Issue 1813: May 14, 2025

CDC published Interim Evaluation of Respiratory Syncytial Virus Hospitalization Rates Among Infants and Young Children After Introduction of Respiratory Syncytial Virus Prevention Products—United States, October 2024–February 2025 on May 8 in MMWR. A portion of the summary appears below. 

Maternal respiratory syncytial virus (RSV) vaccine and nirsevimab, a long-acting monoclonal antibody, help prevent infant RSV-associated hospitalizations; these products became widely available in the United States during the 2024–25 RSV season. . . .

In this ecologic analysis comparing RSV-associated hospitalization rates among infants aged 0–7 months during 2024–25 with those during pre–COVID-19 pandemic RSV seasons in two surveillance networks, rates during 2024–25 were lower by an estimated 28% and 43%. . . .

In the first RSV season with widespread availability of maternal vaccine and nirsevimab, RSV-associated hospitalization rates among infants were lower than in prepandemic seasons. Effective health care planning is needed to protect infants as early in the RSV season as possible through maternal vaccination during pregnancy or infant receipt of nirsevimab.



Access the MMWR article in HTML or PDF.

Related Links

• CDC: MMWR main page providing access to the MMWR family of publications
• Immunize.org: Vaccines A–Z: RSV (Respiratory Syncytial Virus) main page

On May 9, FDA and CDC recommended not administering the live chikungunya vaccine (CHIK-LA, Ixchiq, Valneva) to individuals age 60 years or older while an investigation of reported serious adverse events (SAEs) proceeds. The reported events include neurologic and cardiac events. This follows ACIP’s vote at its April 16 meeting to recommend adding a precaution to its use in people age 65 years and older after review of the preliminary safety data available at that time.  

As of May 7, 17 serious adverse events, including two that resulted in death, have been reported in people age 62 through 89 years who received Ixchiq globally. Most of these reports involve people with underlying chronic medical conditions. Six cases were reported from the United States. Approximately 80,000 doses of Ixchiq have been distributed globally.

Ixchiq contains a live, weakened form of chikungunya virus and may cause symptoms like those of chikungunya disease. Some reports include events consistent with severe complications of chikungunya disease, resulting in hospitalization; one person died from encephalitis.

FDA will update its benefit-risk assessment for Ixchiq in people age 60 years or older. FDA and CDC will continue to evaluate safety reports for Ixchiq. During this assessment, FDA and CDC recommend a pause in use of Ixchiq in this age group. FDA and CDC will update the public when the agencies complete their evaluation.

A non-live, viral-like particle vaccine (CHIK-VLP, Vimkunya, Bavarian Nordic) was licensed by FDA for use in people age 12 years and older in February 2025. ACIP voted on recommendations for its use at its April 16 meeting; these ACIP recommendations will become official after being formally accepted by the CDC director (or by HHS leadership, in the absence of a CDC director). This has not yet occurred.

Related Links

• FDA: FDA and CDC Recommend Pause in Use of Ixchiq (Chikungunya Vaccine, Live) in Individuals 60 Years of Age and Older While Postmarketing Safety Reports are Investigated (5/9/25)
• CDC Presentation to ACIP: Surveillance for Adverse Events Following Use of Live Attenuated Chikungunya Vaccine and its Use Among Travelers (4/16/25)
• Immunize.org: Vaccines A–Z: Chikungunya main page

Immunize.org updated the references on standing orders templates for infants, children, and adults to remove the reference to Appendix B in the Epidemiology and Prevention of Vaccine-Preventable Diseases (the "Pink Book"). The updated standing order templates include:

• Standing Orders for Administering Hepatitis A Vaccine to Children and Teens
• Standing Orders for Administering Hepatitis A Vaccine to Adults

Related Links

• Immunize.org: Clinical Resources: Standing Orders Templates main page
• Immunize.org: Clinical Resources A–Z main page, where you can filter by topic, vaccine, language, or other criteria
• Immunize.org: Vaccines A–Z: Hepatitis A main page

As of May 8, CDC reported 1,001 confirmed measles cases in 2025, with 93% of the cases associated with 14 outbreaks. North Dakota is the latest state to report confirmed cases. Most (709 of 1,001, 71%) were reported by the Texas Department of State Health Services. A map of 2025 confirmed measles cases, as of May 8, is shown below.



In response to growing measles outbreaks involving more than half of U.S. states, CDC published a suite of new resources for public health, healthcare professionals, and families in communities experiencing a measles outbreak. Resources include infographics for families, images to help clinic personnel identify cases, and a Be Ready for Measles communication toolkit. A quick reference for healthcare professionals provides guidance for caring for patients with measles. Find all these resources on the CDC Measles Cases and Outbreaks page.



Related Links

• CDC: Measles Cases and Outbreaks main page
• CDC: Be Ready for Measles Toolkit
• Immunize.org: Vaccines A–Z: Measles main page
• Immunize.org: Standing Orders for Administering Measles, Mumps, and Rubella Vaccine to Children and Teens (PDF)
• Immunize.org: Standing Orders for Administering Measles, Mumps, and Rubella Vaccine to Adults (PDF)
• Immunize.org: Ask the Experts: MMR (Measles, Mumps, and Rubella) web page

Vaccines are important for animal health. The resources below are helpful references for veterinary vaccination. 



Related Links: 

• American Animal Health Association (AAHA): Vaccination Resources
  • Canine Vaccination Guidelines (2024), with infographic
  • Feline Vaccination Guidelines (2020), with infographic
• American Veterinary Medical Association (AVMA): Vaccination
• American Society for the Prevention of Cruelty to Animals (ASPCA): Vaccinations for Your Pet
• Merck Veterinary Manual, open access, containing sections for:
  • Health professionals: Vaccines and Immunotherapy
  • Health professionals: Vaccination of Exotic Mammals
  • Owners: Pet Owners Overview
• National Association of State Public Health Veterinarians: NASPV Compendia of guidelines
• U.S. Department of Agriculture (USDA), Animal & Plant Health Inspection Service (APHIS): Veterinary Biologics
  • List of Licensed Veterinary Biological Products

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