At a briefing in late April, President Trump and Vice President Pence promoted a laboratory study with promising results. It suggested that heat and humidity could be a factor in reducing transmission rates of the novel coronavirus.

The results of that research, which was conducted by the Department of Homeland Security and peer reviewed after the briefing, showed that the virus’s half-life on nonporous surfaces decreased substantially when exposed to sunlight and high humidity, The Post’s Andrew Freedman and Jason Samenow reported at the time.

Though the study did not conclude that the summer would kill the virus, William N. Bryan, acting undersecretary for science and technology at the Homeland Security Department, called increased temperatures “another tool in [the] toolbox” to combat covid-19.

However, around that time, outside experts cautioned that any benefit from summer conditions would probably be lost if people mistakenly think the virus can’t spread in warm weather and abandon efforts that limit infections, such as social distancing.

Newly reported cases of the novel coronavirus in the United States reached their highest levels in July and continue to ascend, a troubling trend that shows it will take a lot more than heat to slow the spread, said Aaron Bernstein, interim director for Climate, Health and the Global Environment at the Harvard T.H. Chan School of Public Health.

“We now know that the summer is not going to grant us reprieve,” Bernstein said Friday. “It’s certainly possible that warm weather and humidity can slow the spread of the virus, but it’s clearly not enough to stop widespread transmission.”

He added: “Whether there is any effect of temperature and humidity, it’s not enough.”

States with notoriously hot summers such as Texas and Florida have seen cases rise sharply in the months of June and July, according to Washington Post tracking. Those two states, along with Arizona and California, have emerged as the latest virus hotspots, where medical centers are struggling to keep up with new hospitalizations.

States have grappled with new cases amid their reopening efforts. On June 25, Texas paused its reopening in an attempt to stymie recent spikes. The next day, Florida’s Department of Business and Professional Regulation said it would close bars across the state after some started reopening earlier in the month.

“We’ve known since the beginning that indoor spaces are high-risk. Crowded indoor spaces where people may not move around very much may be particularly risky,” Bernstein said, noting that people tend to congregate inside to avoid the heat. “I’m not alone in saying I’m very concerned — we were hoping to have this situation under much better control. So many other countries are doing much better than we are — now we’re potentially heading into the fall with so many more cases, and we’ll have our usual cold and flu season.”

Abnormally hot conditions predicted across the Lower 48, including in many Southern states where cases are spiking, might keep more people indoors.

As states across the country grip with overflowing hospitals and a dearth of personal protective equipment for doctors, Bernstein predicted the situation won’t improve if people choose not to take common-sense precautions.

“What we know is that while many places have been able to effectively subdue the virus through social distancing and mask-wearing and contact tracing, we have not done those things,” he said. “At this point, we have no choice but to socially distance. To not do so, to not wear masks — to choose supposed freedom through flouting science and knowledge to endanger our fellow citizens — will only land us in deeper trouble.”

Jason Samenow and Andrew Freedman contributed to this report.

Correction: A previous version of this story reported the study that the Trump administration promoted in April was not peer reviewed. It wasn’t peer reviewed at the time of the briefing, but was peer reviewed after the briefing. This story has been updated.