Infants whose mothers received an investigational respiratory syncytial virus (RSV) vaccine in pregnancy had fewer antimicrobial prescriptions during their first 3 months of life, a post hoc secondary analysis of a randomized trial found.

Across 11 countries, infants born to mothers assigned to the vaccine arm during pregnancy had a 12.9% (95% CI 1.3-23.1) lower incidence of antimicrobial prescriptions over the first 3 months of life than infants whose mothers were randomized to placebo (133.7 and 148.7 prescriptions per 100 person-years at risk), reported Joseph Lewnard, PhD, of the University of California Berkeley, and colleagues in the Proceedings of the National Academy of Science.

Maternal vaccination against RSV was estimated to prevent 3.6 antimicrobial prescriptions for every 100 infants in high-income countries over the first 3 months of life, and 5.1 courses for every 100 infants in low- and middle-income countries, which represents about one-fifth and one-tenth of total antimicrobial prescribing in this setting, respectively.

“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,” said co-author Ramanan Laxminarayan, PhD, of the Center for Disease Dynamics, Economics & Policy in Princeton, New Jersey. “Our findings that developing and introducing a vaccine against RSV would also help tremendously in the fight against antibiotic resistance should add greater urgency to research and development efforts in this area.”

This analysis used data from a prior randomized trial of an RSV fusion protein subunit vaccine, which did not meet its primary endpoint in protecting infants of vaccinated pregnant mothers against RSV-associated, medically significant lower respiratory tract infections in the first 3 months of life.

Lewnard’s group revisited the data from the prior trial, which took place from December 2015 to May 2018 in sites that spanned nearly every continent, including the U.S. They specifically examined antimicrobial prescriptions during the first 3 months of life, and determined vaccine efficacy (VE) against new courses of antimicrobials. The intention-to-treat analysis was comprised of 3,005 mothers in the vaccine group and 1,573 mothers in the placebo group.

They found that VE against antimicrobial prescriptions associated with lower respiratory tract infections among infants was 16.6% (95% CI 1.4-29.4). Lewnard’s team discovered that lower respiratory tract infections accounted for 69% to 73% of all antimicrobial prescriptions that were prevented by maternal RSV vaccination.

In high-income countries, VE against acute otitis media-associated antimicrobial prescriptions was 71.3% (95% CI 28.1-88.6), though it was not significant in lower- and -middle income countries, the authors added.

They pointed to the 12.9% VE against all-cause antimicrobial prescriptions, noting that even successful, intensive antibiotic stewardship efforts targeted to healthcare providers only reduce all-cause outpatient antibiotic prescriptions by 3% to 6%, and “have proven difficult to implement in a cost-effective manner.”

Limitations to the data include that as a post hoc secondary analysis, it is meant to be hypothesis-generating, since the trial was not powered to determine “effects against antimicrobial prescribing” and analyses were not adjusted for “multiplicity.” The trial also excluded participants with high-risk pregnancies, who could be an important risk group for RSV.

“These findings underscore the relative importance of vaccination as a strategy to control antimicrobial use, in addition to reducing disease burden, and suggest that maternal RSV vaccination could have a quantitatively similar impact to other vaccine programs,” the authors concluded.

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