Babies Whose Moms Get RSV Vaccine Need Fewer Antimicrobials

Babies born to moms who were vaccinated against respiratory syncytial virus (RSV) while pregnant appear to need fewer antimicrobial prescriptions than babies of unvaccinated moms, according to a study published online today.

To fight antimicrobial resistance, we need to use fewer antimicrobial drugs, the authors write in Proceedings of the National Academy of Sciences (PNAS).

Dr Kathryn Edwards

"In this study, an RSV vaccine was administered to pregnant women to prevent infection in their infants by the transfer of protective antibody to the infant," Kathryn M. Edwards, MD, a professor of pediatrics and the scientific director of the Vanderbilt Vaccine Research Program at Vanderbilt University School of Medicine in Nashville, Tennessee, told Medscape Medical News. Edwards was not involved in the study.

"The authors investigated the impact of the vaccine on the use of antibiotics in infants during the first 90 days of life," Edwards added in an email. "They found that the use of antibiotics was less in infants born to mothers who received the RSV vaccine than in infants born to mothers who received placebo…They suggest that reducing RSV infection in infants will reduce respiratory infections that trigger antibiotic use."

Senior author Ramanan Laxminarayan, PhD, MPH, director and senior fellow at the Center for Disease Dynamics, Economics, & Policy (CDDEP) in Washington, DC, and his colleagues conducted a secondary analysis of a double-blind, randomized controlled trial at 87 sites in 11 countries on several continents.

Dr Ramanan Laxminarayan

In the original study, which was conducted between December 2015 and May 2018, 3005 maternal participants and 2978 infant participants received the experimental RSV F vaccine, and 1573 maternal participants and 1546 infants received a placebo shot. Baseline characteristics of mothers and infants were well balanced, according to the authors.

In the current study, infants born to mothers who received the RSV vaccine were found to be 12.9% (95% CI, 1.3 - 23.1%) less likely to be prescribed antimicrobials during their first 3 months of life compared with infants whose mothers received placebo. Vaccine efficacy against antimicrobial prescriptions for acute lower respiratory tract infections was 16.9% (95% CI, 1.4 - 29.4%).

During the first 3 months of life, for every 100 infants born, maternal vaccination prevented 3.6 courses of antimicrobials in high-income countries (20.2% of all antimicrobial prescribing), and 5.1 courses in low- and middle-income countries (10.9% of all antimicrobial prescribing).

In addition to finding that lower respiratory tract infections accounted for 69%–73% of all antimicrobial prescribing prevented by maternal vaccination, the researchers found marked vaccine efficacy (71.3% [95% CI, 28.1 – 88.6%]) against acute otitis media-associated antimicrobial prescription in infants in high-income countries.

RSV Vaccine Is "One of Our Best Investments"

RSV, the authors explain, is a major cause of upper and lower respiratory tract infections that develop as a single agent or along with bacterial pathogens.

"With decreases in bacterial pneumonia following the introduction of the pneumococcal conjugate vaccine, a vaccine against RSV represents one of our best investments to lower the burden of respiratory infections in children," Laxminarayan said in a press release.

"These findings are not unexpected because viral infections can trigger bacterial infections such as otitis, and reducing viral infections will reduce bacterial infections," Edwards said. "Also, viral infections are often treated with antibiotics because the provider cannot rule out a bacterial infection."

She acknowledged the value of investigating multiple outcomes but added that "the study was underpowered to assess the full impact of the antibiotics."

"If a more effective RSV vaccine can be designed, the impact on reducing antibiotic use will likely be even greater," Edwards advised. "Also, the vaccine was not highly effective in preventing RSV pneumonia. If it had been more effective, the antibiotic impact would likely have been greater."

The authors acknowledged the study's limitations. "Results of this post hoc secondary analysis should be viewed as hypothesis generating, as the trial was not powered for determination of effects against antimicrobial prescribing, and our analyses were not adjusted for multiplicity," they write, and they joined Edwards in recommending further related research.

First author Joseph A. Lewnard, PhD, declares financial support from Pfizer unrelated to this research, three authors are employees of Novavax, and Laxminarayan has disclosed no relevant financial relationships. Edwards reports funding from NIH, CDC; Consultancy to BioNEt and IBM; membership on Data Safety and Monitoring Boards for Pfizer, Sanofi, GSK, Merck, X-4 Pharma, Roche, and Seqirus. The Bill & Melinda Gates Foundation supported the study.

Proc Natl Acad Sci USA. Published online March 14, 2022. Full text

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