Canadian doctors urge delaying Pfizer vaccine's second dose as first highly effective

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By Reuters Staff

(Reuters) - The second dose of Pfizer Inc's COVID-19 vaccine could be delayed in order to cover all priority groups as the first shot is highly protective, two Canada-based public health physicians said in a letter published in The New England Journal of Medicine.

The vaccine had an efficacy of 92.6% two weeks after the first dose, Dr. Danuta Skowronski and Dr. Gaston De Serres said, based on an analysis of the documents submitted by the drugmaker to the U.S. Food and Drug Administration (FDA).

These findings were similar to the first-dose efficacy of 92.1% reported for Moderna Inc's mRNA-1273 vaccine, according to the letter published on Wednesday.

In response, authors of the Pfizer vaccine clinical trial report published in December write, "we would like to emphasize that alternative dosing regimens of BNT162b2 have not been evaluated. The decision to implement alternative dosing regimens resides with health authorities; however, 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."

Some countries, grappling with low supplies, are looking at dosing patterns or volumes that differ from how the vaccines were tested in clinical trials.

There are differences over the merits of such strategies, with some arguing the urgency of the pandemic requires flexibility, while others oppose abandoning data-driven approaches for the sake of expediency.

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

Dr. Skowronski is epidemiology lead for influenza and emerging respiratory pathogens at the British Columbia Centre for Disease Control, while Dr. De Serres is a medical epidemiologist with the Institut National de Santé Publique du Québec.

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

Pfizer's vaccine is authorized to be taken with shots 21 days apart.

The U.S. FDA and the European Medicines agency have stuck by the interval tested in the trials.

SOURCE: https://bit.ly/3qxoAt3 New England Journal of Medicine, online February 17, 2021.

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