Everyone remembers that last November an influx of infants suffering from acute bronchiolitis, up to 8,500 per week, of which a third required hospitalization, caused very great strain on hospital pediatric services and in particular the units intensive care. Some children from Ile-de-France even had to be transferred to other regions. This crisis situation has revealed the difficulties of the pediatric hospital service, which are the subject of extensive reflection at the present time. But beyond these structural problems, advances in medicine could, in the future, prevent or in any case greatly limit the scale of these winter epidemics.
Acute bronchiolitis is a lung infection to which young infants, especially premature infants, and the elderly, including those with cardiopulmonary conditions, are particularly vulnerable. The most common cause of infection is the highly transmissible respiratory syncytial virus (RSV). It occurs in the form of seasonal epidemics in late autumn. It is estimated that 30% of infants are affected each year, with 5 to 10% of them developing an infection requiring hospitalization. In addition, in the United States, the number of cases in the elderly is estimated at 100,000 per year, of which 5 to 10% die. To date, there is no really effective curative treatment against this virus.
Advances in prevention occurred about a quarter of a century ago through the use of passive immunotherapy. This is the injection once a month to infants at risk (very premature babies in the first place) of a monoclonal antibody directed against RSV, which reduces the risk of infection. Last year, a new antibody with a long-lasting protective effect became available that protects up to 75% of treated infants. This is an undeniable advance, but still reserved for a small fraction of children.
The hope of vaccines
For more than sixty years, scientists have sought to develop a vaccine against RSV. Until recently, all these attempts have failed. The occurrence of some adverse effects, and in particular a worsening of the infection, caused by a vaccine composed of inactivated virus led to progress with the greatest caution. Ten years ago, a breakthrough was the formulation of a vaccine based on the virus’s fusion protein (F), which allows it to infect cells of the respiratory tract. Injection of a stabilized form of the protein in its “prefusion” configuration generates protective neutralizing antibodies.
Based on this principle, several vaccines have been developed, relying on different technologies (protein vaccine supplemented with an adjuvant, adenoviral vector or even messenger RNA). The results of various large randomized clinical trials have recently been published. In the elderly, the injection of the first two types of vaccines reduces the risk of a serious form of the infection by 80% to 90% with satisfactory tolerance. The first of them has just obtained marketing authorization in the United States. Europe is very likely to follow soon. A clinical trial of vaccination of pregnant women between 24 and 36 weeks of pregnancy with a protein vaccine reduces the risk of occurrence of severe forms of bronchiolitis in their children by 82% in the first three months of life and by 69% at six months. Here again, the tolerance of the vaccine appears to be good.
These results are very encouraging, they lead us to consider with all the necessary caution (which implies confirmation of the results of the vaccination of pregnant women) the proposal to vaccinate the elderly, on the one hand, pregnant women, on the other hand, to protect their babies. In the latter case, a special educational effort will have to be made to convince pregnant women, some of whom still too often remain resistant to recommended vaccines such as influenza or SARS-CoV-2. The fact that a variety of vaccine technologies will probably soon be available is also a step in the right direction. As noted in a recent editorial in New England Journal of Medicine, we may be living “the beginning of the end” of RSV bronchiolitis epidemics.
* Alain Fischer is President of the Academy of Sciences and co-founder of the Institute of Genetic Diseases