It is the vaccine against bronchiolitis, which is already given free of charge to pregnant women between 32 and 36 weeks. Expectant mothers pass the antibodies to their children and the efficacy against the disease is 80 percent.
Clarín obtained the first official data on the pace of vaccination in the country.
Last year, in the middle of May, the peak of bronchiolitis cases in Argentina was recorded. The disease is caused by the Respiratory Syncytial Virus (RSV) and the novelty is that this year the vaccine has been available since March 1st and has been included in the official vaccination schedule and is therefore free of charge.
According to official data from the Ministry of Health accessed by Clarín, an average of 636 vaccines are administered every day in the country. This represents 42 percent of the births every 24 hours in the country. The figure is encouraging considering that the campaign has just begun.
The figures come from a national survey up to March 11, when 7,082 vaccines had been administered. Of the total, 22 percent corresponds to the province of Buenos Aires -somewhat low considering that its population is 38 percent of the country- and 8.7 percent to the City of Buenos Aires. Santa Fe and Tucumán had vaccinated, according to these first data, more than CABA, with 899 and 772 applications respectively.
The incidence of bronchiolitis in 2024 is, at least at this early stage of the year, almost the lowest in the last decade, with 518.9 cases per 100,000 inhabitants. Only in 2021, a pandemic year, did the statistics place this proportion below, with 396.6 per 100,000. In 2023, at this point, there were 826.7 cases per 100,000.
Infectiologist Gonzalo Pérez Marc is the principal investigator of the phase 3 trial of the RSV vaccine developed by the Pfizer laboratory, a protocol that was carried out at the Central Military Hospital. "We conducted the trials for two different populations, both for adults over 60 years of age -approved last year- and the one intended for pregnant women in the third trimester of pregnancy."
The idea is that the mother generates the antibodies, so that the newborn babies, who are the most at risk population -infants within the first 6 months of life-, are already born with the defenses. If they come into contact with the virus, they can become infected but do not have a severe disease," explained Pérez Marc.
The efficacy of the vaccine up to the third month of life of the babies, according to the clinical trial, was 80 percent, "which means that the protection against severe disease is very good. You can have the disease, but the important thing is that you do not have severe disease", added the expert.
Pérez Marc recalled that bronchiolitis "is the main cause of hospitalization due to respiratory viruses in childhood and kills more than 200,000 children per year in the world. And it most seriously affects children with fewer resources and those who have the greatest difficulty in accessing healthcare, especially in developing countries".
In this sense, the infectologist emphasized that "in a country that has very different populations, depending on the area, many of them with important deficiencies, it is important to have a vaccine like this in the national calendar. The idea is that all pregnant women should have the possibility of having the vaccine".
The step in question is transcendental. Perez Marc explains: "From one year to the next, we are going to have a good amount of antibodies in the blood -we hope this will be the case- in most of the children born in the country".
-What happens if the pregnant woman does not get the vaccine between 32 and 36 weeks?
-It's like a missing vaccine, and in that case the son or daughter who is born is not going to be protected against RSV.
-Can the vaccine no longer be administered at week 37?
-In fact, it is not that it could not be done because it would cause any harm. What happens is that the idea is to apply it between 32 and 36 weeks because after that they are considered full-term children and they can be born. It takes a few days for the mother to generate a good amount of antibodies in her blood and for these to pass to the baby. If the mother is vaccinated at week 37 and the baby is born two days later, he/she will not be protected.
-How long does the vaccine protection last?
-We are still looking at that. The important thing in the study was to have protection when it is most needed. We say in pediatrics that the first month of a baby's life is very important. We tell parents to keep the baby in a "glass capsule" because the immune system is still adapting to the new world and cannot respond well to severe infections. The first three months are also very important: if everything is working well and breastfeeding is established, the baby is starting to establish its own immune system to respond to infections. And obviously the first six months are also important. So this is a vaccine that aims to protect babies in the first three months of life, and it is also extensible to the first six months. That's what we showed in the study: efficacies above 80 percent in the first three months and 60 percent in the first six months. This does not mean that the vaccine cannot continue to protect the population after the first year of life.
-The data on what happens to immunity beyond one year of life could not be confirmed in the study?
-Yes, it comes out of the study, but the neutralizing antibodies in the blood are decreasing. So the vaccine has less and less efficacy. But we also know that since children have a well-developed immune system by the time they are one year old, that is the time when they can, in general, deal with the disease on their own and in a very good way through their immune system.
-Despite the lowering of antibodies, is there cellular immunological memory as with the vaccine or Covid convalescence?
-The memory immune response is generated by the lymphocytes in a cascade of events that cause the immune system alone, even if there are no neutralizing antibodies circulating at that moment, to trigger a memory response because it remembers the infection with which it was in contact at some point, or the vaccine with which it was in contact. This response is very difficult to measure, because it is triggered when the disease appears, but we know from the evolution of the children -and we have also seen it in older adults- that two years after the vaccine has been applied, the efficacy to prevent the disease remains high.
The characteristic of RSV
-Yes, during 2024 and 2025 several vaccines will be investigated. One might ask why we would need a vaccine for children if we see that the vaccine for pregnant women already generates immunity. The answer is that there are a lot of children who will not be born to vaccinated mothers. And there are also mothers who have immunological problems, which prevent them from passing the antibodies to their babies. There are also many cases of higher-risk children who were not responders, and it would be useful to have a pediatric vaccine to give them out there every year. RSV research is going through a revolution, because this is in addition to the research on antivirals for the treatment of the disease once it is triggered.
-In conclusion, if the RSV vaccination campaign is a success, hospitals should certainly be less stressed with bronchiolitis cases this winter.
-That's for sure. It is the first year and we have to do a lot of outreach work and with physicians, which is what we are doing. Surely this year, if the campaign is good, there will be a very important relief and an improvement in the statistics of serious illness due to bronchiolitis. We hope that in the coming years the story will change worldwide.
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