RSV Cases Surge into Spring: Most States Extend Immunization Deadline for Infants and Toddlers

Respiratory syncytial virus (RSV) is defying seasonal norms this year, surging into late spring and forcing public health officials across the United States to extend immunization deadlines for infants and toddlers. Typically peaking in winter and tapering by March, RSV activity has lingered unusually late, with federal data showing 7.5% of tests positive for the virus during the third week of March—nearly 50% higher than the 5% positivity rate recorded at the same time last year. In response, health departments in 48 states, territories, and major cities have pushed back the deadline for monoclonal antibody immunizations from the traditional March 31 cutoff to at least April 30, a move aimed at curbing hospitalizations as the virus continues to circulate.

• RSV cases are 50% higher than last year’s mid-March positivity rates, signaling an unusually prolonged season.
• 48 states have extended RSV immunization periods through April 30, allowing continued protection for infants and toddlers.
• RSV is the leading cause of infant hospitalization in the U.S., with 2-3 out of every 100 babies under 3 months hospitalized annually.
• Monoclonal antibody shots and maternal RSV vaccines have reduced infant hospitalization rates by up to 80% in recent data.

Why RSV Season Is Lasting Longer Than Usual in 2024

Public health experts are still unraveling the reasons behind this year’s atypical RSV surge, which began later than usual in December and has persisted into spring. While RSV historically follows a predictable seasonal pattern—peaking in winter and declining by spring—2024 has bucked the trend. Several factors may contribute to this shift, including changes in climate patterns that altered indoor gathering behaviors, variations in healthcare-seeking behavior post-pandemic, and possible shifts in viral circulation following the widespread adoption of COVID-19 mitigation measures.

Climate and Behavioral Shifts: How Weather and Habits May Fuel RSV Spread

Dr. Jennifer Nuzzo, an epidemiologist and director of the Pandemic Center at Brown University School of Public Health, suggests that climate variability could play a role. ‘If people are spending more time indoors due to unseasonable weather, that increases opportunities for RSV to spread,’ she explains. RSV, like influenza and other respiratory viruses, thrives in close quarters. Unusually mild winter temperatures or erratic weather patterns may have delayed the typical drop in RSV cases, keeping transmission rates elevated into March and April.

The Role of Immunization Gaps and Viral Evolution

Another factor could be the uneven uptake of RSV immunizations. While monoclonal antibodies and maternal vaccines became available for the first time during the 2022-23 season, vaccination rates have varied widely by region. Some parents may have delayed immunizations due to confusion amid the CDC’s 2024 childhood immunization schedule changes, which recommended fewer routine vaccines for most children. However, the CDC and HHS explicitly maintained their RSV immunization recommendations, reiterating that infants born to unvaccinated mothers should receive one dose of the monoclonal antibody.

“The bottom line is, it’s important that plans to respond to these viruses should be tied to actual disease trends, rather than a calendar on the wall. This is why real-time surveillance is critical—we need to ensure RSV monoclonal antibodies are available for as long as the virus is circulating.” — Dr. Jennifer Nuzzo, epidemiologist and director of the Pandemic Center at Brown University School of Public Health

How RSV Immunization Extensions Protect America’s Most Vulnerable Infants

RSV is no minor cold for infants. The virus is the leading cause of hospitalization among babies under 1 year old in the U.S., with 2-3 out of every 100 infants younger than 3 months requiring hospitalization annually. This season alone, tens of thousands of children have been hospitalized with RSV, straining pediatric wards in hospitals across the country. The monoclonal antibody immunization, marketed as Beyfortus (nirsevimab), has emerged as a game-changer since its FDA approval in 2023.

The Science Behind Monoclonal Antibodies for RSV

Unlike traditional vaccines, which stimulate the immune system to produce antibodies, monoclonal antibodies provide immediate, passive immunity by delivering lab-made antibodies directly into the bloodstream. A CDC study published in 2023 found that hospitalization rates among infants up to 7 months old during the 2023-24 RSV season were 80% lower than in previous seasons without immunization access. For context, RSV-associated hospitalizations among infants cost the U.S. healthcare system an estimated $1 billion annually before these interventions.

The American Academy of Pediatrics recommends monoclonal antibody immunization for all infants under 8 months entering their first RSV season, as well as for high-risk children up to 24 months. Pregnant individuals can also receive the RSVpreF vaccine (Abrysvo) during the 32nd to 36th weeks of pregnancy to pass protective antibodies to their newborns.

