Skip Navigation LinksEarly-Respiratory-Syncytial-Virus-Activity-and-Use-of-RSV-Prevention-Products Early Respiratory Syncytial Virus (RSV) Activity and Use of RSV Prevention Products

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State of California—Health and Human Services Agency
California Department of Public Health

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TO: Healthcare Providers
Early Respiratory Syncytial Virus (RSV) Activity and Use of RSV Prevention Products

​Key Messages

• During the week ending October 21, 2023, 7.4% of respiratory specimens from sentinel laboratories in California tested positive for RSV[1​​​], indicating an early start to the RSV season; in pre-pandemic years, this level of activity was generally seen in November or December.  

• The long-acting monoclonal antibody, nirsevimab (BeyfortusTM), recommended as passive immunization to protect infants, is currently in extremely short supply, as described in the October 23, 2023 CDC health advisory and prioritization guidance.  

Maternal RSV vaccine (AbrysvoTM) from 32 to 36 weeks gestational age is an alternative to nirsevimab for protecting infants against severe RSV disease.  Most infants will likely only need protection from either the maternal RSV vaccine or nirsevimab, but not both.  Prenatal care providers should discuss potential nirsevimab supply shortages when counseling pregnant people about prenatal RSV vaccine.  

• CDPH will update VFC providers about nirsevimab supplies via email and via postings to  CDPH is encouraging birthing hospitals, acute care hospitals, and others providing care to neonatal patients to join the VFC Program to ensure newborns get immunized against RSV as supplies increase.​​


On October 23, 2023 the Centers for Disease Control and Prevention (CDC) issued a Health Alert Network (HAN) Health Advisory to provide options and prioritization guidance for clinicians to protect infants from respiratory syncytial virus (RSV) in the context of a limited supply of nirsevimab, a long-acting monoclonal antibody immunization product recommended for preventing RSV-associated lower respiratory tract disease in infants. 

Respiratory syncytial virus (RSV) is the most com​mon cause of bronchiolitis and pneumonia in infants and a cause of severe disease in older adults. 

Figure 1​​: Percentage of RSV detections at clinical sentinel laboratorie​​s — California, 2018–2023 (as of October 21, 2023) 

California RSV Rates Table


For more information about specific recommendations and priorities around the use of RSV prevention products based on age, weight, and other factors, please refer to the CDC Health Alert Limited Availability of N​irsevimab in the United States-Interim CDC Recommendations to Protect Infants from Respiratory Syncytial Virus (RSV) during the 2023-2024 Respiratory Virus Season.​


• CDC: RSV for Healthcare Providers

• CDC HAN:  Limited Availability of Nirsevimab in the United States

• CDC MMWR: Use of Nirsevimab for the Prevention of RSV Disease

• CDPH: RSV webpage

• AAP: Palivizumab Prophylaxis in Infants and Young Children at Increased Risk of Hospitalization for Respiratory Syncytial Virus Infection

• AAP: Nirsevimab Frequently Asked Questions​​​​