RSV Season 2023

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Last reviewed
September 14, 2023
Content Overview
Respiratory syncytial virus outbreaks are seasonal in 2023

RSV Season September 2023

Globally, respiratory syncytial virus (RSV) activity was found to be generally low, reported the World Health Organization (WHO) Influenza Update N° 453. As of September 4, 2023, RSV activity was generally low globally except in some parts of Western Australia and some Central and South American countries.

The U.S. Centers for Disease Control and Prevention (CDC) RSV detection graphs display the 5-week moving average in the U.S. The CDC observed increased RSV activity in parts of the Southeastern United States as of September 5, 2023. The weekly percentage of positive detections reported to the National Respiratory and Enteric Virus Surveillance System (NREVSS) has remained below the season onset threshold of polymerase chain reaction (PCR) test positivity of 3% for two consecutive weeks.

The RSV-NET Interactive Dashboard shows for the 2022-2023 RSV season in the U.S., the overall rate of related hospitalizations was 50.9 per 100,000 people. The U.S. CDC Morbidity and Mortality Weekly Report presented the seasonality of RSV in the U.S. from 2017–to 2023. The 2022–2023 RSV season onset occurred in June, and the proportion of positive PCR results peaked in November, suggesting a return toward prepandemic seasonality. A study published in February 2022 found that RSV showed less variability in annual mortality rates over 19 seasons but had marked geographical variation among those at different ages.

A study published by PLOS Medicine on July 17, 2023, concluded that the RSV disease burden is high, especially in the nearly 600 million children under five living in 121 low-income and middle-income countries. The peak age of community-based RSV incidence is 4.8 months, and the mean and median age of infection are 18.9 and 14.7 months, respectively. These results suggest that the ideal prophylactic strategy may require multiple products to avert the risk among preschool children, wrote these researchers.

RSV Season in the Americas

The Pan American Health Organization (PAHO) published an Epidemiological Alert for week 34 on September 1, 2023, confirming RSV activity has remained low. It has shown a decrease in the last weeks but remains at medium-high levels of circulation. On May 23, 2023, an updated Protocol and Technical note regarding RSV laboratory diagnosis. SARInet updates the seasonality of RSV in Latin America and the Caribbean. 

RSV Season Australia

As of August 20, 2023, Australia's Department of Health and Aged Care published report #10, Influenza-like-illness activity in the community has remained stable in the last fortnight. The number (1,652) and proportion of RSV notifications by age group and reporting period since January 2023 are linked here. As of mid-July 2023, American Samoa is no longer on high alert for RSV.

RSV Season Canada

RSV season in Canada is typically from October until May, with most cases occurring in winter. Up-to-date RSV detection information in Canada for week 34 is posted at this link, including positive RSV tests in Canada by region by surveillance week.

RSV Season Florida 2023

Across both prepandemic and pandemic years, RSV circulation in the U.S. began in Florida, then the southeast, and later in the north and west regions. Florida's RSV season is longer than the rest of the U.S. and has distinct regional patterns, says the U.S. CDC. The Florida Department of Health segmented reports into five RSV regions, each with its own RSV season; as of week #36, September 9, 2023, RSV activity in Florida was increasing admission, positivity, and emergency room rates, and two previous outbreaks, but no current RSV outbreaks. However, NREVSS data show increases in weekly PCR positivity in Florida as of September 7, 2023; the 3-week moving average of PCR positivity was 7.63.

RSV Season Georgia

The CDC's HAN CDCHAN-00498 has observed increased rates of RSV-associated hospitalizations in Georgia reported to RSV-NET. Among children ages <4 years, RSV-associated hospitalization rates reached seven hospitalizations per 100,000 population for the week ending August 19, 2023, with the majority occurring among infants ages <1 year. 

RSV Season Texas

RSV activity typically begins to increase in Texas in September or October, peaks in the winter, and varies by region (urban/rural). The Number and Percentage of positive antigen tests for RSV in Texas for the 2022-2023 RSV season. Historical data for previous RSV seasons in Texas. Rules for excluding children with respiratory viruses from school and childcare are outlined in the Texas Administrative Code, specifically Rule 97.7 for schools and Rule 746.3603 for childcare. 

