A recent study published in JAMA Network Open described the epidemiological characteristics of respiratory syncytial virus (RSV) infection in Ontario, Canada, after the onset of the COVID-19 pandemic. It is the latest in a series of studies that suggest that virus circulation dynamics and hospitalizations have changed over time. These are crucial pieces of information for managing the seasonal epidemic.
News From Canada
The Canadian study compared hospitalization rates and characteristics of children aged < 5 years who were admitted to the hospital for RSV infection during three prepandemic seasons (2017-2020) and two “postpandemic” seasons (2021-2023).
Compared with the prepandemic period, the 2021-2022 RSV season peaked a little earlier (early December instead of mid-December) but had comparable hospitalization rates. The 2022-2023 season, on the other hand, peaked a month earlier with a more than doubled hospitalization rate. Hospitalizations increased from about 2000 to 4977. In 2022, hospitalizations also occurred in spring and summer. In 2022-2023, more hospitalizations than expected were observed, especially in the 24-59–month-old group.
The percentage of patients hospitalized in intensive care units (ICUs) increased (11.4% in 2021-2022 and 13.9% in 2022-2023 compared with 9.8% in 2017-2018), and the ICU hospitalization rate tripled compared with the prepandemic period. No differences were observed in ICU length of stay or severe outcomes (such as use of extracorporeal membrane oxygenation or hospital mortality). The use of mechanical ventilation increased, however.
News From the USA
Another recent study, published in Pediatrics, provides an overview of RSV epidemiology in the United States based on data collected from seven pediatric hospitals across the country. Data from 2021 and 2022 were compared with those from four prepandemic seasons (2016-2020).
Most observations agree with what was reported in the Canadian study. In the four prepandemic years, the peak of RSV-associated hospitalizations was recorded in December-January. In 2021, it was in July, and in 2022, it was in November. Hospitalization rates of RSV-positive patients in 2021 and 2022 were higher than those in the prepandemic period. In 2022, compared with 2021, the hospitalization rate of children aged < 2 years did not change, while that of children aged 24-59 months increased significantly.
In 2022, the percentage of children requiring oxygen therapy was higher. But unlike in the other study, the percentage of children undergoing mechanical ventilation or those hospitalized in ICUs was not significantly different from the past. It is worth noting that in 2022, multiple respiratory coinfections were more frequently found in RSV-positive hospitalized children.
News From Italy
“In our experience, as well, the epidemiology of RSV has shown changes following the pandemic,” Marta Luisa Ciofi degli Atti, MD, head of the Epidemiology, Clinical Pathways, and Clinical Risk Complex Operating Unit at the Bambino Gesù Pediatric Hospital in Rome, Italy, told Univadis Italy. “Before the pandemic, RSV infection peaks were regularly in late December-January. The pandemic, with its containment measures, interrupted the typical seasonality of RSV: A season was skipped, and in 2021, there was a season that was different from all previous ones because it was anticipated, with a peak in October-November and a much higher incidence. In 2022, we also had a higher autumn incidence compared with the past, with a peak in November. However, the number of confirmed infections approached prepandemic levels. The season was also anticipated in 2023, so prepandemic epidemiology does not seem to have stabilized yet.”
As did Canada and the USA, Italy had an increase in incidence among older children in 2022. “Cases of children aged 1-4 years increased from 24% in 2018 to 30%, and those of children aged 5-9 years from 5.4% to 8.7%,” said Dr. Ciofi degli Atti. “Children in the first year of life were similarly affected in the pre- and postpandemic periods, while cases increased among older children. It is as if there has been an accumulation of susceptible patients: Children who did not get sick in the first year of life during the pandemic and got sick later in the postpandemic period.”