When do Respiratory Syncytial Virus (RSV) infections typically peak?

RSV Infection Peaks

In the United States, RSV infections typically peak in January or February, with the season generally running from November through March in most regions. 1

Seasonal Timing in the United States

The American Academy of Pediatrics guidelines provide clear seasonal patterns for RSV circulation:

• Season onset: RSV outbreaks usually begin in November or December 1
• Peak activity: January or February represents the typical peak of RSV infections 1
• Season end: The RSV season typically concludes by the end of March or sometime in April 1
• Median season duration: 15 weeks nationally, with regional variation from 13 to 23 weeks 1

Regional Variation Within the United States

Geographic location significantly influences RSV timing, with a clear north-to-south gradient:

• Southern United States: Experiences the earliest onset of RSV activity 1
• Midwestern states: Tend to experience the latest onset 1
• Western and Northeast regions: Seasonal timing falls between the South and Midwest patterns 1

Special Geographic Considerations

• Florida: Shows substantial variation in onset and offset dates across different regions within the state, requiring local surveillance data for optimal timing of prophylaxis 1
• Alaska: Experiences higher RSV hospitalization rates and a longer RSV season, particularly in remote regions and among Alaska Native populations 1

Recent Pandemic-Related Disruptions

The COVID-19 pandemic significantly altered typical RSV patterns, though recent data suggest a return to historical seasonality:

• 2020-21 season: The typical winter RSV epidemic did not occur 2
• 2021-22 season: Began unusually early (May), peaked in July, and ended in January 2
• 2022-23 season: Started in June and peaked in November—later than 2021-22 but earlier than prepandemic seasons 2
• Current trend: The 2022-23 season timing suggests seasonal patterns are returning toward prepandemic norms, though off-season circulation may continue 2

International Patterns

RSV seasonality varies by hemisphere and climate:

• Northern Hemisphere: RSV circulates predominantly between November and March 1
• Tropical climates: RSV peaks during the hottest months and rainy season rather than following winter patterns 3, 4
• Temperate climates: Predictable winter peaks occur consistently 3, 4

Clinical Implications for Prophylaxis Timing

Understanding peak timing is critical for optimal administration of preventive interventions:

• Palivizumab initiation: The first dose should be administered before the RSV season starts, typically in November, to provide protection when exposure risk is highest 1, 5
• Monthly dosing: Five monthly doses provide more than 20 weeks of protective antibody concentrations, covering most seasonal variation 1
• Seasonal administration: CDC recommends maternal RSVpreF vaccination during September through January in most of the continental United States 1
• Maximum benefit: Prophylaxis provides greatest benefit during peak season, not during periods of low RSV incidence 1

Surveillance Recommendations

The Centers for Disease Control and Prevention emphasize suspecting RSV during seasonal outbreaks, typically December through March in the Northern Hemisphere. 6 Clinicians should maintain awareness that year-to-year variation occurs within the same community and between communities in the same region, even though the overall pattern remains predictable 1