This winter is unlike the first two pandemic winters, with all common respiratory viruses back in full gear. With many people coming down with the flu, respiratory syncytial virus and/or COVID-19, chatter about "immunity debt" has persisted for months.
The problem many experts have with this concept — or the idea that the influx of flu and RSV that we're seeing now is due to a lack of exposure amid widespread masking and distancing during the last two respiratory virus seasons — is that there is no universal agreement on what "immunity debt" actually means. Many researchers and immunologists also say the idea of viewing the immune system as a muscle that gets weaker without use is dangerous.
The "immunity debt" or "immunity gap" concept became more well-known and spread across social media after French scientists published a paper in May expressing concern there would be an infection rebound among kids who weren't exposed to common pathogens during the pandemic, or who didn't complete routine childhood vaccinations, according to a Dec. 15 report from The Washington Post. The researchers implied that purposeful exposure to pathogens would then keep the immune system stronger.
"Idiocy," Colin Furness, PhD, an epidemiologist at the University of Toronto, said in a Nov. 5 tweet referring to immunity debt, according to the Post. "How did such a nonsensical idea take hold? … The immune system isn't anything like a muscle."
In November, National Nurses United released a statement condemning the notion that the RSV surge was due to children's lack of exposure amid masking and stay-at-home orders, calling "immunity debt" a "flawed conjecture that is not based on science." NNU also called out the CDC for promoting the idea of immunity debt.
"Claiming that children need to become infected to clear their 'immunity debt' provides little benefit to children, ignores individual risks for severe infections (particularly among immunocompromised children), and disregards the science about the virus," the group said.
Instead, they pointed to the lack of public health protections and the effects of earlier COVID-19 infections and long COVID-19 as contributors to the severe RSV season.