RSV Season United Kingdom

The U.K. Health Security Agency reported on August 17, 2023, that the overall positivity for RSV was 0.7%, with the highest positivity in those under five years old at 4.4%. For week #32, emergency department attendance for acute bronchiolitis decreased nationally.

RSV, Influenza, COVID-19 Coinfections

On July 25, 2023, tests revealed that coinfections with two or more respiratory viruses occurred in 1.33% of positive results and .55% of the studied samples. The positivity rates varied by the viruses involved, ranging from .38% in adults for the SARS-CoV-2 (COVID-19) coronavirus and RSV to 2.28% in adults for influenza A and SARS-CoV-2. And a 6% coinfection rate of SARS-CoV-2 and influenza A in non-adults.

RSV Mortality

The JAMA Network published results from an Original Investigation in 2022 that reported a mean of 6,549 (95% CI, 6140-6958) underlying respiratory fatalities were associated with RSV each year, including 96 (95% CI, 92-99) among children younger than one year. A study published by the Journal of Infectious Diseases determined that RSV-related deaths in infants <1 year peaked at one month, while bronchiolitis and influenza mortality peaked at two months. Over the 20-year study period, RSV, bronchiolitis, and influenza were listed as the underlying causes of death on 932, 1,046, and 52,293 death certificates, respectively. Children <1 year of age accounted for 39% of RSV and bronchiolitis deaths. 

RSV Adults

The U.S. FDA VRBPAC reviewed RSV Epidemiology and Disease Burden in Older Adults on February 28, 2023, presented by Fiona Havers, MD, MHS, FIDSA. On February 23, 2023, the U.S. CDC Advisory Committee on Immunization Practices (ACIP) conducted a digital and real-world meeting on RSV vaccines. Previously, in October 2022, ACIP presented RSV Vaccines for Older Adults led by Camille Kotton, MD. In adults aged 50 years, hospitalization rates for RSV were similar to those associated with influenza as of 2018. However, from 2005 to 2016, the number of recorded RSV-associated deaths increased, primarily due to greater RSV-associated pneumonia deaths among older adults since 2013. Researchers found 405 deaths in adults over 50 over the twelve years.

RSV Children

The U.S. CDC RSV Work Group presented on June 23, 2022 - RSV Virion and Vaccine Products by Natalie Thornburg; Epidemiology of RSV in Children by Dr. M McMorrow. And the ACIP reviewed in February 2023 Maternal/Pediatric presentations led by Sarah S. Long, MD Chair, Maternal/Pediatric RSV Work Group: Nirsevimab for preventing RSV in infants; Jefferson Jones, MD MPH FAAP, Next Steps for the ACIP Maternal & Pediatric RSV Work Group.

RSV Influenza Comparison

The JAMA Network published an Original Investigation on February 28, 2022: Mortality Associated With Influenza and RSV in the U.S., 1999-2018. This study suggests that RSV poses a greater risk than influenza to infants, while both are associated with substantial mortality among elderly individuals. Influenza has sizeable interannual variability, affecting different age groups depending on the circulating virus. A mean of 6549 (95% CI, 6140-6958) underlying respiratory deaths was associated with RSV annually, including 96 (95% CI, 92-99) deaths among children younger than one year. For influenza, there were 10 171 (95% CI, 9652-10 691) underlying respiratory deaths per year, with 23 deaths (95% CI, 19-27) among children younger than one year. 

A study published in 2017 found that adult patients were less likely to be diagnosed with RSV than with influenza (2.3 vs. 8.3%, respectively), were older, and were more likely to be diagnosed with pneumonia, chronic obstructive pulmonary disease, hypoxemia, and bacterial coinfection. Furthermore, in patients with RSV infection, the 20-day all-cause mortality was higher than that for influenza (18.4 vs. 6.7%, respectively). In addition, RSV infection showed a significantly higher risk of death than the seasonal influenza group, with a hazard ratio of 2.32 (95% CI, 1.17–4.58). 

RSV Monoclonal Antibody Therapy

As of September 2023, the RSV monoclonal antibody Nirsevimab was U.S. FDA-approved.

RSV Vaccines

As of September 2023, two RSV vaccines have been approved for older adults in various countries.

Influenza Season 2023-2024

Flu season trends are published by Precision Vaccinations.