Respiratory syncytial virus (RSV) is responsible for many respiratory hospital admissions in winter, particularly early in life. In Aotearoa New Zealand, measures taken in 2020 to eliminate COVID-19 also eliminated RSV transmission.

Our study looked at the impact of RSV return in 2021 and 2022. We found a sharp increase in weekly cases in 2021, with a peak 16 times the pre-COVID rate in the high-risk infant age group. However, a similar proportion of cases were admitted to ICU, suggesting no change in individual severity but a potentially overwhelming burden on the healthcare system. Consistent surveillance methodology makes it likely that these increases resulted from an RSV immunity gap.

In 2022, we saw reduced admissions and ICU admissions rates across most ages, possibly due to high circulating immunity from the 2021 season. This protection may have sheltered the health system from an overwhelming ‘triple-demic’ as seen in other nations where RSV, influenza and COVID-19 had coalescing peaks.

New Zealand does not have funded RSV immunisations routinely available for infants, as seen in Australia, Europe and the US/Canada. Such protection could provide more widespread immunity - as seen in 2022 - without intense waves of infection.