How will COVID-19 affect the coming flu season? Scientists struggle for clues – Science Magazine

Fearing that a combination of seasonal influenza and COVID-19 will overwhelm hospitals, many countries are stepping up campaigns to increase flu vaccination.

By Kelly ServickAug. 14, 2020 , 4:30 PM

Sciences COVID-19 reporting 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 South Africas National Institute for Communicable Diseases (NICD) set up a plan to learn from the double whammy. They hoped to study interactions between seasonal respiratory viruses and SARS-CoV-2, which causes COVID-19. Does infection with one change a persons risk of catching the other? How do people fare when they have both?

But the flu seasonand the answersnever came. NICDs Centre for Respiratory Disease and Meningitis, which Cohen leads, has logged only a single flu case since the end of March. In previous years, the countrys surveillance platforms have documented, on average, about 700 cases during that period, Cohen says. Weve been doing flu surveillance since 1984, and its unprecedented.

Some cases probably got overlooked as clinics temporary closed and people with mild symptoms avoided medical offices and clinics, Cohen says. But I dont believe it possible that weve entirely missed the flu season with all of our [surveillance] programs. Apparently, travel restrictions, school closures, social distancing, and mask wearing have all but stopped flu from spreading in South Africa. Similar stories have emerged from Australia, New Zealand, and parts of South America.

The Northern Hemisphere hopes to be so lucky. Few cases in the south might mean little infection spreading north, says Pasi Penttinen, head of the influenza and respiratory illness program at the European Centre for Disease Prevention and Control (ECDC). But if lockdowns and social distancing measures arent in place in October, November, and December, flu will spread much more readily than it has in the south, warns virologist John McCauley, director of the Worldwide Influenza Centre at the Francis Crick Institute.

The prospect of a flu season during the coronavirus pandemic is chilling to health experts. Hospitals and clinics already under strain dread a pileup of new respiratory infections, including influenza and respiratory syncytial virus (RSV), another seasonal pathogen that can cause serious illness in young children and the elderly. In the United States, where some areas already face long waits for COVID-19 test results, the delays could grow as flu symptoms boost demand. The need to try to rule out SARS-CoV-2 will be intense, says Marc Lipsitch of the Harvard T.H. Chan School of Public Health.

Because the Southern Hemisphere has largely been spared, researchers have little evidence about how COVID-19 might influence the course of a flu outbreak. One big concern is coinfectionpeople getting COVID-19 and flu at once, says Ian Barr, deputy director of the World Health Organization Collaborating Centre for Reference and Research on Influenza in Melbourne, Australia. Two or three viruses infecting you are normally worse than one, he says.

But the consequences of coinfections with SARS-CoV-2 havent 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, most often rhinoviruses and enteroviruses that cause cold symptoms, as well as RSV. Only one of the patients had influenza, although there likely wasnt much flu circulating so late in the U.S. season, says Stanford pathologist Benjamin Pinsky, a co-author. The study didnt find a difference in outcomes between COVID-19 patients with and without other infections. But it was too small to draw broad conclusions.

COVID-19 control measures dramatically reduced transmission of flu in many Southern Hemisphere countries this season.

FluNet; Global Influenza Surveillance and Response System

To make things more complicated, having one virus can change a persons chance of getting 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 show up concurrently or at separate times, such as theirtendencies to wax and wane with the seasons.Coinfections with flu and other respiratory viruses are relatively rare, Nickbakhsh says, and the interactions her group has documented between flu and other viruses have suggested protective effects. For example, being infected with one type of flu virus, influenza A, seemed to reduce the chance of also having a rhinovirus, the researchers reported in 2019. (The mechanism behind this effect isnt yet clear.)

Nickbakhsh is more concerned about RSV, which her team found to have positive interactions with CoV-OC43, a coronavirus species of the same genus as SARS-CoV-2. Its possible, she says, that having COVID-19 could increase a persons susceptibility to RSV, or vice versa. Pinning down 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 fluCOVID-19 combination tests developed by Qiagen, BioFire Diagnostics, and the U.S. Centers for Disease Control and Prevention (CDC).

The impending winter in the Northern Hemisphere has also brought new attention to flu vaccines, which may keep hospital admissions down as health systems grapple with the pandemic. Flu vaccine manufacturers including GlaxoSmithKline and AstraZeneca have announced production increases for the 202021 season. CDCexpects to have a record-setting 194 million to 198 milliondosesa 20 milliondose increase from last year. Last month, the United Kingdoms National Health Service announced it would expand the age groups eligible for a free flu shot among both children and adults.

But what if the flu season is minor? Pouring resources into an immunization campaign necessarily subtracts 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 adds. (Rates among older adultsthe target population for the flu vaccine in many countriesrange from 2% to 72.8%, depending on the country, according tothe most recent ECDC data, released in 2018.) I think the tendency is to say, We should err on the side of cautionputting efforts into at least maintaining if not increasing the influenza vaccine coverage, Penttinen says.

The Southern Hemisphere dodging the flu bullet might create even one more blind spot: Less circulating influenza virus means fewer clues about which genetic variants are most prevalent and likely to contribute to the next flu season. The current record-low season creates a genetic bottleneck, McCauley says, and the flu variants that survive will be presumably the fittest ones, he says. Its not clear what variants will dominate when flu, inevitably, rears its head again.

Barr and McCauley, whose institutions are two of the six that collect and analyze flu samples to decide the composition of the next years vaccine, say theyve 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 must be decided by the end of September. Its a little unsettling, Barr says, but well do the best we can with the viruses that we have.

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How will COVID-19 affect the coming flu season? Scientists struggle for clues - Science Magazine