CHICAGO (WGN) — A pair of researchers from Canada are urging governments to hold off on the second dose of the Pfizer vaccine.

CTV News reports Danuta Skowronski and Gaston De Serres said data shows one shot is more than 92% effective, so a second dose doesn’t add much benefit.

They reported their findings in a letter published in the New England Journal of Medicine Wednesday. Their findings are based on an analysis of documents Pfizer submitted to the U.S. Food and Drug Administration.

The Moderna vaccine’s first-dose efficacy is similar, shown to be 92.1%, according to the letter.

The researchers admit there’s uncertainty about how long immunity will last after a single dose, but they say giving a second shot a few weeks later doesn’t add much protection in the short term.

Pfizer responded by saying it hasn’t evaluated alternative dosing schedules and would leave that decision to health officials, CTV News reported.

Using one dose per person would alleviate vaccine shortages. Health officials and providers say their biggest challenge is the limited supplies and the variability in doses distributed from week to week.

Even with the increase in shipments announced recently by President Joe Biden’s administration, local officials and providers say demand outweighs the number of doses on hand.

Even so, the U.S. is vaccinating an average of 1.7 million Americans per day, up from under 1 million a month ago. And according to data from the Centers for Disease Control and Prevention, much of the increase comes from people receiving their second dose.

The pace of first-dose vaccinations has been largely steady over the past several weeks, hovering around an average of 900,000 shots per day.