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Hoping that we make it to warmer weather before the coronavirus possibly arrives in the United States in force?
Don’t bother, scientists say. Unlike with the seasonal flu, the change of seasons may not matter much to the coronavirus.
While it is possible that this virus, like many other respiratory viruses, will not survive as readily in warm temperatures, it will be encountering a “completely susceptible” U.S. population, said Maciej F. Boni, an associate professor of biology at Pennsylvania State University.
Hardly anyone in this country has been exposed to the new virus (other than some travelers to China and their family members), so there’s been no chance to develop immunity. That means the coronavirus — even if it turns out to be hampered somewhat by rising temperatures — has plenty of opportunity to infect people and get passed along, said Boni, a member of Penn State’s Center for Infectious Disease Dynamics.
“We’re not off the hook just because we’re getting to springtime and the warmer weather," he said.
This week, officials at the U.S. Centers for Disease Control and Prevention said that significant spread of the virus in this country is all but inevitable.
However, it is important to remember that the vast majority of infected people have not suffered severe symptoms, and some have had no symptoms at all. Standard hygiene rules apply. Wash hands after being out in public, and avoid rubbing your eyes and scratching your nose.
Boni, who returned recently from a trip to Vietnam and Thailand, said he was impressed by preparedness measures that had been put in place. Dispensers full of hand sanitizer have been installed in many office buildings and public places. Signs urging people to wash their hands are ubiquitous. Some public events have been scaled back or canceled.
“This is probably the advice that we’re going to have to follow if the epidemic takes off in the United States,” he said.
But for how long? Predicting how a virus will emerge and recede is an inexact science, depending on such factors as how infectious it is, whether it persists in a nonhuman host during the off-season, and human population density and behavior. Climate is just one factor.
In Brazil, which reported its first case of coronavirus this week, Health Minister Luiz Henrique Mandetta expressed optimism that the current warm temperatures will prevent the microbe from spreading. The Southern Hemisphere nation is in the midst of summer.
“Brazil is a country of younger people and is in the summer," Mandetta told the news outlet G1. “This is an unlikely period for a respiratory virus around here.”
Perhaps. But the swine flu of 2009 is a cautionary tale, said David N. Fisman, a professor of epidemiology at the University of Toronto. It showed up in New York in April that year, well after the traditional peak of flu season, and by June, it was classified as an epidemic. Hundreds of schools were closed.
That was a novel type of flu, so the immune systems of most people were “naive" — never before exposed. The new coronavirus has a similar opportunity, Fisman predicted.
“The idea that this will just fade in the summer, never to be seen again is, I think, wishful thinking,” he said.
Yet for established viruses that cause respiratory illness, the numbers of sick people do tend to rise in the fall and winter. That is thought to be partly the result of children returning to school, along with an increase in indoor gatherings. Some of these viruses also survive more readily in cooler, drier air.
Speed of transmission is another factor that can cause a virus to ebb and flow. That can happen when a virus makes its way around the world with the changing seasons in different hemispheres. Depending on how fast the virus spreads from person to person, two or three years might elapse between outbreaks in a given country.
This type of two-year cycle has been seen so far with a polio-like viral illness called acute flaccid myelitis. Cases spiked in 2014, 2016, and 2018 and are expected to rise once again this year.
Seasonal patterns also are seen in viruses transmitted by mosquitoes. When the winged pests are out in force, the diseases they carry rise accordingly. Clean your gutters, so there is no standing water for the insects to breed.
Viruses transmitted through exposure to blood or fecal matter, on the other hand, generally are not seasonal, said Penn State’s Boni, who studies influenza and malaria.
Though the new coronavirus may prove to be transmissible during the spring and summer months, public health experts nevertheless would be delighted if it does not show up in the United States until then. Every additional month of delay means more time to prepare and develop vaccines.
“It’s not so much of a question of if this will happen in this country anymore but a question of when this will happen,” said Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases, during a news conference Tuesday.
But once again, much remains unknown. The genetic code for the new coronavirus has not mutated much since it emerged in late December. So if a vaccine is developed this year, does that mean it will protect people against the coronavirus next year?
Some vaccines, such as the one for measles, confer long-lasting protection, as the genome of that virus remains relatively stable. With the flu, however, new formulations of the vaccine are required every year.
“The measles virus just cannot seem to mutate away from the measles vaccine,” Boni said. “The flu can.”