Reuters news agency reported on Thursday that two Canada-based researchers, Danuta Skowronski and Gaston De Serres, on 17 February 2021 have 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, as it was not significantly beneficial in the short term.

Skowronski and De Serres said their findings were derived from Pfizer's documents submitted to the US Food and Drug Administration (FDA).

In their letter published in the New England Journal of Medicine, Skowronski and De Serres said that these findings were also similar to the first-dose efficacy of 92.1% reported for Moderna Inc's mRNA-1273 vaccine.

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".

The researchers warned : "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 hospitalisations and deaths this winter in the US."

In its response, Pfizer said that alternative dosing regimens of its vaccine had not been evaluated yet and the decision to do that resided 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," the company added.

According to Reuters, in the UK, authorities have said that data supported its decision to move to a 12-week dosing schedule for Pfizer's COVID vaccine. Both Pfizer and its partner BioNTech have warned that they had no evidence to prove it.

However, the US FDA and the European Medicines agency (EMA) have stuck by the interval tested in the trials.

Reportedly, the EMA has said there should be a maximum interval of 42 days between the first and the second shot of the vaccine, while FDA mandates a gap of 21 days between the two doses of the Pfizer vaccine.