CNN  — 

Health care systems in many places struggle in winter. Conditions such as asthma, heart attacks and stroke tend to worsen in colder temperatures, and some infectious diseases like influenza spread more easily, which means facilities face a greater patient load.

This year, the coronavirus pandemic could create the perfect winter storm, and scientists say countries need to prepare for a potential uptick in cases that could be more serious than the initial outbreak.

In cold weather we spend more time indoors in poorly ventilated spaces — exactly the conditions that are likely to make the novel coronavirus spread more easily. What’s more, coronavirus cases will likely become more challenging to track and trace given Covid-19 symptoms are similar to those of winter respiratory bugs. Governments may also find it harder to enact lockdown measures on already quarantine-fatigued populations.

The Northern Hemisphere may have had a mild flu season last winter, but there is still the risk of a flu epidemic this year. Plus, the pandemic has disrupted and stretched health care in many countries, leading to a backlog of patients and exhausted frontline workers who are still reeling from the staggering number of cases so far.

The Academy of Medical Sciences in the United Kingdom has modeled what it described as a “reasonable worst-case scenario.” The number of Covid-19-related hospital deaths between September 2020 and June 2021 in the UK could be as high as 119,900, the academy suggested. This projection is more than double the 45,000 deaths the UK has experienced so far. This number does not include potential deaths in care homes, which have accounted for 30% deaths in England.

“We need to do everything we can to stay healthy this winter and priority must be given to those who are most vulnerable,” said Dr. Stephen Holgate, Medical Research Council clinical professor of immunopharmacology and honorary consultant physician at the University of Southampton and chair of the report.

“We’ve got these three months where things are getting better,” he said. “This is a critical window of opportunity to help us prepare for the worst that winter can throw at us.”

Keep those windows open if you can

Being indoors more during the winter means there’s more opportunity for person-to-person transmission of viruses, the report said. Less daylight means people stay indoors for longer periods, and they’re more likely to drive or use public transport.

Poor ventilation, combined with more crowded spaces, increases the density of virus particles circulating in the air, the report said. Lower humidity, cooler temperatures and darker conditions could also mean the virus lingers longer on surfaces, it added.

“In cold, wet or windy weather people are reluctant to open windows as they create cold drafts and hence they often have lower ventilation rates in winter,” the report said.

“This can be a particular challenge in modern airtight buildings which have very low infiltration rates for energy efficiency and for people on low incomes who are trying to keep heating costs down.”

The Academy of Medical Sciences said that its models indicated that Covid-19 cases would rise again in fall and peak in January and February — the busiest time of year for the country’s National Health Service.

The figures from the Academy of Medical Sciences are based on the assumption that it won’t be possible to introduce a lockdown as effective as the one the UK imposed in March 2020. The model doesn’t take into account the use of potential new drugs, or discoveries about existing drugs such as the steroid dexamethasone, which could reduce death rates. Nor does it take into account other possible treatments or potential vaccines.

Get a flu shot

It was particularly difficult, the report said, to project how seasonal influenza would play out this winter. If often varies in severity from year to year.

It could be that social distancing measures taken to mitigate the spread of Covid-19 could reduce the spread of influenza. Hong Kong, which was an early adopter of Covid-19 infection control measures, had a markedly shorter and less severe influenza epidemic last winter, a study found.

It’s possible, however, to have a cold or influenza at the same time as Covid-19 — and this can increase the risk of sneezing and coughing, making it easier for Covid-19 to spread, said the Academy of Medical Sciences report.

What’s more, flu and other respiratory illnesses that share the same symptoms as Covid-19 are likely to make cases and clusters of coronavirus harder to track. The expected number of people in England and Wales alone who will meet current case definitions for Covid-19 (cough or fever or loss of sense of smell) will rise from 100,000 per day in the summer to 360,000 a day in the winter, according to the report.

One thing all experts agree on unequivocally is that as many people as possible should get the influenza vaccine.