Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. The respiratory syncytial virus (RSV) fusion (F) vaccine given to pregnant women did not meet efficacy criteria against RSV-associated lower respiratory tract infection in infants compared to the placebo group, but did show evidence of secondary benefits.

2. The RSV F vaccine was shown to have a safety profile similar to the placebo group.

Evidence Rating Level: 1 (Excellent)

Study Rundown:

Respiratory syncytial virus (RSV) is a common cause of infant hospitalization for lower respiratory tract infections. Currently, no RSV vaccine exists for infants in the first 3 to 6 months of life. Passive immunity whereby IgG antibodies transferred from immunized pregnant women to the infants is a potential alternative to boost immunity against RSV. Specifically, antibodies to the RSV fusion (F) protein epitope enabled neutralizing activity through a vaccine. As such, this study examined RSV F vaccine efficacy against RSV-associated lower respiratory tract infection in infants and safety in pregnant women. The study determined the RSV F vaccine had about 39% efficacy and did not meet the criteria for vaccine efficacy. However, secondary outcomes did show a positive signal with regards to hospitalizations with RSV. One limitation of this study was its design, which overestimated the percentage of infants with RSV-associated lower respiratory tract infection. Nonetheless, this study was strengthened by the diverse, large participant population and one-year infant follow-up.

In-Depth [randomized controlled trial]:

This randomized control trial enrolled 4636 patients in a multicenter study from 11 countries. Inclusion criteria consisted of healthy women between the ages of 18 and 40 years of age with low-risk singleton pregnancies. Participants who had undergone another medication or procedure during the trial were excluded. The patients were randomized in a 2:1 ratio to receive the RSV F vaccine or placebo treatment. The vaccine was administered to the pregnant women between weeks 28 and 36 of gestation. The primary outcome was RSV-associated lower respiratory tract infection through the first 90 days of infant life. RSV-associated lower respiratory tract infection was defined as at least one manifestation of a lower respiratory tract infection and a positive RSV test. RSV-associated lower respiratory tract infection occurred in 1.5% (n, 41) of infants in the RSV F vaccine group compared to 2.4% (n, 35) of infants in the placebo group. The vaccine efficacy was 39.4% (97.52% confidence interval [CI], -1.0 to 63.7). Furthermore, the vaccine efficacy against RSV-associated lower respiratory tract infection of any severity declined to 15% over the first 90 days of infant life and then to 12% over the first 180 days. Additionally, hospitalizations for RSV-associated lower respiratory tract infection in the first 90 days happened in 2.1% of the vaccine group and 3.7% of the placebo group (vaccine efficacy, 44.4%; 95% CI, 19.6 to 61.5). Finally, 40.7% of the women in the vaccine group and 9.9% of women in the placebo group reported mild local injection-site reactions (P<0.001). Besides the reaction, the safety profile for adverse events between the groups was similar. In the infants, events coded as “pneumonia” were less common in the vaccine group (2.2%) compared to the placebo group (4.5%) through 364 days. Taken together, the RSV F vaccine did not meet the vaccine efficacy criteria against RSV-associated lower respiratory tract infection in infants.

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