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First results: effectiveness of a vaccine against the virus that causes the highest number of hospitalizations in infants tested

The serum that seeks to prevent severe cases of bronchiolitis in infants passed phase 4; it was incorporated into the national calendar last December.

The study showed that the vaccine is 72.7% effective in preventing hospitalizations in infants under three months of age- Shutterstock

This is good news for newborns. The vaccine against respiratory syncytial virus (RSV), which was incorporated into the national calendar in December last year, has just passed phase 4, which is the stage in which the effectiveness of the vaccine is evaluated in the real population. Thus, through a follow-up of babies who had been immunized intrauterine (the mother receives the vaccine during pregnancy), they had fewer severe cases of bronchiolitis during the winter and also fewer hospital admissions than those who did not receive the serum.
This is highly relevant data, since when the vaccine was included in the official calendar, many mothers and specialists had certain doubts when it came to recommending the vaccine, while waiting for the approval of phase 4. On the other hand, among the monitored population, those who were not vaccinated via the mother's side had more complicated symptoms, had to be hospitalized more frequently and, in three cases, even died.
It should be recalled that bronchiolitis, the disease caused by RSV, is the main cause of hospitalizations, pneumonias and deaths due to infectious diseases among infants. The study showed that the vaccine is 72.7% effective in preventing hospitalizations of infants under three months of age due to Acute Respiratory Infections (ARI), a group of diseases that affect the nose, throat and ears, which can reach the lungs. It also showed 86% effectiveness in children under six months of age and 73.9% in hospitalizations due to severe cases in this age group.
Last December, Argentina became one of the first countries in the world to incorporate the RSVpreF vaccine to the national calendar. As of last March, it began to be applied nationwide to reduce the burden of RSV-related diseases in infants. Coverage of the vaccine was not so high: only 62% of pregnant women who had the vaccine indicated were vaccinated . However, it is believed that this number could now increase. With the approval of phase 4 of the vaccine, it is expected that other countries will decide to include it in their schedules as well. And more women and obstetricians will be encouraged to indicate it.
To reach this point, the results of the 2024 RSV season were analyzed, based on a multicenter study of cases and negative test controls, designed by the company iTrials, the Science Team and the Innovation in Health and Equity Policies hub of the National University of San Martín (Unsam) and the Pfizer laboratory, which provided the funding.

Stages

Vaccines go through several phases before they are used. The first two are research phases. The third is where its efficacy is demonstrated in a limited and controlled group of volunteers. There, this vaccine had performed well. But phase 4 was pending, which is when the use of the vaccine is effectively tested in the general population.

"This study measures how efficacy becomes effectiveness. And it has had very good results, reducing the number of serious cases and hospitalizations in infants. This is very good news, because knowing the effectiveness, more mothers will be encouraged to apply this vaccine, as well as more professionals to prescribe it. Furthermore, it is key scientific evidence for decision-makers in other countries to incorporate it into their calendar", explains Gonzalo Pérez Marc, a physician at I-Trials who, together with Analía Rearte (former national director of Epidemiology and currently in charge of the so-called Hub for Innovation in Health Policies and Equity at Unsam), was in charge of the pharmacovigilance of the vaccine.

Gonzalo Pérez Marc, principal investigator of the study - Courtesy of Hospital Militar Central

To pass Phase 4, the vaccine was subjected to the "Berni study". Its objective was to estimate the effectiveness of serum (EV) RSVpreF in preventing hospitalizations due to RSV-associated ARIB and severe ARIB in infants under six months of age, during the first season of the virus after the implementation of the vaccination program.

The Berni study measured the effectiveness of the vaccine in the real world, and was conducted between April and September in 12 hospitals, including public, private and social security centers in six provinces. Data were collected from medical records, epidemiological surveillance and hospital statistics. The study included infants under six months of age hospitalized for ARIB and tested for RSV. In total, 505 infants were evaluated, of which 286 were RSV positive cases and 219 were negative controls.

"The results demonstrated the high effectiveness of the vaccine in preventing hospitalizations due to ARIB and severe ARIB associated with respiratory syncytial virus during the first six months of life," explains Pérez Marc.
So far, it has not been shown to be effective in reducing contagion and mild forms of the disease. However, according to the specialist, it has shown a 50% reduction in the number of consultations in the emergency room for bronchiolitis.

The work has not yet been published, but will be published in the coming months in an international scientific journal to generate scientific evidence and achieve peer review, says Pérez Marc.

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