COVID-19 measures also control influenza — for now | Science

Influenza forecasters are a cautious group. Influenza cases can surge at the end of winter, after months of low infection, and experts hesitate to predict the mild season too early. However, many are ready to declare that COVID-19 controls have dramatically suppressed influenza and other respiratory viruses that normally affect the Northern Hemisphere.

The World Health Organization (WHO) states that influenza activity in the Northern Hemisphere is at “seasonal levels”, as low as normal summer, based on global surveillance data collected by the end of last month. In the United States, the outpatient rate for influenza-like illness is 1.6%, well below the 2.6% baseline used to define seasonal epidemics. The US clinical laboratory has collected 925 positive samples since the end of September 2020, which is 63,975 at this point in the 2019-20 flu season.

“I’m very surprised when the typical flu season comes,” says virologist John McCaulejye, who heads the Worldwide Influenza Center at the Francis Crick Institute in London. “I can’t see anything so far, so it’s hard to know how outbreaks will occur in January.”

For now, it’s safe. Cornelia Adlhoch, an epidemiologist at the European Center for Disease Prevention and Control, said many European countries have stepped up their fall vaccination campaigns for fear of a pandemic and a surge in influenza. In the United States, the US Centers for Disease Control and Prevention has reported a record influenza vaccine distribution. According to the survey, adult vaccination increased from 42% in 2019 to 53% in 2020.

“But I don’t think it’s a vaccine,” explains the mercilessly mild flu season, says McCollie. Instead, he and others point out COVID-19 measures such as wearing masks, social distance, and travel restrictions. Like the southern hemisphere Earlier last year, efforts to completely control SARS-CoV-2 resulted in less infectious seasonal viruses that cause serious illness in infants and the elderly, such as influenza and respiratory syncytial virus (RSV). did.

For Trevor Bedford, a virologist at the University of Washington in Seattle, the unusual flu season represents a challenge. His team will analyze the influenza virus genome collected by WHO’s surveillance network to identify new strains that next year’s influenza vaccine must protect. “In general, we need to look at thousands of viruses, but it’s still challenging,” he says. Only 127 sequences were collected this season between September 1, 2020 and January 1, 2021, compared to 12,218 in the previous year.

Many are genetic variants of the influenza virus that recently emerged in Cambodia, Bangladesh, and India and caused small seasonal outbreaks, says Bedford. “That’s the stock I think we’ll choose [as a component of] Vaccine if you have to choose it today. WHO will convene a group in February to determine the composition of the next vaccine in the Northern Hemisphere.

Innate immunity to influenza can suffer from this unusual season. Less infection in one season can increase the susceptibility population and increase outbreaks in the next season. “As a modeler of the disease … I knew there might be a slight twist,” said Rachel Baker, an epidemiologist at Princeton University. In the November 2020 study Minutes of the National Academy of Sciences, Baker and colleagues have simulated future influenza and RSV outbreaks in more than 300 US counties and Mexican states, assuming a 20% reduction in infections with these viruses this year. In some places, their model predicted an outbreak in the winter of 2021-22. This was twice the size of a normal year.

Increased susceptibility can occur outside the peak season of the virus, Baker said. She suspects it’s happening in Australia. After an unusually low incidence of RSV in winter in the Southern Hemisphere, the country began to lift the blockade. Some Australian states recorded a surge in October 2020 as summer approached and continue to report above-average levels.

However, influenza outbreaks are difficult to predict and may not recover as well, Baker said. In her team’s model, controlling influenza infection in one season did not consistently increase the incidence in the next season. And if concerns about the surge next year cause more flu shots, “a larger outbreak may be thwarted,” she says.

Bedford says less-welcome developments may mitigate the flu surge next year: the resurrection of COVID-19 and the resurgence of loosened controls. “If not enough people are vaccinated during the summer, mainly [because of] “Vaccine hesitation,” he says. “The COVID wave will be a little smaller.”

But even if the COVID-19 threat subsides in the coming winter, mitigation measures may be prolonged, says Benjamin Singer, a lung and life-saving physician at Northwestern University. “When you start thinking about the balance of COVID, flu, and all other respiratory viruses, will the United States and the West start thinking more about wearing masks in public in the winter?” He wonders. “This is an interesting sociological kind of question. How does the COVID experience affect our behavior?”