Research shows that sunlight, heat and humidity could weaken the coronavirus on hard surfaces and in the air, a federal official said at the White House coronavirus task force briefing on Thursday.

William Bryan, the acting head of the Science and Technology Directorate at the Department of Homeland Security, presented what he called "emerging results" that showed that the virus within droplets of saliva survives best in indoor and dry conditions.

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"Our most striking observation to date is the powerful effect that solar light appears to have on killing the virus, both surfaces and in the air. We've seen a similar effect with both temperature and humidity as well, where increasing the temperature and humidity or both is generally less favorable to the virus," Bryan said.

DHS did not immediately respond to a request to share the research for review. Some preliminary studies have suggested that hotter temperatures could be unfavorable to the spread of the virus. However, the virus still spread in countries in which it was summer.

The virus dies the quickest in the presence of direct sunlight under the conditions studied, Bryan said.

"While there are many unknown links in the COVID-19 transmission chain, we believe these trends can support practical decision making to lower the risks associated with the virus," Bryan said.

President Donald Trump asked task force member Deborah Birx if it's possible to use light and heat to kill the virus in people. She said it's not something she is aware of, but added that fever is a "good thing" that helps a body respond to infection.

"I hope people enjoy the sun, and if that has an impact, that's great," Trump said.

Trump has been saying the outbreak would ease by summer. He said at Wednesday's briefing that only "embers" of the coronavirus might remain to be put out in the fall and winter. He added that it is possible the virus won't be present at all in the fall, but infectious disease expert Anthony Fauci later in the briefing indicated that he is "convinced" the virus will be around in the fall.

Bryan said it would be "irresponsible" to say that the summer will completely kill the virus. Instead, he said any downtick in the outbreak over the summer could be used as an "opportunity to get ahead."

The president also said that it is possible the White House will extend federal social distancing guidelines beyond April 30, when they are currently set to expire.