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Bronchiolitis vaccine: results show it is effective, but there is a warning sign

The ward at Hospital Pedro Elizalde this year. Bronchiolitis is the leading cause of viral pneumonia in children and every year some 100,000 to 300,000 babies die worldwide. Photo: Juano Tesone

With winter over and spring almost over, the vaccine for pregnant women aimed at preventing hospitalizations for bronchiolitis in newborn babies has just passed its first major test: preliminary data from a Phase 4 study showed 73.9% effectiveness in preventing severe cases of respiratory syncytial virus (RSV) in infants up to six months of age whose mothers had been opportunely immunized.

We are talking about pregnant women who received a vaccine and who, through the placenta, passed neutralizing antibodies to their fetuses, a novelty in the prevention of bronchiolitis in which Argentina has been involved for less than a year.

A few facts help to support the information that follows in these lines. First of all, bronchiolitis is not a cold: it is considered the leading cause of viral pneumonia in children and every year some 100,000 to 300,000 babies die worldwide from this condition. Moreover, it is worth remembering that the confirmation of a non-bacterial infection eliminates the option of antibiotics as an "easy solution". At this point, the vaccinations that are being added to the official calendar take on a sidereal importance.

However, when this dose was added to the mandatory schedule for pregnant women in December, questions were raised from many sides, including obstetricians who (even with the scientific publications in hand) sowed doubts among patients. Was it safe to receive this vaccine?

"The data we obtained and which we are about to send for review for publication proved to be absolutely consistent with what we had already seen in the Phase 3 study," said Gonzalo Pérez Marc, a physician from the company 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 and Equity Policies" at the UNSAM), was in charge of the pharmacovigilance of this drug.

The ward of the Ricardo Gutiérrez Children's Hospital in winter. Bronchiolitis is the leading cause of viral pneumonia in children and every year some 100,000 to 300,000 babies die worldwide. Photo: Juano Tesone

Phase 4 or "pharmacovigilance" is the phase in which drugs are studied "on the street". It does not measure the "efficacy" of the drug or vaccine in the body (a variable which, like "safety", is tested in the previous research phases) but the so-called "effectiveness". That is, how the drug works in the daily life of a certain population. That is, in the "real world", a habitat in which people interact in very diverse and unpredictable ways, resulting in contextual conditions that are absolutely unmanageable for researchers.

In line with these concepts, the so-called "BERNI study" was conducted. It was conducted between April and September of this year with the intention of capturing the first measurements of the initial litter of babies who - if their mothers were vaccinated - were in a position to receive the neutralizing antibodies against RSV through the placenta.

The researchers' bet was that, of the nearly 500 babies analyzed in 12 public and private hospitals in the provinces of Buenos Aires, Córdoba, Río Negro, Salta, Mendoza and Santa Fe, there were, behind, a few pregnant women who between 32 and 36.7 weeks decided to be vaccinated with this dose.

It should be noted that the results released on Monday were not formally published, but according to the researchers in charge, there are four figures that they consider satisfactory and that are also eloquent about the capabilities offered by the vaccine.

The results of the RSV vaccine

As for the vaccine's ability to prevent infants aged 0 to 3 months from being hospitalized for acute respiratory infections (or ARIB), the effectiveness result was 72.7%. At the same time, "if one expands and measures the effectiveness of the vaccine in infants up to 6 months of age, the figure drops to 68%, since the antibodies are lost with time, which is to be expected", explained Pérez Marc.
Meanwhile, if what is measured is the capacity of this dose to prevent babies up to half a year of age not only from being hospitalized but also to prevent bronchiolitis from becoming severe, the effectiveness, according to those responsible for the study, was 73.9%.
The vaccine does not promise to prevent infection, but it does minimize severe cases in the first months of life, which is the stage when newborns have their immune skeleton "under construction".
According to the data provided, of the 505 infants studied, 286 were positive for RSV. Although there were three deaths due to the acute lower respiratory infection that can be caused by this virus, all the cases corresponded to patients whose mothers had not been immunized.

Vaccines with coverage in check

The counterpart of the effectiveness percentages mentioned above is the timid number of pregnant women who, in fact, have been vaccinated against RSV, a fact that is in line with the generalized distrust in vaccines that has been growing for years in the country, and that does not receive any favorable wind from the national level, for example, with appropriate public campaigns.
According to preliminary official data available to Clarín, only 62.5% of pregnant women who have been in the 32 to 36.7 weeks of pregnancy since December (the period of indication for this single-dose vaccine) decided to be vaccinated against RSV.
Optimistic, Pérez Marc considered that this is partly due to the fact that "it is the first season, since the vaccine entered the calendar just before the change of government and began to be administered in March of this year".
"If one thinks about the scarce diffusion it has had and adds that it is a new vaccine that also affects pregnant women, the percentage seems more like an achievement", said the doctor, before recalling that "the vaccine has no contraindications".
"Bronchiolitis is an infection that causes health systems to collapse. Not counting that it can seriously infect older adults, it is believed that for every baby that dies from bronchiolitis in a hospital, another one dies at home", reported Pérez Marc, and closed: "After drinking water, there is no public health strategy in history that has saved more lives than vaccines".

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