Weekly hospitalization rates for respiratory syncytial virus, better known as RSV, rose from 0.2 per 100,000 people during the week of September 2, 2023, to 1.3 during the week of October 28, according to the Centers for Disease Control and Prevention’s RSV Hospitalization Surveillance Network (RSV-NET).
Along with the seasonal flu and COVID-19, RSV is one of three respiratory diseases that could comprise another “tripledemic” in the US this winter.
RSV is a virus that can cause cold-like symptoms, including a runny nose, coughing, sneezing, and fever. While the symptoms are typically mild, the illness can become more severe and lead to hospitalization, most commonly in the case of older adults and infants.
Infected people transmit RSV during a contagious window of three to eight days via direct contact, droplets from coughing or sneezing, and surface transmission. The Centers for Disease Control and Prevention (CDC) expects that nearly everyone in the US will be infected with RSV by the age of 2.
RSV is responsible for between 58,000 and 80,000 hospitalizations of young children and between 60,000 and 160,000 hospitalizations of seniors in an average year, the bulk of which happen in the fall and winter. These are estimated to result in between 6,000 and 10,000 deaths among seniors and 100–300 deaths among children younger than 5 annually.
RSV season tends to begin in the fall and peak in the winter, but the CDC also notes that the onset of the COVID-19 pandemic has disrupted seasonal patterns and the start may vary by year.
Last season’s infection peak, the highest on record, came during the week of November 12, 2022.
The RSV-NET tracks RSV-associated hospitalizations across 58 counties in 12 states that participate in the Emerging Infections Program or the Influenza Hospitalization Surveillance Program — covering almost 8% of the US population — to compare trends across demographics and seasons, but the data does not adjust for different testing rates and practices.
The 2022–23 RSV season had the overall hospitalization rates of any season dating back to 2018. The full-season hospitalization rate for the 39-week season was 52.8 people per 100,000, compared to 28.1 during the 2021–22 season.
Children younger than 5 and adults over 65 are the most susceptible to severe RSV cases. During the 2022–23 season, children were hospitalized with RSV-related illness at an overall rate of 605.6 per 100,000, more than 10 times the rate of the general population. People over 65 had a rate of 65.5 hospitalizations per 100,000.
Severe RSV also tends to impact racial demographics at different rates, according to the RSV-NET data. After adjusting for age, non-Hispanic American Indian and Alaska Native people were hospitalized after contracting RSV at a rate of 94.7 per 100,000 people in the 2022–23 season. Hispanic populations also had higher rates than the general population at 58.89 per 100,000. In contrast, while the Asian and Pacific Islander demographic had the lowest full-season rate: 32.89.
Early in the 2023–24 season, Black people have the highest rates of RSV-related hospitalization of any racial group.
The CDC monitors the incidence of positive antigen and PCR tests at participating labs through the National Respiratory and Enteric Virus Surveillance System (NREVSS). The system measures positivity rates as a three-week rolling average.
According to NREVSS, 4.5% of nationwide PCR tests at these participating labs were positive for the week of October 14, 2023. Southeastern states tended to have higher percentages of positive PCR tests for RSV than other regions. The five states with the highest rates were Tennessee (27.3%), Florida (21.8%), Louisiana (21.3%), Texas (20.1%), and Georgia (15.3%).
The CDC notes that in fall 2021 and 2022, RSV increased in the Southeast before ramping up in other regions.
The NREVSS is a voluntary program for labs nationwide, and thus may not be entirely representative of states or regions. Some states also have more labs than others — notably, Tennessee and Louisiana reported their elevated rates with an average weekly test load of under 30. To be included in the reports, a state must have data from at least two labs for 36 of the last 52 weeks.
After the record-high 2022–23 RSV season, the US Food and Drug Administration (FDA) announced the approval of new immunization products available for the 2023–24 season.
In May 2023, the agency approved the first RSV vaccine for those 60 and older. In July, it approved nirsevimab, a monoclonal antibody for infants and some young children with particular vulnerability. And that August, the FDA cleared an RSV vaccine for pregnant people. The CDC recommended immunization for infants and vulnerable young children, pregnant people from weeks 32–36 of pregnancy, and adults over 60, provided they consult with their healthcare providers prior.
However, in late October 2023, the CDC issued a health advisory due to the limited nirsevimab supplies, stating that the manufacturer Sanofi had reported that there were not enough doses to cover all eligible infants during this season.
The agency recommended that medical providers prioritize higher-risk infants for immunization.
Despite available vaccinations for all three "tripledemic” viruses during the 2023–24 season, the CDC expected similar rates of hospitalizations related to RSV, COVID-19, and the seasonal flu as last season.
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