchers suggested the second Pfizer dose be delayed given the high level of protection from the first shot in order to increase the number of people getting vaccinated.

Their research showed efficacy of 92.6 per cent after the first dose, based on an analysis of the documents submitted by the drug maker from its late-stage human trials to the US Food and Drug Administration in December.

The FDA said in December data from those trials showed the vaccine began conferring some protection to recipients before they received the second shot but more data would be needed to assess the potential of a single-dose shot.

Pfizer has said alternative dosing regimens of the vaccine have not been evaluated yet and the decision resided with the health authorities.

Sheba said among 7214 hospital staff who received their first dose in January, there was an 85 per cent reduction in symptomatic COVID-19 within 15 to 28 days. The overall reduction of infections, including asymptomatic cases detected by testing, was 75 per cent.

Sheba epidemiologist Gili Regev-Yochay cautioned that the cohort studied at the hospital were "mostly young and healthy".

Unlike with Pfizer's clinical trial, "we don't have many (staff) here aged over 65", she told reporters. But she also noted the Sheba study took place during a surge in COVID-19 infections in Israel.

Pfizer declined to comment on the data, saying it was doing its own analysis of "the vaccine's real-world effectiveness in several locations worldwide, including Israel".

Australian Associated Press