How will COVID-19 affect the upcoming flu season? Scientists strive for clues | Science

Science‘s report on COVID-19 is supported by the Pulitzer Center and the Heising-Simons Foundation.

In March, as the southern hemisphere braced for winter flu season while fighting COVID-19, epidemiologist Cheryl Cohen and colleagues at the National Institute of Communicable Diseases of South Africa (NICD) drew up a plan to learn from the double whammy. They hope to study interactions between seasonal respiratory viruses and SARS-CoV-2, which causes COVID-19. Does infection with one change the risk of one person catching the other? How do people earn when they have both?

But the flu season – and the answers – never came. NICD’s Center for Respiratory Disease and Meningitis, headed by Cohen, has reported only one single case since the end of March. In previous years, the country’s surveillance platforms have documented an average of about 700 cases during that period, Cohen says. “We’ve had flu surveillance since 1984, and it’s without a doubt.”

Some cases were likely to be overlooked as clinics temporarily closed and people with mild symptoms avoided medical offices and clinics, Cohen says. “But I do not think it is possible that we will miss the flu season completely with all of us [surveillance] programs. “Apparently, travel restrictions, school closures, social distance, and mask wear have all perpetuated flu in South Africa. Similar stories have emerged from Australia, New Zealand, and parts of South America.

The Northern Hemisphere hopes to be so happy. A few cases in the south could mean a bit of infection spreading north, says Pasi Penttinen, head of the Influenza and Respiratory Disease Program at the European Center for Disease Prevention and Control (ECDC). But if lockdowns and social distance measures are not in place in October, November and December, flu will spread much more frequently than it has in the south, warns virologist John McCauley, director of the Worldwide Influenza Center at the Francis Crick Institute.

The prospect of a flu season during the coronavirus pandemic is cool for health experts. Hospitals and clinics already fear a pile of new respiratory infections, including influenza and respiratory syncytial virus (RSV), another seasonal change that can cause a serious illness in young children and parents. In the United States, where some areas have long been waiting for COVID-19 test results, the delays could grow as flu symptoms stimulate demand. “The need to decide SARS-CoV-2 will be intense,” said Marc Lipsitch of the Harvard TH Chan School of Public Health.

Because the southern hemisphere is largely spared, researchers do not have much evidence on how COVID-19 can affect the course of a flu outbreak. One major concern is coinfection – people getting COVID-19 and flu at the same time, says Ian Barr, Deputy Director of the World Health Organization Collaborating Center for Reference and Research on Influenza in Melbourne, Australia. “Two or three viruses you infect are usually less than one,” he says.

However, the effects of coinfection with SARS-CoV-2 have not been thoroughly studied. In April, a team at Stanford University found that among 116 people in Northern California who tested positive for the coronavirus in March, 24 also tested positive for at least one other respiratory pathogen, often rhinoviruses and enteroviruses that had a cold. cause symptoms, such as RSV. Only one of the patients was affected, although there probably was not as much flu circulating so late in the U.S. season, says Stanford pathologist Benjamin Pinsky, a co-author. The study found no difference in outcomes between COVID-19 patients with and without other infections. But it was too small to draw broad conclusions.

To complicate matters, having one virus can alter a person’s chances of becoming infected with another. Epidemiologist Sema Nickbakhsh and her team at the University of Glasgow have found both positive and negative relationships between different pairs of respiratory viruses, even after adjusting for confounding factors that would cause two viruses to appear simultaneously or at separate times, as their tendency to grow and disappear with the seasons.
Infections with influenza and other respiratory viruses are relatively rare, Nickbakhsh says, and the interactions her group has documented between influenza and other viruses have suggested protective effects. For example, being infected with one type of influenza virus, influenza A, seems to reduce the chance of having a rhinovirus as well, researchers reported in 2019. (The mechanism behind this effect is not yet clear.)

Nickbakhsh is more concerned about RSV, which her team found to have positive interactions with CoV-OC43, a type of coronavirus of the same genus as SARS-CoV-2. It is possible, she says, that having COVID-19 may increase a person’s sensitivity to RSV, or vice versa. Establishing possible interactions between COVID-19 and other infections requires a large number of patient samples tested for SARS-CoV-2 and other respiratory viruses. Rapid, dual diagnostic tests will be important for both research and treatment decisions, says Benjamin Singer, a pulmonary and critical care physician at Northwestern University. The U.S. Food and Drug Administration has issued emergency use authorizations for influenza COVID-19 combination tests developed by Qiagen, BioFire Diagnostics, and the U.S. Centers for Disease Control and Prevention (CDC).

The impressive winter in the Northern Hemisphere has also brought new attention to flu vaccines, which can sustain hospital admissions as health systems deal with the pandemic. Flu vaccines including GlaxoSmithKline and AstraZeneca have announced production increases for the 2020–21 season. The CDC expects a record setting of 194 million to 198 million doses – a 20-million dose increase from last year. Last month, the UK National Health Service announced that it would expand the age groups eligible for a free flu shot among children and adults.

But what if flu season is bad? Going from sources in an immunization campaign necessarily differs from COVID-19 responses, says Penttinen, whose team provides guidance to European member states on flu vaccination. Still, rates of vaccination have long been “suboptimal” in Europe, he added. (Rates among older adults – the target population for the flu vaccine in many countries – vary from 2% to 72.8%, depending on the country, according to the most recent ECDC data, released in 2018.) “I think the trend is to say, ‘We need to put the wrong side on the side of caution – efforts are being made to at least maintain, if not increase, the coverage of influenza flu,’ ‘Penttinen said.

The southern hemisphere escapes the flu shot can perhaps make one more blind spot: Less circulating flu virus means less clues as to which genetic variants are most prevalent and likely to contribute to the next flu season. The current record low season is creating a genetic bottleneck, McCauley says, and the flu variants that survive “will probably be the fittest,” he says. It is not clear which variants will dominate if flu inevitably hits the head again.

Barr and McCauley, whose institutions are two of six that collect and analyze flu samples to decide next year’s vaccine composition, say they have received fewer patient samples than in previous years.

Insufficient data could lead to a less effective vaccine for the Southern Hemisphere in 2021. The contents of that cocktail should be decided by the end of September. “It’s a little annoying,” Barr says, “but we will do the best we can with the viruses we have.”