A studywhich has just been published in the journal JAMA Network Open, describes the epidemiological characteristics of respiratory syncytial virus (RSV) infection in Ontario, Canada, following the COVID-19 pandemic. This is the latest in a series of studies suggesting that something has changed regarding the dynamics of virus circulation and hospitalizations; this information is crucial for knowing how to manage seasonal epidemics.
News from Canada
The Canadian study compared hospitalization rates and characteristics of children under 5 years of age admitted to hospital with RSV infection during three pre-pandemic seasons (2017–2020) and two post-pandemic seasons (2021–2023).
Compared to the pre-pandemic period, the 2021–2022 season peaked slightly earlier (early December instead of mid-December), with comparable hospitalization rates. In contrast, the 2022–2023 season peaked a month earlier with a more than doubling of the number of hospitalizations: hospitalizations increased from around 2,000 to 4,977. In 2022, hospitalizations also occurred in the spring and summer. In 2022–2023, a higher than expected number of hospitalizations was observed, particularly in the 24–59 month age group.
The proportion of intensive care unit (ICU) hospitalizations increased (11.4% in 2021–22 and 13.9% in 2022–23, compared with 9.8% in 2017–18) and the rate of ICU admissions tripled, compared with the pre-pandemic period. No differences were observed in ICU length of stay or severe outcomes (requirement of extracorporeal membrane oxygenation [extracorporeal membrane oxygenation, ECMO]deaths in hospital), but the use of artificial ventilation has increased.
News from the United States
Another one study recently published in the journal Pediatrics highlights the epidemiology of RSV in the United States, based on data collected from seven pediatric hospitals across the country. Data from 2021 and 2022 were compared to data from four pre-pandemic seasons (2016–2020).
Most observations are consistent with the results of the Canadian study. In the four pre-pandemic years, the peak of RSV-associated hospitalizations was recorded in December and January. However, this threshold was reached in July (in 2021) and November (in 2022). Hospitalization rates of RSV-positive patients in 2021 and 2022 were higher than in the pre-pandemic period. In 2022, compared with 2021, the hospitalization rate for children under 2 years of age did not change, while that for children aged 24 to 59 months increased significantly.
In 2022, the proportion of children requiring oxygen treatment was higher, but unlike the other study, the proportion of children on mechanical ventilation or admitted to the ICU was not significantly different from previous years. Of note, in 2022, concomitant respiratory infections were more common in RSV-positive hospitalized children.
News from Italy
« Even in our experience, the epidemiology of respiratory syncytial virus has changed since the pandemic. “, said to Univadis Italia Marta Luisa Ciofi degli Atti, head of the joint unit of Epidemiology, Clinical Pathways and Clinical Risk at the Bambino Gesù Children’s Hospital in Rome. Before the pandemic, RSV infection peaks were often in the late December, early January period. The pandemic, with its lockdown policies, interrupted the typical RSV seasonality: we skipped a season, and in 2021 the season was different from all previous ones, arriving early and peaking in October-November, with a much higher incidence. In 2022, the fall incidence was also higher than in the past, peaking in November, but the number of confirmed infections was close to that of pre-pandemic seasons. The 2023 season also arrived early, so we still do not seem to have returned to the pre-pandemic RSV epidemiology. »
In Canada and the United States, 2022 was marked by an increase in incidence among older children. Cases in children aged 1 to 4 years increased from 24% in 2018 to 30% and from 5.4% to 8.7% in children aged 5 to 9 years “, said Marta Luisa Ciofi degli Atti, adding that ” Children in their first year of life were affected similarly in the pre- and post-pandemic period, while cases in older children increased. It is as if there was a build-up of susceptibility: children who did not get sick in the first year of life during the pandemic got sick later in the post-pandemic period ».
Predicting (and preventing) chaos
The authors of the study noted that, in the years studied, the seasonal peak in RSV infections always occurred 4 to 5 weeks after the week in which the number of hospitalizations doubled or tripled. It’s a curve that climbs very quickly. “, notes the epidemiologist.
« Respiratory syncytial virus infection causes severe clinical symptoms in young children who may require hospitalization and, sometimes, assisted ventilation. The epidemic is condensed in a few weeks and has a disruptive effect on health care systems “, observed Marta Luisa Ciofi degli Atti in her closing remarks, who concluded by looking to the future: ” Prevention through vaccination is a huge opportunity in terms of health gains for young children directly affected, as well as to reduce the impact of seasonal RSV epidemics on hospital pathways. At the national and regional levels, we are working to launch vaccination programs to prevent the circulation of this virus. »
