Flu And Other Infections Have Dropped, But They May Come Back With A Vengeance

People in PPE suits wiping down seats of a subway to help prevent the spread of COVID-19. Image credit: Gukzilla/Shutterstock.com

We’ve got good news and bad news. Thanks to COVID-19 prevention measures, the 2020-2021 flu season appears to be a relatively mild one and many other common illnesses are also down. Unfortunately, it could be a very different situation in years to come and some scientists are bracing for an especially nasty resurgence of infections.

The latest influenza update from the World Health Organization says that levels of flu activity globally are currently much lower than expected for this time of the year. In fact, many parts of the Northern Hemisphere are seeing “below inter-seasonal levels,” indicating it’s lower than levels you’d expect to see in the summer. 

It looks like other common infectious diseases also struggled to get a grip last year too. BioFire has tracked the trends of numerous respiratory pathogens from January 2019 to January 2021 using diagnostic data in the US and created an easy-to-follow chart. At the end of March 2020, the chart shows a sharp slump in the number of infections for adenoviruses, bacterial infections, human metapneumovirus, rhinovirus/enterovirus, influenza A, influenza B, parainfluenza, and Respiratory Syncytial Virus (RSV). Their chart of gastrointestinal pathogen trends also shows a similar pattern for infectious stomach bugs, like norovirus and salmonella. 

Part of the reason may be because fewer infections are being reported as healthcare resources are being swamped with COVID-19. However, it’s also apparent that communicable infections are being given less chance of transmission due to social distancing measures and other COVID-19 control measures.

That’s the good news — and now for the bad news. Some researchers are now looking beyond this past year and are concerned that the world may see a massive bounce-back of many of the infections. So the theory goes, we’ve all spent much of the past year avoiding other people as much as possible, meaning we’ve come into less contact with pathogens and our natural immunity to otherwise common infections may have slipped. 

Forecasting the flu season is notoriously tricky, and predictions of the timing, size, and severity of a seasonal influenza outbreak are not always on the money as it depends on the strain that’s doing the rounds. Nevertheless, some evidence indicates that the weakness of the 2020-2021’s flu season may have consequences for the timing and severity of future outbreaks.

A study, published in November 2020 in the Proceedings of the National Academy of Sciences, looked at the impact of the COVID-19 pandemic on future outbreaks of influenza and RSV. They concluded: “Our results suggest that a buildup of susceptibility during these control periods may result in large outbreaks in the coming years.”

“Substantial outbreaks of RSV may occur in future years, with peak outbreaks likely occurring in the winter of 2021–2022,” the study reads. “Results for influenza broadly echo this picture, but are more uncertain; future outbreaks are likely dependent on the transmissibility and evolutionary dynamics of circulating strains.”

The world is essentially in the middle of a never-before-seen experiment where, after thousands of years of fostering a bunch of different pathogens, many of the circulating bugs have suddenly had their lines of transmission severed. Once social distancing measures are eased, however, it will be open season again. It’s hard to predict exactly how this experiment will pan out, but researchers suggest the world should prepare for the worst.

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