In clinical trials of the three licensed and recommended RSV vaccines, Arexvy (GSK), Pfizer (Abrysvo), and mResvia (Moderna), mild, local injection site reactions (redness, swelling), fatigue, muscle aches, and headache were common.
In the clinical trials of both RSVPreF3 (Arexvy, GSK) and RSVpreF (Abrysvo, Pfizer) vaccines, a small number of inflammatory neurologic events, including GBS, were reported after RSV vaccination. Further FDA studies presented to the ACIP in October 2024 suggest a small increased risk of GBS of a similar magnitude for both products, approximately 7-9 excess cases per 1 million doses given. No cases of GBS or other inflammatory neurologic events were reported after mRNA RSV (mResvia) vaccination during the clinical trials. CDC and FDA continue to actively monitor the safety of all of these vaccines through national safety surveillance systems.
Estimates presented to ACIP in October 2024 comparing the benefit of RSV vaccination in the older adult population for whom it is recommended to the small increased risk of GBS following Arexvy or Abrysvo show that vaccination of a million people would prevent thousands more hospitalizations and hundreds more deaths than the small number of GBS cases vaccination may trigger. Because the benefits of preventing RSV in the recommended population far outweigh the potential risk of GBS, no changes to recommendations have been made.
In clinical trials, the vast majority of infants had no side effects detected after nirsevimab (Beyfortus, Sanofi) or clesrovimab (Enflonsia, Merck) administration. For both products, the proportion of infants experiencing side effects was very similar in the intervention and placebo groups.
The most common side effects noted during the clinical trials of nirsevimab were rash occurring within 2 weeks after injection (seen in 0.9% of nirsevimab recipients versus 0.6% of placebo recipients) and injection site reactions (including redness, pain, swelling) occurring within 7 days after injection (0.3% of nirsevimab recipients versus 0% of placebo recipients).
Similar reactions were seen with clesrovimab. Rash was seen within two weeks after injection (2.3% of clesrovimab recipients vs. 1.9% of placebo recipients). Redness or swelling at the injection site each were reported in fewer than 4% of clesrovimab recipients, with a similar proportion of placebo recipients also reporting these side effects. See the product package inserts for more details.
Adverse reactions occurring after administration of nirsevimab (Beyfortus, Sanofi) alone or clesrovimab (Enflonsia, Merck) should be reported to MedWatch online (www.fda.gov/medwatch), by fax, by mail, or by contacting FDA at 1-800-FDA-1088.
Adverse reactions occurring after the coadministration of nirsevimab or clesrovimab with a vaccine should be reported to the Vaccine Adverse Event Reporting System (VAERS) https://vaers.hhs.gov, and reports should specify that the patient received nirsevimab or clesrovimab on the VAERS form.
Yes. V-safe is a vaccine safety monitoring system that lets recipients of certain new vaccines share with CDC how they feel after vaccination by receiving and responding to a series of periodic text messages. This is a voluntary system, and individual recipients must register to participate V-safe. V-safe is available to Arexvy (GSK), Abrysvo (Pfizer), and mResvia (Moderna) recipients. For information, or to register, visit CDC’s V-safe website at: www.cdc.gov/vaccine-safety-systems/v-safe/index.html.