CDC Provides Additional Data on RSV Vaccines’ Safety, Rationale on Recommendations

In yesterday’s MMWR, the CDC released its official guidance for RSV recommendations and included safety profiles of each of the approved vaccines. The agency reported on adverse effects and some serious, rare occurrences including Guillain-Barré syndrome (GSB) and immune thrombocytopenia. A rare risk of each was associated with the protein subunit RSV vaccines, which include GSK’s Arexvy and Pfizer’s Abrysvo vaccinations.

Regarding GSB, an analysis was performed reviewing post licensure safety data and an FDA self-controlled case series. “The analysis compared GBS incidence during a risk interval (days 1–42 postvaccination) with that during a control interval (days 43–90 postvaccination),” the investigators wrote. “Among beneficiaries vaccinated before October 8, 2023, the GBS adjusted incidence rate ratio in the risk interval versus the control interval was 2.30 (95% CI = 0.39–13.72) for GSK’s Arexvy and 4.48 (95% CI = 0.88–22.90) for Pfizer’s Abrysvo. In this analysis, GBS cases were identified using medical claims data and were not yet confirmed by review of medical records; a final analysis will incorporate medical record review for confirmation of GBS diagnoses and will include additional adults vaccinated later in the 2023–2024 RSV season.” Still, the CDC authors noted that the initial analysis “did not provide clear, conclusive evidence of an elevated risk for GBS associated with RSV vaccination in older adults, but an elevated risk of GBS could not be ruled out. GBS safety surveillance is ongoing and additional analyses are underway."

Specifically for immune thrombocytopenia (ITP), CDC reported that initially, “the of rapid cycle analysis performed by the Vaccine Safety Datalink demonstrated a statistical signal for immune thrombocytopenia (ITP) in a risk interval (days 1–21) after GSK Arexvy vaccination, without simultaneous receipt of another vaccine, compared with a comparison interval (days 22–42).” However, upon further review of medical records, CDC found the onset of a majority of the cases happened before vaccination and the onset after vaccination occurred in only 4 cases during the risk interval and 1 case during the comparison interval. With the small number of cases, the investigators reported that an association could not be confirmed between the GSK vaccine and ITP.

For the mRNA vaccine, mResvia, which is manufactured by Moderna, investigators did not find any elevated risks for adverse events. “No cases of Guillain-Barré syndrome (GBS), other inflammatory neurologic events, myocarditis, or pericarditis were recorded within 42 days after mResvia vaccination,” the investigators wrote.

It is important to note, the vaccine was FDA approved at the end of May of this year, so the data for post licensure has not be analyzed yet.

Rationale for Recommendations

In discussing the rationale for changing the recommendations from a safety standpoint, CDC acknowledged there was not a full understanding of the pathway of these rare adverse events last year. “The 2023 shared clinical decision-making RSV vaccination recommendation was made in the setting of uncertainty in some portions of the evidence profile. RCTs of both protein subunit vaccines (GSK Arexvy and Pfizer Abrysvo) were underpowered to demonstrate protection against RSV-associated hospitalization or death, and enrolled few participants who were frail or aged ≥75 years," the authors wrote. "Although both vaccines were well-tolerated and exhibited an acceptable safety profile, a small number of inflammatory neurologic events, including GBS, were observed after RSV vaccination in clinical trials. Because of the small number of GBS cases in the trials, it was unclear whether they represented an association between RSV vaccination and GBS or occurred because of chance alone. Acknowledging these uncertainties, in June 2023 ACIP recommended shared clinical decision-making to encourage providers and patients to consider individual risk of RSV disease.”

In thinking about adverse events, CDC encourages vaccine recipients to
report them to the Vaccine Adverse Event Reporting System (VAERS). To submit an adverse event to VAERS, interested parties can go to https://vaers.hhs.gov/index.html or call 1-800-822-7967.

Recommendations

Back in June, the CDC’s Advisory Committee on Immunization Practices (ACIP) met to discuss the vaccine schedule for RSV in seniors and recommended that seniors 75 years of age and older receive the RSV vaccine, and that people ages 60–74 who are at increased risk of severe RSV, meaning they have certain chronic medical conditions, such as lung or heart disease, or they live in nursing homes, receive the RSV vaccine.

“The CDC has updated its RSV vaccination recommendation for older adults to prioritize those at highest risk for serious illness from RSV,” said Mandy Cohen, MD, MPH, said at that time. “People 75 or older, or between 60-74 with certain chronic health conditions or living in a nursing home should get one dose of the RSV vaccine to provide an extra layer of protection.”

“Based on currently available evidence, ACIP concluded that the benefits of RSV vaccination did not clearly outweigh the potential harms in adults aged 60–74 years without risk factors for severe RSV disease,” the authors of the MMWR article wrote. “However, ACIP also stressed that research regarding RSV risk factors is ongoing, so providers should continue to have flexibility in offering RSV vaccine to patients they assess to be at increased risk for severe disease even if they do not fall into an explicitly named risk category.”

Timing of Vaccination

CDC points out that eligible adults can receive the vaccination at any point during the course of the year, but says recipients will receive the greatest benefit from August through October during the RSV season. Also, these recommendations are for adults who did not get an RSV vaccine last year. The RSV vaccine is not currently an annual vaccine.

Reference
1.Britton A, Roper LE, Kotton CN, et al. Use of Respiratory Syncytial Virus Vaccines in Adults Aged ≥60 Years: Updated Recommendations of the Advisory Committee on Immunization Practices — United States, 2024. MMWR Morb Mortal Wkly Rep. ePub: 6 August 2024.
DOI: http://dx.doi.org/10.15585/mmwr.mm7332e1