Will Nonpharmaceutical Interventions for COVID-19 Mean More Flu Next Year?

The holidays are fast approaching and with cold weather moving across the United States, the soaring case counts are likely to only grow. We are currently seeing unprecedented transmission in the United States and it is unlikely to slow anytime soon without drastic measures. COVID-19 prevention strategies—a topic we’ve all been focused on since early this year. From masking to distancing to hand hygiene, until a vaccine is development, the non-pharmaceutical interventions are what help us prevent the spread of SARS-CoV-2.

Non-pharmaceutical interventions (NPIs) are not only effective against COVID-19, but also respiratory infections, such as seasonal influenza and respiratory syncytial virus (RSV). Several countries have seen a reduction in seasonal influenza cases this year as a result of communication mitigation strategies.

Researchers in Australia saw a 98% drop in RSV and a 99.4% drop in influenza virus detections in children across western Australia. For seasonal respiratory viruses, like influenza and RSV, these impacts save lives and reduce the burden of infection across not only the community, but also hospitals and public health.

As these two viruses are regularly circulating, a research team recently focused on the impact of the COVID-19 NPIs on the future of these endemic viral infections. While this year has seen a reduction in these endemic infections, what does the future hold for the incidence of seasonal flu and RSV? Utilizing epidemiological models, like a Susceptible-Infected-Recovered (SIR) model, and a variety of scenarios, they studied the impact of NPIs on epidemic cycles of these viruses.

The authors noted that, “major dynamic effects are caused by a buildup of susceptible individuals as NPIs reduce transmission. Longer controls, with a greater reduction in transmission, generally lead to a greater increase in susceptibility and larger resulting outbreaks. For Florida, these outbreaks tend to occur in the summer months, but can occur throughout the year. For Texas, where seasonal transmission peaks in the winter, peak outbreaks occur only in the winter months, with the earliest outbreak in 2022.”

Ultimately, this underscores the importance of integrating sustained infection prevention measures into our very social fabric. It is likely that we might see considerable outbreaks of RSV in the winter of 2021-2022 due to susceptibility, but that doesn’t mean we should accept these future outbreaks.

As the authors emphasized, “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 research team did note that there are potential biases to their study, including the assumption that NPIs resulted in a 20% reduction in cases of RSV and influenza. This range is variable as some countries have seen more success at reducing RSV and influenza due to NPIs, but ultimately the US was the focus of this study, which did see a 61% drop in specimens submitted for influenza testing.

Regardless of the potential for future outbreaks of seasonal influenza and/or RSV, it is important that NPIs continue to be implemented and followed. These efforts are not only effective against such seasonal infections, but also COVID-19, which is currently seeing uncontrolled growth across the United States.