Coronavirus in winter could be worse than scientists thought – Quartz

One year after the emergence of the disease that killed 2 million people, humans continue to underestimate the SARS-CoV-2 virus.

This winter, Covid-19 is proving to be even more dangerous than epidemiologists and public health officials feared – and not just because of the more contagious variants now making their way around the world. No later than October, Nature said it was “too early to tell if Covid is seasonal like the flu”. Evidence suggested that winter conditions could increase virus transmission: in the laboratory, the virus persisted in cold, dry conditions and was inactivated by ultraviolet rays from sunlight.

There were reasons to hope this was not the case. Coronaviruses, which generally exhibit less seasonal variation than the influenza virus, tend to have a poor response to changes in temperature. Outbreaks such as the Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) in 2002 were not considered seasonal at all, although the outbreak ended too quickly for scientists to definitively test this idea.

Still, SARS-CoV-2 appears to be different, and the world could face a bigger fight this winter than expected. “People think they’re looking at something like the flu, and it’s a lot worse,” says Professor Richard Carson, who published a pre-article in November suggesting that Covid’s reaction to temperature changes, known as the name of the temperature response curve, could be even more pronounced. than the flu, the ultimate seasonal virus. “A lot of the things people did in the summer that we thought were working were actually warmer temperatures making these things look like they were working.

A lot of the things people did in the summer that we thought were working were actually warmer temperatures making these things look like they were working.

Carson and his coauthors at the Massachusetts Institute of Technology and Wake Forest University came to this conclusion by unearthing a unique data set: state death certificate registries. The statistics on the number of Covid-19 cases and deaths in the United States are notoriously noisy. Local and state governments do not report standardized data. Laboratories overwhelmed with testing can delay reporting positive cases long after testing is administered. Deaths reported on a given day may have occurred weeks before. All of these inaccurate counts prevent attempts to measure the role of temperature in transmission rates.

But Carson’s team, with experience in applying econometric techniques to modeling and predicting environmental impacts, found a solution in the Massachusetts Covid-19 statistical reports last year. “Another death toll as of the date on the death certificate was buried deep in the report,” he said. “Once we found it, it took us two months to get this data from most of the big states.” By extracting dates from death certificates, the team could match trends in Covid-19 deaths to maximum daily temperatures over a three-month period between April 16 and July 15.

According to research (pdf) currently under peer review, data shows that the virulence of the virus increases below 31 ° C (88 ° F). Her “sweet spot,” Carson says, is around 4.4 ° C (40 ° F), but that’s only her preferred condition. Temperatures between 5 ° C and 10 ° C (41 ° F to 50 ° F) promote transmission and infection.

The study model found a strong correlation between temperature changes and the number of Covid-19 cases and deaths based on 31°C, the US mid-summer average. As the weather drops to 5 ° C, the model shows an increase in the number of deaths of 160% due solely to the influence of cold weather, even after controlling the state’s orders for shelters in place.

Covid-19 transmissions have shown an even stronger effect. Four times as many new positive Covid-19 cases are expected when temperatures drop to 5 ° C, assuming no other intervention such as masks or social distancing. It’s only when temperatures drop a few degrees below freezing, when water droplets quickly freeze in the air, that Carson and his team plan to slow transmission.

“This is a really scary article,” Carson says. “We know the temperature response curve for influenza. This one is much steeper.

Carson et. al. 2020

For most of the United States, located in the northern hemisphere, a temperature response curve like this makes for a perilous winter. Any delay in responding to high viral activity, the data shows, will cause cases to escalate rapidly due to the feedback loop between cold temperature and the virus’s exponential growth curve. “The epidemic trends in mid-December are almost exactly what the temperature response would predict,” Carson says.

Adam Kaplin, a physician and public health researcher at John Hopkins University School of Medicine, was not surprised. “It’s really hard to see it any other way,” he said, after reaching a similar conclusion in his recently submitted research (pdf) to the journal PLOS ONE. “The transmission of the virus will increase because of the temperature. It’s clear.”

The transmission of the virus will increase because of the temperature. It’s clear.

Kaplin analyzed SARS-CoV-2 transmission rates and daily temperature records in 50 countries between January and April 2020, a period before most mask orders went into effect, allowing its international team to researchers isolate the influence of temperature. They found that for every degree the temperatures dropped between 30 ° F and 100 ° F, the transmission rate increased by 3.7%

If this “strong and robust” association is correct, the newspaper says, countries must spend their spring and summer months containing the virus if they are to hope to contain winter outbreaks given the effects of lower temperatures. “It’s a race we should have run a lot earlier,” says Kaplin. “We should have been way ahead. We messed this up and many people died without needing to die.

What is causing this?

Viruses kill millions of people each year, but we know very little why their virulence fluctuates from season to season. The winter’s spread of influenza is generally attributed to human behavior – staying indoors, where germs spread more easily – but that explanation has been questioned. “I don’t think you’ll find a uniform answer to this question,” says Joe Eisenberg, president and professor of epidemiology at the School of Public Health at the University of Michigan. “This research was not a priority in the past.”

Carson was unable to determine the relative influence of viral biology and human behavior on the response of SARS-CoV-2 to cold temperatures. His research could only eliminate moisture as a probable factor of transmissibility; temperature and UV light (which fluctuates with temperature) were much better at explaining the patterns of Covid-19 transmission.

But Kaplin thinks the evidence points to a very strong candidate. “It’s the biology of the virus,” he argues. “Yes, people go more indoors, but that plays a much smaller role than biology. Nothing in the scientific literature, he notes, supports the idea that this seasonality is driven by human behavior. In the newspaper Medical hypotheses, a 2016 article found no evidence that winter overcrowding leads to seasonal viral transmission, noting that time spent indoors in the United States changes by less than 10% between summer and winter. Evidence in the tropics, where the flu circulates year-round, also contradicts this hypothesis.

Political implications

Reducing the rate of transmission will involve redoubling efforts at masking and social distancing. Now, preventive measures must be stepped up simply to contain the rate of the epidemic’s spread.

It is a bleak prospect. “The big political notion is that every week the temperature drops, you have to reduce the effective contact rate to control the virus and prevent exponential growth,” Carson says. “People don’t do that, and that’s why you see these epidemics.”

The big political notion is that every week the temperature drops, you have to reduce the effective contact rate to control the virus and prevent exponential growth.

The new variant adds a wild card to the mix. “This new variant is more transmissible, but it can still have a strong seasonal signal,” explains Eisenberg. “We just don’t know.

So far, policymakers have waited too long to respond to the Covid-19 winter surge. In the UK, cases started to pile up again this fall after a brief summer respite. Hospitals have warned of a crush with the onset of colder weather. But national restrictions weren’t reimposed until January 9, when the healthcare system was already in crisis and battling the most contagious variant. Today, the UK’s per capita death rate from Covid-19 is among the highest in the world and more than 40,000 Covid-19 patients are hospitalized, roughly double the peak of last year.

The United States is in an even worse situation. The country has never brought the pandemic under control. Although transmission slowed over the summer, the virus has made a comeback. The United States is now responsible for 20% of deaths from Covid-19 worldwide – despite less than 5% of its population – and is on track to reach 600,000 deaths in 2021. The only immediate solution is to establish collective immunity before next winter thanks to a mass vaccination campaign which reaches more than 70% of the population. If the pandemic continues to get out of control, many more deaths will be inevitable.

But we can prevent this winter from getting any worse, says Eisenberg. The public health measures we have already taken must be stepped up if we are to bring SARS-CoV-2 under control. “It intensifies our recommendations,” he says, “but doesn’t change our recommendations.”