A year after the outbreak of the disease that killed 2 million people, people still underestimate the SARS-CoV-2 virus.
This winter, Covid-19 appears to be even more dangerous than epidemiologists and public health officials feared – and not just because of the more contagious variants now moving around the world. As recently as October, Earth reports that it is “too early to say whether Covid is seasonal like the flu.” Evidence has suggested that winter weather may increase the transmission of the virus: In the laboratory, the virus persisted under cold, dry conditions and was inactivated by the ultraviolet rays in sunlight.
There was reason to hope that was not the case. Coronaviruses, which generally show less seasonal variation than the influenza virus, tend to have a poor response to changing temperatures. 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 the idea.
Yet SARS-CoV-2 appears to be different, and the world may face a bigger battle this winter than expected. “People think they’re looking at something like the flu, and it’s much worse,” said Professor Richard Carson, who published a preview in November suggesting that Covid’s response to changing temperatures, known as the temperature response curve, may be even greater. can be pronounced. as influenza, the ultimate seasonal virus. “A lot of things people do in the summer, we think work, are actually warmer temperatures that make the appearance of these things work.”
A lot of things that people do in the summer, we think work, are actually warmer temperatures, which gives the appearance of these things.
Carson and his co-authors at the Massachusetts Institute of Technology and Wake Forest University came to this conclusion by digging up a unique dataset: states’ death certificate records. Statistics on the number of Covid-19 cases and deaths in the US are notorious. Local and state governments do not report standardized data. Laboratories overwhelmed by tests may delay the reporting of positive cases long after the tests have been administered. Deaths reported on a particular day may have occurred weeks in advance. All these inaccurate counts try to measure the role of temperature in transmission speeds.
But Carson’s team, with experience in applying econometric techniques to modeling and predicting environmental impacts, found a solution last year in Massachusetts’ Covid-19 statistics. “The funeral was buried deep in the report by the date on the death certificate,” he said. “After we found it, it took us two months to get the data from most major states.” By extracting dates from death certificates, the team can match the trends in Covid-19 deaths to the maximum daily temperature for a period of three months between April 16 and July 15.
According to the research (pdf) now being conducted by peer review, the data show that the virulence of the virus is rising below 31 ° C (88 ° F). Its ‘sweet spot’, says Carson, is about 4.4 ° C (40 ° F), but that’s just the preferred condition. Temperatures between 5 ° C and 10 ° C (41 ° F to 50 ° F) favor transmission and infection.
The model of the study showed a strong correlation between changing temperatures and the number of Covid-19 cases and deaths from a baseline of 31°C, the average of the US in mid-summer. By the time the weather drops to a cold 5 ° C, the model shows that deaths increase by 160%, just because of the influence of cold weather, even after there were direct commands.
Covid-19 broadcasts showed an even stronger effect. Four times more new Covid-19 positive cases are expected when the temperature drops to 5 ° C, assuming no other interventions such as masks or social distance. Only when the temperature drops a few degrees below freezing, and the point when water droplets freeze rapidly in the air, does Carson and his team project the transfer.
“It’s a scary article,” says Carson. ‘We know the temperature response curve for flu. This one is much steeper. ”
Carson et. al. 2020
For most of the U.S., which sits in the northern hemisphere, a temperature response curve like this is creating a treacherous winter. The delay in the response to increased virus activity, according to the data, will in some cases lead to a rapid escalation due to the feedback loop between cold temperature and the exponential growth curve of the virus. “The patterns of the mid-December outbreak are almost exactly what the temperature response would predict,” Carson said.
Adam Kaplin, a physician and researcher in public health at the John Hopkins University School of Medicine, was not surprised. “It’s really hard to see it any other way,” he said. Following a similar conclusion in his recent research (pdf) to the journal PLOS ONE. “Virus transmission will increase due to the temperature. It’s clear. ”
Virus transmission will increase due to 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, enabling his international team of researchers to isolate the influence of temperature. They found that the temperature for each grade dropped between 30 ° F and 100 ° F, the transfer rate increased by 3.7%
If this ‘strong and robust’ association is correct, the newspaper reads, countries should spend their spring and summer months with the virus to have any hope of containing winter outbreaks, given the effects of falling temperatures. “It’s a race we should have had much earlier,” said Kaplin. “It simply came to our notice then. We blew it up and many people died who did not need to die. ”
What causes it?
Viruses kill millions of people every year, yet we know shockingly little about why their virulence varies from season to season. The spread of the flu’s winter is usually attributed to human behavior patterns – to stay indoors, where germs spread more easily – but the explanation has been questioned. “I do not think you will find a uniform answer to this question,” said Joe Eisenberg, chairman and professor of epidemiology at the University of Michigan’s School of Public Health. “This research has not been prioritized in the past.”
Carson could not explain the relative influence of viral biology and human behavior on the SARS-CoV-2’s response to cold temperatures. His research could only eliminate humidity as a likely factor in transmissibility; temperature and UV light (which in the slot varies with temperature) were much better at explaining Covid-19 transmission patterns.
But Kaplin believes the evidence points to a very strong candidate. “This is the biology of the virus,” he argues. “Yes, people go in more, but it plays a much less important role than biology.” Nothing in the scientific literature supports the idea that this seasonality is driven by human behavior. In the journal Medical hypotheses, a 2016 report found no evidence that winter pressures can drive seasonal viral transmission, pointing out that time spent indoors in the U.S. changes less than 10% between summer and winter. Evidence in the tropics, where the flu circulates throughout the year, also contradicts this hypothesis.
Policy implications
Reducing the transmission rate will mean doubling the mask and attempts at social distance. Now preventive measures just need to increase, to keep the spread rate of the epidemic in check.
This is a bad prospect. “The biggest policy perception is that the temperature drops every week, you have to lower the effective contact percentage to keep the virus in check and prevent exponential growth,” says Carson. “People don’t do that and that’s why you see the outbreaks.”
The biggest policy perception is that the temperature drops every week, you need to lower the effective contact percentage to keep the virus in check and prevent exponential growth.
The new variant adds a game card to the mix. “This new variant is more portable, but it can still have a strong seasonal signal,” says Eisenberg. “We just do not know.”
So far, policymakers have waited too long to respond to Covid-19’s winter push. In the UK, business has started to pile up again this autumn after a brief summer break. Hospitals have warned of cold weather. But national restrictions were only reintroduced on January 9, when the health care system was already in crisis with the more contagious variant. Today, the UK’s per capita mortality rate due to Covid-19 is one of the highest in the world, and more than 40,000 Covid-19 patients are hospitalized, which was double last year’s high.
The US is even worse. The country never got the pandemic under control. Although the transmission slowed down during the summer, the virus started roaring again. The US is now responsible for 20% of the world’s Covid-19 deaths – despite having less than 5% of the population – and is on track to reach 600,000 deaths by 2021. The only immediate solution is to establish herd immunity before next winter through a mass vaccination campaign reaching more than 70% of the population. If the pandemic continues to spiral out of control, many deaths will be inevitable.
But we can prevent this winter from getting even worse, says Eisenberg. The public health measures we have already taken must be stepped up if we are to keep SARS-CoV-2 in check. “It reinforces our recommendations,” he says, “but it does not change our recommendations.”