When respiratory virus season starts, it’s usually pretty predictable. Patients begin to be admitted to hospitals with influenza or respiratory syncytial virus (RSV) around October in the Northern Hemisphere. Thousands of people fall ill and many die, but apart from the odd extreme year, health systems across Europe and North America are not usually at risk of being overwhelmed. But the pandemic has derailed that predictability. Add another virus to the seasonal mix and the flu and RSV are back this year with a vengeance. A “twin” or even “triplidemia” could be on the way, with all three viruses striking at once, diseases soaring and health systems creaking under the strain. There are already signs that this is happening. Many hospitals in the US are at capacity, caring for large numbers of children infected with RSV and other viruses, many more than would be expected at this time of year. The US Centers for Disease Control and Prevention (CDC) does not track RSV cases, hospitalizations and deaths as it does for the flu, but hospitals across the country have reported peak levels typically seen in December and January. Almost one in five PCR tests for RSV were positive in the week ending October 29, with that rate doubling over the course of a month. In general, the higher the percentage of tests that come back positive, the more common a virus is in the wider community. In the three years before the pandemic, an average of just 3 percent of tests came back positive in October. This is a hangover from the pandemic. Over the past two years, RSV and influenza have been contained thanks to the protective measures people have taken against the coronavirus: wearing masks, washing hands, and isolating themselves. Between the start of the pandemic and March 2021, the weekly positivity rate for RSV tests remained below 1 percent, according to the CDC — below where it was in pre-pandemic times. In July this year, health experts warned in The Lancet that the benefits of these pandemic precautions could end up backfiring this winter. Reducing exposure to common endemic viruses such as RSV and influenza, experts argued, risked creating an “immunity gap” in people who were either born during the pandemic or had not previously developed sufficient immunity to those viruses. This prediction now appears to be coming true, as children contract these viruses for the first time, without having built up any previous immunity, and become seriously ill. “We’re seeing kids at older ages getting RSV who would have previously gotten it at a younger age,” says Rachel Baker, an assistant professor of epidemiology at Brown University in Rhode Island, who co-authored the Lancet commentary. “That puts some pressure on hospitals.”
