Researchers on Wednesday urged governments to delay administering the second dose of Pfizer Inc's COVID-19 vaccine, which they said had an efficacy of 92.6% after the first dose.

The researchers, Danuta Skowronski and Gaston De Serres, said their findings were derived from Pfizer's documents submitted to the US Food and Drug Administration.

They cautioned that there may be uncertainty about the duration of protection with a single dose, but said that the administration of the second dose a month after the first provided "little added benefit in the short term".

"Given the current vaccine shortage, postponement of the second dose is a matter of national security that, if ignored, will certainly result in thousands of COVID-19-related hospitalizations and deaths this winter in the United States," the authors warned.

In its response, Pfizer said that alternative dosing regimens of its vaccine had not yet been evaluated and that the decision to do that resides with the health authorities.

"We at Pfizer believe that it is critical for health authorities to conduct surveillance on implemented alternative dosing schedules to ensure that vaccines provide the maximum possible protection," it added.