SINGAPORE/JAKARTA -- When Indonesia made it through February without a single coronavirus case, some experts chalked it up to the country's tropical climate. Their reasoning looks a lot less convincing now.
Since reporting its first infections on March 2, Indonesia has logged over 9,000 confirmed cases, the second-highest in Southeast Asia after Singapore -- another place where temperatures regularly exceed 30 C. Indonesia's death rate of around 8% is one of the highest globally.
Yet, as the pandemic drags on around the globe, taking lives and damaging economies, some are clinging to hope that warmer weather might bring at least a degree of relief.
Scientists who spoke with the Nikkei Asian Review, however, stressed that other factors are far more important in determining how much the virus spreads. Put another way, countries should not count on hot climates or the onset of summer to save them.
Here are five things to know about heat and the new coronavirus.
Doesn't heat kill the virus?
It is true that the new coronavirus, like many other viruses, persists in the environment "far longer at the lower temperatures of winter and in a refrigerator, than at warmer temperatures of the tropics," said Eric Yap, associate professor of human and microbial genetics at Nanyang Technological University's Lee Kong Chian School of Medicine in Singapore. "This is the same reason why vaccines and many medicines are best stored in refrigerators during transport."
Theoretically, heat might help to curb transmission if most people were catching the virus by touching a contaminated object, like a handrail, and then rubbing their eyes or biting their nails. The problem, another expert noted, is that this is not how most patients get sick.
"There is a small chance that contact transmission ... could be reduced in very hot climates as the virus may not survive for so long under such circumstances," said Annelies Wilder-Smith, professor of emerging infectious diseases at the London School of Hygiene and Tropical Medicine. "However, the majority of transmission occurs from person to person."
Likewise, a study published by Harvard University researchers in mid-April suggested that warm weather likely does nothing to curb the spread.
Would the outbreaks be worse if countries like Indonesia were colder?
Not necessarily. Researchers from Indonesia's Meteorology, Climatology and Geophysics Agency (BMKG) and Gadjah Mada University reviewed several studies done earlier this year in China, the U.S. and Europe. Summarizing the findings for President Joko Widodo in late March, they said the studies suggested colder, dry climates were a "supporting factor" in the initial outbreak across the Northern Hemisphere.
But they were "not a determining factor."
"People's mobility and social interactions are suspected to have a stronger influence on the COVID-19 outbreak in Indonesia, rather than the climate factor," the researchers said.
Yap rattled off a list of other elements that determine the severity of an outbreak: "Cultural habits like how acceptable is the use of face masks, how much informal interpersonal contact occurs, whether aged live with young, and types of recreational activities. Socio-economic factors such as household density and exposure during work. Finally, medical factors like how many diagnostic tests are available, who is being screened and whether infected people visit doctors."
He said these interacting factors, known to epidemiologists as "confounders," are "very hard to tease apart."
"So it would be hard to conclude that being in the tropics alone makes things better or worse."
Could the virus mutate to better withstand hot weather, becoming even more dangerous?
There have been numerous reports that the coronavirus is mutating, or undergoing slight genetic changes. Researchers at China's Zhejiang University in mid-April posted a study, not yet peer reviewed, that identified 33 mutations, some of which appeared to make the virus far more potent.
"Our study provides direct evidence that mutations currently occurring in the SARS-CoV-2 genome have the functional potential to impact the viral pathogenicity," the researchers wrote in their paper, using the formal name of the virus that causes COVID-19.
Yap argued that such potential changes in "infectivity" -- not heat resistance -- are the real issue.
"I don't think there is any evidence of the virus evolving heat tolerance," he said, adding, "A COVID-19 virus spends most of its life cycle within the warm human host, so the time it spends out of the body is only transient."
More likely to evolve, he continued, is the ability of the virus to move through a population. "Mutations can increase this ease of transmission, for instance if the virus infects the nose, or if the infection induces sneezing or coughing, hence raising the likelihood of droplet spread."
Can we expect the new coronavirus to recede like SARS?
"SARS-CoV-2 is a novel virus and we should not speculate about seasonality by extrapolating from other respiratory viruses," Wilder-Smith cautioned.
She did say the new virus is "very similar" to SARS and MERS, or Middle East respiratory syndrome, which both "transmitted effectively in hot climates."
"We contained SARS because we pulled all the interventions with an incredible political will at the time," she said. "SARS did not disappear because of the summer months. SARS had its highest peak in April, and not in the winter months."
At this point, given the global distribution of the new virus, Wilder-Smith said that "hopes for containment are now very low. We all fear it will linger on, regardless of seasonality, but instead dependent on population densities and the extent of social mixing."
Yap sounded slightly more optimistic -- not that he thinks the virus is going away anytime soon.
"The reassuring thing is that, from the virus' perspective, it would not be at all a successful parasite if it completely eliminated its host, as it would also lead to its very own extinction. We can therefore be reassured that the longer COVID-19 persists in the human population, the less virulent it will evolve to be."
What should countries with warm climates -- and those approaching summer -- expect now?
The jury is still out in Southeast Asia. Vietnam all but declared victory over the virus and eased restrictions. Thailand's lockdown has been holding new cases in the single digits of late. But Indonesia is struggling, reporting hundreds of cases a day as its total surges toward 10,000.
Back in March, researchers at the University of Indonesia's school of public health conducted a study that suggested only 2% of cases were being detected. More recently, the team's math modeling suggested cases could reach 1 million on the island of Java alone in June, based on people's movements and other conditions.
Wilder-Smith was blunt: "Researchers who speculate about warmer temperatures as being 'protective' provide misleading misinformation that will hamper the response."
She continued, "This is an extremely contagious virus that easily spreads from person to person via respiratory droplets. Countries such as Singapore, India, Indonesia -- and basically all countries in the tropics and subtropics -- should prepare for a COVID outbreak and not be falsely reassured that they are protected because of their warmer climates."
Yap, when asked what else scientists are learning as the crisis progresses, emphasized that there are still big gaps in knowledge.
"We're learning that ... there's much more to learn."
Additional reporting by James Hand-Cukierman in Tokyo.