In this week’s edition of the Covid Q&A, we look at what the cold weather might bring for the virus. In hopes of making this very confusing time just a little less so, each week Bloomberg Prognosis is picking one question sent in by readers and putting it to experts in the field. This week’s question comes to us from Rebecca in Albany, New York. She asks:
What will happen to infection rates in the U.S. when cold weather returns next fall?
While many parts of the world are still battling outbreaks of Covid-19, this summer in the U.S. it’s started to feel like the pandemic is over. Many states have completely done away with restrictions, and national case numbers are at their lowest levels since the pandemic began. But new, more contagious variants of the virus are on the rise, and there are regional pockets of vaccine holdouts that threaten to keep Covid in circulation.
All this suggests, unfortunately, is that it’s likely the U.S. isn’t done with the coronavirus just yet. “While it’s not purely a function of cooler temperature, Covid will rise again in the fall (if it doesn’t before),” says Andrew Noymer, a professor of public health at University of California, Irvine. “Covid’s future is as a seasonal disease in the fashion of influenza — and Covid’s future is now. Covid will be back in the fall or winter, or both.”
Without U.S. inoculation rates far higher than their current level, Noymer says, vaccines are unlikely to stop a cold-weather surge. “The vaccines will make the coming wave less severe than the one that crested in January 2021, but vaccination rates are currently not high enough to prevent another wave,” he says.
A resurgence was always likely, he says, but more contagious strains like the delta variant first identified in India may make the wave come sooner. “Every major viral respiratory disease is seasonal with a winter dominance,” he says. “Influenza doesn’t vanish, and neither will Covid.”
Ali Mokdad, a professor of health metrics sciences at the University of Washington, said that projections by the school’s Institute for Health Metrics and Evaluation show a slow rise in cases in early September that will pick up with winter and peak in late January or early February. How bad it gets, he says, will depend on vaccination coverage, the variants in circulation and whether people return to habits like mask-wearing.
Still, several Covid vaccines appear to be far more efficacious than those for the seasonal flu. That means that while we may see a resurgence of the coronavirus, the worst is still most likely behind us.
Track the virus
Almost one in five young adults in the U.S. was neither working nor studying in the first quarter as Black and Hispanic youth remain idle at disproportionate rates. The increase last quarter appears to be driven largely by joblessness, while school attendance rose moderately as campuses started to reopen, according to the study. Young adults are still experiencing double-digit unemployment rates.
Inactive youth is a worrying sign for the future of the economy, as they don’t gain critical job skills to help realize their future earnings potential.
People will be interacting more often indoors in places with poor ventilation, which will increase the risk of transmission, says Mauricio Santillana, a mathematician at Harvard Medical School in Boston, Massachusetts, who models disease spread.
But even if there is a small seasonal effect, the main driver of increased spread will be the vast number of people who are still susceptible to infection, says Rachel Baker, an epidemiologist at Princeton University in New Jersey. That means people in places that are going into summer shouldn’t be complacent either, say researchers.
“By far the biggest factor that will affect the size of an outbreak will be control measures such as social distancing and mask wearing,” says Baker.
Evidence so far
Seasonal trends in viral infection are driven by multiple factors, including people’s behaviour and the properties of the virus — some don’t like hot, humid conditions.
Laboratory experiments reveal that SARS-CoV-2 favours cold, dry conditions, particularly out of direct sunlight. For instance, artificial ultraviolet radiation can inactivate SARS-CoV-2 particles on surfaces1 and in aerosols2, especially in temperatures of around 40 °C. Infectious virus also degrades faster on surfaces in warmer and more humid environments3. In winter, people tend to heat their houses to around 20 °C, and the air is dry and not well ventilated, says Dylan Morris, a mathematical biologist at Princeton. “Indoor conditions in the winter are pretty favourable to viral stability.”
To assess whether infections with a particular virus rise and fall with the seasons, researchers typically study its spread in a specific location, multiple times a year, over many years. But without the benefit of time, they have tried to study the seasonal contribution to SARS-CoV-2 transmission by looking at infection rates in various places worldwide.
A study4 published on 13 October looked at the growth in SARS-CoV-2 infections in the first four months of the pandemic, before most countries introduced controls. It found that infections rose fastest in places with less UV light, and predicted that, without any interventions, cases would dip in summer and peak in winter. In winter, “the risk goes up, but you can still dramatically reduce your risk by good personal behaviour”, says Cory Merow, an ecologist at the University of Connecticut in Storrs, and a co-author of the study. “The weather is a small drop in the pan.”
But Francois Cohen, an environmental economist at the University of Barcelona in Spain, says that testing was also quite limited early in the pandemic, and continues to be unreliable, so it is impossible to determine the effect of weather on the spread of the virus so far.
Baker has tried to tease apart the effect of climate on the seasonal pattern of cases during the course of a pandemic, using data about the humidity sensitivity of another coronavirus. She and her colleagues modelled5 the rise and fall in infection rates over several years for New York City with and without a climate effect, and with different levels of control measures.
They found that a small climate effect can result in substantial outbreaks when the seasons change if control measures are only just managing to contain the virus. “That could be a location where climate might nudge you over,” Baker says. The team posted its results on the preprint server medRxiv on 10 September; the authors suggest that stricter control measures might be needed during winter to reduce the risk of outbreaks.
In the future
If SARS-CoV-2 can survive better in cold conditions, it’s still difficult to disentangle that contribution from the effect of people’s behaviour, says Kathleen O’Reilly, a mathematical epidemiologist at the London School of Hygiene and Tropical Medicine. “Flu has been around for hundreds of years and the specific mechanism as to why you have peaks of flu in the winter is still poorly understood,” says O’Reilly.
And even if researchers had more reliable data for SARS-CoV-2, they would see only small or negligible seasonal effects so early in the pandemic, when much of the population is still susceptible, says Relman.
Over time, however, seasonal effects could play a more important part in driving infection trends, as more people build up immunity to the virus. This could take up to five years through natural infection, or less if people are vaccinated, says Baker.
But whether a seasonal pattern emerges at all, and what it will look like, will depend on many factors that are yet to be understood, including how long immunity lasts, how long recovery takes and how likely it is that people can be reinfected, says Colin Carlson, a biologist who studies emerging diseases at Georgetown University in Washington DC.
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The COVID-19 pandemic has resulted in misinformation and conspiracy theories about the scale of the pandemic and the origin, prevention, diagnosis, and treatment of the disease. False information, including intentional disinformation, has been spread through social media, text messaging,and mass media. Journalists have been arrested for allegedly spreading fake news about the pandemic. False information has also been propagated by celebrities, politicians, and other prominent public figures. The spread of COVID-19 misinformation by governments has also been significant.
Commercial scams have claimed to offer at-home tests, supposed preventives, and “miracle” cures. Several religious groups have claimed their faith will protect them from the virus. Without evidence, some people have claimed the virus is a bioweapon accidentally or deliberately leaked from a laboratory, a population control scheme, the result of a spy operation, or the side effect of 5G upgrades to cellular networks.
The World Health Organization (WHO) declared an “infodemic” of incorrect information about the virus that poses risks to global health.While belief in conspiracy theories is not a new phenomenon, in the context of the COVID-19 pandemic, this can lead to adverse health effects. Cognitive biases, such as jumping to conclusions and confirmation bias, may be linked to the occurrence of conspiracy beliefs.