Wasn’t summer supposed to kill the coronavirus?

When the coronavirus pandemic first reached the U.S. earlier this year, some infectious disease experts were hopeful that COVID-19 would possibly disappear by summer, acting similarly to the seasonal flu which typically dissipates as the weather warms. Even President Trump initially expressed optimism that warmer weather could do away with the virus.

But COVID-19 is not the flu.

As July nears, cases of the novel virus are surging in states across the country, with health officials warning the only way to curb the spread of infection — at least until there is a vaccine — is to adhere to the expert-recommend safety tips, such as social distancing and wearing a face mask.

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“Evidence thus far suggests that the virus that causes COVID-19 can be transmitted in all types of weather,” Dr. William Schaffner, a medical professor at Vanderbilt University and medical director of the National Foundation for Infectious Diseases (NFID), told Fox News via email.

“Regardless of climate, the best way to protect yourself is to wash your hands frequently, stay home as advised, and practice social distancing — stay at least six feet apart — and wear a mask if you do go out in public,” he added.

Dr. John Whyte, the chief medical officer of the health care website WebMD, also expressed doubt that summer weather would do away with the novel virus.

“We originally thought COVID-19 would act similarly to the flu where there would be dissipation during warmer weather, like most respiratory viruses.  Heat and humidity are not a respiratory virus' friend,” he also told Fox News via email. “However, we started to be skeptical of the flu comparison when we saw many cases in regions of the world that were warm/hot in March and April,” such as India, Australia, and Iran, to name a few.

“There are a few reasons why we are likely still seeing a lot of cases. It simply may not be as affected by temperature as other coronaviruses. It may not be as seasonal as the flu. In addition, this virus has a high transmission rate so even in conditions that aren't as favorable, it's still going to spread,” Whyte added, noting that the continued spread is “often dependent on mitigation factors.”

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“As we experience quarantine fatigue, people are not practicing as much physical distancing and mask-wearing. Remember, we were seeing a decrease in cases, especially hospitalizations,” noted Whyte. “There is a concern that as we have reopened, we haven't continued those public health strategies that we know are effective in reducing transmission. In addition, the lack of immunity is continuing to make people susceptible.”

There are at least four pre-existing coronaviruses that are seasonal — but why exactly remains somewhat shrouded in mystery.

For instance, the 2002-2003 outbreak of severe acute respiratory syndrome (SARS), which claimed nearly 800 lives at the time, ended in the summer — but a 2004 report on the seasonality of SARS did not establish a clear reason for why that was.

“Our understanding of the forces driving seasonal disappearance and recurrence of infectious diseases remains fragmentary, thus limiting any predictions about whether, or when, SARS will recur,” the authors wrote at the time. “It is true that most established respiratory pathogens of human beings recur in wintertime, but a new appreciation for the high burden of disease in tropical areas reinforces questions about explanations resting solely on cold air or low humidity.”

More recently, a study published in the Canadian Medical Association Journal in May found that temperature has no clear impact on the spread of the coronavirus.

Researchers with the University of Toronto studied all 144 geopolitical areas worldwide in which 10 or more cases of COVID-19 were documented by March 20, finding almost no links to epidemic growth based on latitude and temperature. However, the researchers did document a strong association with reduced virus spread and restrictions on mass gatherings, school closures, and social distancing — in line with what experts have stressed for months.

“Many experts in the field were hoping the virus would act similar to the flu, where in the winter the virus shell is harder and more protective than in the warmer weather,” Michael J. Urban, the director of occupational therapy at the University of New Haven, told Fox News in an email. “I would be more interested to see how the virus responds in the southern and western parts of the country in late July to August where the heat and humid tends to be at their highest point.”

“COVID-19 is still new," Urban continued. "We have seen a modest slow in areas of the country where social distancing practices and additional measures are in place, yet other areas where the virus is still spreading, such as Florida, relates to the people’s general behavior with regard to being more active as schools end. Many of these regions have also received mixed messages to this point about taking precautions.”

Echoing numerous other health experts, Urban implored Americans to do “their civic duty to the nation by simply wearing a face mask” while outside of their homes. He also mentioned practicing frequent hand washing, staying home when feeling ill and getting tested for COVID-19 “if warranted and available.”

The World Health Organization (WHO) has warned that warmer weather has no impact on COVID-19, noting that one can still contract the virus “no matter how sunny or hot the weather is.”

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Meanwhile, Dr. Anne Schuchat, principal deputy director of the Centers for Disease Control and Prevention, warned that Americans can’t depend on the summer weather to do away with the virus.

“We can affect it, but in terms of the weather or the season helping us, I don’t think we can count on that,” she said during a Monday interview with the Journal of the American Medical Association.

Fox News' Peter Aiken contributed to this story.