But a new study, by Dr. Juni, an epidemiologist, and his colleagues in Canada and Switzerland, offers very little encouragement for warm-weather worshipers. In countries around the world, his research found, variations in heat and humidity had little to no effect on the spread of the pandemic. Differences in how the disease spread were instead strongly associated with public health measures like social distancing and school closures.

Several other studies have found or projected modest effects of warmer climates or the increase of sunlight in diminishing the spread of the coronavirus, but all have emphasized the need for public health interventions.

One reason is that most of the world’s population has no immunity to the virus. “This means the virus doesn’t need favorable conditions” to spread, Dr. Juni said.