(Reuters) – The second dose of Pfizer Inc’s COVID-19 vaccine could be delayed to cover all priority groups, as the first is highly protective, two Canada-based researchers said in a letter published in the New England Journal of Medicine.
The vaccine had a 92.6% efficacy after the first dose, Danuta Skowronski and Gaston De Serres said, based on an analysis of the documents submitted by the drug manufacturer to the U.S. Food and Drug Administration (FDA).
These findings were similar to the efficacy at the first dose of 92.1% reported for Moderna Inc’s mRNA-1273 vaccine, according to the letter here on Wednesday.
In its response, Pfizer said alternative vaccine dosing regimens had not yet been evaluated and the decision rested with the health authorities.
Some countries, struggling with low stocks, 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 that the urgency of the pandemic requires flexibility, while others oppose abandoning data-driven approaches for the sake of efficiency.
Skowronski and De Serres warned that there may be uncertainty about the duration of protection with a single dose, but said that the administration of the second dose one month after the first was “of little benefit in the short term.”
Skowronski works at the British Columbia Center for Disease Control, while De Serres is at the Institut National de Santé Publique du Québec.
In Britain, authorities have said data supported the decision to switch to a 12-week dosing schedule for Pfizer’s COVID vaccine. Both Pfizer and partner BioNTech have warned they had no evidence to prove it.
The Pfizer vaccine may be taken 21 days apart.
The US FDA and the European Medicines Agency have stuck to the interval tested in the studies.
Reporting by Shubham Kalia and Ann Maria Shibu in Bengaluru; Edited by Vinay Dwivedi and Sriraj Kalluvila