Photo Credit: Peter Hansen

Study found a decreased risk of any and severe respiratory syncytial virus (RSV) lower respiratory disease in the group that received the vaccine compared to the group that received the placebo, and the vaccinated group had a higher risk of preterm birth than the placebo group.

Evidence Rating Level: 1 (Excellent)

Study Rundown: RSV is a major cause of respiratory tract infections in young children, particularly infants under six months. The virus particularly affects those living in low- and middle-income countries, where interventions are needed. Vaccinations for other viruses have shown to be effective in mothers, thus an RSV vaccine was proposed for maternal use, based on the RSV fusion (F) protein. A phase three trial (RSV MAT-009) was conducted as a double-blind, randomized control trial across 24 countries. The participants were assigned randomly using a 2:1 ratio to receive either one intramuscular injection of 120 µg of RSVPreF3-Mat or the placebo. The primary outcomes included any medically assessed RSV-associated lower respiratory tract disease, and any RSV-associated tract disease in infants between birth to six months of age. The sites in low- and middle-income countries were mainly located in the southern hemisphere, whereas the sites in high-income countries were mainly in the northern hemisphere, making it impossible to understand geographic or socioeconomic factors that could have affected the results. Overall, the risk of any severe RSV-associated lower respiratory tract infection was lower in those receiving the RSVPreF3-Mat than in those receiving the placebo; however, the risk of preterm birth was higher in the RSVPreF3-Mat group comparatively.

Click to read the study in NEJM

In-Depth [randomized controlled trial]: Vaccination protecting against RSV during pregnancy may be beneficial for infants, but there has not been enough data on the vaccine’s safety. Thus, the study’s main focus was the safety of infants between birth and 12 months of age and any or severe medically assessed RSV-associated lower respiratory tract infection in infants between birth and six months. Eligible participants included healthy women between the ages of 18 and 49 years of age with a singleton fetus between the gestational age of 24 weeks and 34 weeks with no known fetal abnormalities. In total, 5,328 pregnant women who met the criteria were vaccinated before enrollment and included in the study, along with 5,233 infants. Of these infants, 3426 were placed in the vaccine group and 1,711 in the placebo group. In the vaccinated group, there were 16 cases of RSV-associated lower respiratory tract infections, whereas in the placebo group, there were 24 cases of the disease (vaccine efficacy, 65.5%; 95% credible interval, 37.5 to 82.0). Also, the vaccinated group reported eight severe, medically assessed RSV-associated lower respiratory infections, while the placebo group reported 14 cases (vaccine efficacy, 69.0%; 95% credible interval, 33.0 to 87.6). Preterm birth occurred in 6.8% of infants in the vaccine group but only in 4.9% of infants in the placebo group (relative risk, 1.37; 95% confidence interval [CI], 1.08 to 1.74; P=0.01). In the vaccine group, 0.4% of infants (13 of 3494) died neonatally, whereas, in the placebo group, 0.2% of infants (3 of 1739) died neonatally (relative risk, 2.16; 95% CI, 0.62 to 7.56; p=0.23). Overall, the group who received RVPreF3-Mat had lower risks of any RSV-associated lower respiratory tract disease and severe RSV-associated lower respiratory tract disease when compared to the placebo group.

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