The first dose of Pfizer Inc’s COVID-19 vaccine is 85% effective, a study of healthcare workers at an Israeli hospital has found, potentially fuelling a debate over the recommended two-dose schedule as governments try to stretch out supplies, Reuters reports.

The Sheba Medical Center’s findings compare with overall efficacy of around 95% 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 that 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% after the first dose, based on an analysis of the documents submitted by the drugmaker from its late-stage human trials to the U.S. Food and Drug Administration in December.

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.” It hopes to use Israeli data to look at the potential of the vaccine to protect against COVID-19 arising from emerging variants, the drugmaker said.