“I’ve waited my 30 years in pediatrics to be able to prevent RSV disease in babies. These immunizations are truly game-changers. We should be doing everything possible to ensure every baby is protected from RSV.” — Dr. Michelle Fiscus, pediatrician and chief medical officer for the Association of Immunization Managers

States Take the Lead: How Jurisdictions Are Responding to the RSV Surge

The decision to extend RSV immunization deadlines was driven by state and local health departments, which analyzed regional surveillance data showing persistent virus circulation. The Association of Immunization Managers, coordinating with 66 federally funded immunization programs, found that 48 jurisdictions—covering states from California to Maine—had extended their RSV seasons through April 30 as of late March. This extension allows providers to continue administering monoclonal antibody shots through the Vaccines for Children (VFC) program, a federal initiative that provides free vaccines to eligible children.

States Extending RSV Immunization Deadlines

States extending RSV immunizations through April 30 include Alabama, Alaska, Arizona, Arkansas, Colorado, Connecticut, Delaware, Florida (though Florida has year-round RSV activity), Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri (considering case-by-case orders), Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia (considering case-by-case orders), Washington, West Virginia, Wisconsin, and Wyoming.

States With No Extension or Year-Round Activity

Not all jurisdictions have extended their RSV seasons. Ten states and territories—including Hawaii, Louisiana, Oregon (which has year-round RSV activity), and Washington, D.C.—have elected not to extend the deadline. Louisiana cited low current RSV activity, while Washington, D.C., noted that its data did not support an extension. Missouri and Virginia are taking a different approach, allowing providers to determine on a case-by-case basis whether to administer immunizations beyond March.

Public Health Experts Warn Against Underestimating RSV’s Threat

Despite its common cold-like symptoms in healthy adults, RSV can be devastating for infants, older adults, and immunocompromised individuals. The virus leads to approximately 58,000 hospitalizations among children under 5 each year in the U.S., according to CDC estimates. Globally, RSV is responsible for an estimated 3.6 million hospitalizations and 100,000 deaths annually among children under 5. In 2023, the World Health Organization declared RSV a global health priority, emphasizing the urgent need for widespread immunization.

Regulatory Oversight and Safety Concerns Amid Immunization Rollout

While the CDC and FDA have repeatedly affirmed the safety and efficacy of RSV monoclonal antibodies and maternal vaccines, the rollout has not been without scrutiny. In mid-March, the CDC launched inquiries into reports of adverse events, including rare cases of severe allergic reactions. As of April 2024, the CDC reports that over 1.5 million doses of Beyfortus have been administered in the U.S. with no confirmed cases of anaphylaxis linked to the immunization. The agency continues to monitor data closely.

The Economic and Social Cost of RSV Hospitalizations

The financial burden of RSV hospitalizations is staggering. A 2022 study published in *Pediatrics* estimated that the average cost of an RSV hospitalization for a child under 5 is $14,500, with total annual costs to the U.S. healthcare system exceeding $1 billion. Extended hospital stays—often lasting 3-7 days for severe cases—also place emotional and logistical strain on families. In rural areas, where pediatric beds are scarce, RSV surges can overwhelm local hospitals, leading to transfers of critically ill infants to larger medical centers.

What’s Next? Balancing Seasonal Trends and Public Health Preparedness

Public health officials emphasize that the extension of RSV immunization deadlines is a temporary measure tailored to this season’s unique circumstances. Looking ahead, experts are calling for improved real-time surveillance systems to detect shifts in viral circulation patterns more quickly. ‘We can’t rely on historical trends alone,’ says Dr. Tao Sheng Kwan-Gett, Washington state’s health officer. ‘We need to be agile, using data to guide our response rather than rigid seasonal calendars.’

How Parents and Caregivers Can Protect Infants from RSV

For parents of infants and young children, the extended immunization window is a critical opportunity to reduce risk. The CDC recommends the following steps:

• Infants under 8 months entering their first RSV season should receive one dose of Beyfortus (nirsevimab) before or during the RSV season.
• Pregnant individuals should ask their healthcare provider about receiving the RSVpreF vaccine (Abrysvo) during the 32nd to 36th weeks of pregnancy.
• Avoid close contact with sick individuals, and practice good hand hygiene to reduce transmission.
• Keep infants away from crowded indoor spaces, especially during peak RSV activity.
• Monitor for symptoms such as difficulty breathing, wheezing, or dehydration, and seek medical attention if they arise.

Key Takeaways: Why This RSV Season Matters

• RSV activity this year is 50% higher than last year’s mid-March rates, with 7.5% of tests positive—a sign of an unusually prolonged season.
• 48 states have extended RSV immunization deadlines through April 30, allowing continued protection for infants and toddlers as the virus circulates.
• Monoclonal antibody immunizations have slashed infant hospitalization rates by up to 80% in early data, making them a critical tool in preventing severe illness.
• Public health experts warn that RSV remains a leading cause of infant hospitalization, with significant economic and emotional costs.
• Real-time surveillance and adaptive public health strategies are essential to managing RSV and other respiratory viruses in the post-pandemic era.

Frequently Asked Questions About RSV Immunization Extensions