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During last year's respiratory virus season, newly approved vaccines for respiratory syncytial virus (RSV) were effective in preventing associated hospitalizations and more serious outcomes in adults 60 and older, an analysis of electronic health records across eight states showed.

In immunocompetent individuals, adjusted vaccine effectiveness reached 80% (95% CI 71-85) against RSV-associated hospitalizations, 81% (95% CI 52-92) against associated critical illness (intensive care unit [ICU] admission, death, or both), and 77% (95% CI 70-83) against RSV-associated emergency department visits, reported Amanda Payne, PhD, of the CDC, and colleagues.

The vaccines showed a good amount of benefit in higher-risk groups as well, according to the findings in .

In hospitalizations for RSV-like illness among adults with immunocompromising conditions, vaccine effectiveness was 73% (95% CI 48-85). And in the immunocompetent adults, effectiveness against RSV-associated hospitalizations and emergency department encounters was similar regardless of age:

• 60-74 years: 81% and 75%, respectively
• ≥75 years: 79% and 78%

The clinical trials that led to the vaccine approvals "really were not powered to assess RSV vaccine efficacy in these higher-risk populations -- so adults aged 75 and older or adults with immunocompromising conditions," Payne told MedPage Today.

Along with the effectiveness against severe outcomes, "we were also able to show that the vaccines worked well in adults 75 and older and those with immunocompromising conditions," she added.

The real-world data helped inform CDC's updated recommendations around RSV vaccines, and "gave clarity to who would benefit most in terms of receiving a vaccine," said Payne. "Those current recommendations are for all adults 75 and older who have not already received an RSV vaccine dose to receive a dose, and then those 60 to 74 with certain underlying medical conditions, that [those] who have not already received a dose of vaccine, that they would get that dose of vaccine."

In an , Angela Branche, MD, of the University of Rochester Medical Center in New York, said that "what is remarkable is how closely vaccine effectiveness against hospitalization or emergency department encounters matches the clinical trial efficacy estimates against lower respiratory tract disease."

The data also provide an answer to another crucial question: "within-season waning of vaccine-induced protection, which was refuted by similar point estimates at 14-59 days versus at least 60 days after vaccination, with overlapping confidence intervals," Branche wrote.

"It was exactly what was needed to help us understand how effective these vaccines are in a real-world setting," Branche told MedPage Today.

The data allow practitioners to say with confidence, that if a patient has received their vaccine, they are 80% less likely to be hospitalized with RSV, she said.

Branche noted that the study grouped all immunocompromised individuals together.

"Having said that, it was a bit of a surprise that the efficacy was so good among immunocompromised patients," she said. "You might expect somewhat lower efficacy, and that fact that it was fairly similar ... was encouraging and maybe a little bit of a surprise."

The study found that estimates of vaccine effectiveness were similar by product type. At the time of study, only Arexvy and Abrysvo were approved and in use. Since then, a third RSV vaccine has been approved for use in adults: mResvia.

Regarding hospitalizations among immunocompetent older adults, vaccine effectiveness was 83% for the GSK vaccine and 73% for the Pfizer vaccine, Payne and colleagues reported. Vaccine effectiveness was 77% and 79%, respectively, for emergency department visits.

The study looked at 28,271 hospitalizations and 36,521 emergency department visits for RSV-like illness among immunocompetent adults, along with 8,435 hospitalizations for RSV-like illness among adults with immunocompromising conditions.

"Hopefully the data that we show in this paper will help boost confidence that the vaccines will help prevent severe disease," said Payne, "and we'll continue monitoring more in the future."

Limitations included that researchers were unable to rule out the possibility that patients with RSV-positive encounters could have had an encounter for other reasons, "which could have lowered vaccine effectiveness estimates," Payne and colleagues noted.

Additionally, misclassification of vaccine status was possible, there was site-to-site variation in RSV testing, all underlying conditions might not have been captured, and there may have been some residual confounding as some variables are poorly captured in electronic health records (i.e., smoking history), they noted. Also, findings may not be generalizable to the entire U.S. population.

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