Childhood bronchiolitis returns, the virus overshadowed by covid

Santa Coloma de GramenetThe paediatric emergencies re-live a winter in the middle of June. The respiratory syncytial virus (RSV), the cause of bronchiolitis, has returned to consultation and intensive care units (ICU) after months of forced disappearance by the pandemic. This time, moreover, it is breaking the patterns of pediatricians: until now it was a virus with a very seasonal behavior and related to the cold. There have always been big peaks of bronchiolitis between the months of November and March. However this year, there have been less than half the expected number of cases. On the other hand, from April onwards - already outside the usual calendar for this virus and with covid increasingly under control - both the number of cases and hospitalisations have risen. In general clinics, for example, the week of May 17, there were more than 200 cases in children under five years old, a figure not seen since February 2020.

RSV spreads in the off-season. "It's a virus that causes an annual epidemic and it's very common for children to get it in the winter. What is exceptional, and I had not seen in thirty years of profession, is that the outbreak did not exist in winter and appeared in the spring, at the gates of summer", explains the head of the pediatric service of the Hospital Sant Joan de Déu, Juanjo Garcia. In this reference center for the child population, between October and March only one child was admitted for bronchiolitis. Now, and since mid-May, they attend to 30 a week and there are a few who remain hospitalized. "We do not reach the levels of a normal winter, but these are many for the summer season", says Garcia.

In the Vall d'Hebron there are also about fifteen children admitted with inflamed bronchioles, twice as many as fifteen days ago. At this time a year ago, in the middle of covid, there were none, or almost none, according to the head of pediatric infectious diseases of the center, Pere Soler. "In February we were already beginning to receive some cases of bronchiolitis. While we are far from a peak of 40 or 50 admissions as happened other years, the rise is continuous", he explains. He assures us that the last few weeks of the hospital's on-calls are more similar to those of October and November than to those of June, and says that "this has never happened before".

In the coldest months of the year, bronchiolitis is the cause of more than half of the pediatric emergencies in the country. Although they can also get sick, children over the age of one year do not usually suffer major complications: as they get older, the symptoms increasingly resemble the common cold. For parents of infants, however, bronchiolitis is a nightmare. "It can cause them to have severe breathing difficulties and be admitted to the hospital, some to the ICU", says Garcia. For pediatricians, RSV outbreaks are also one of the most complex episodes to manage. "Unlike covid, bronchiolitis in pediatric patients is of particular concern to us: the consequences can be very serious if the child enters an ICU, the emergency room can become overwhelmed and families go through a trance", says Soler.

Masks and restrictions

Last year, however, the coronavirus eclipsed the other viruses that spread through the respiratory tract and cases of bronchiolitis plummeted. They virtually disappeared from major hospitals, compared to the volume of care in the year before covid. "2020 was the best year for children's health: all respiratory viruses and pneumonia caused by bacterial diseases were reduced to a minimum", explains Garcia. This winter only two cases of bronchiolitis were treated when, in a usual winter, they received between 1,300 and 1,500 cases.

This trend has been reproduced in several countries around the world and the specific causes are unknown, but experts attribute this shift in seasonal circulation patterns of respiratory viruses to individual and collective protection measures: the use of masks, increased hand washing especially in schools, social distancing and mobility restrictions.

Immunity to RSV is partial, as with influenza, and reinfection is possible from season to season. The absence of bronchiolitis for a whole year, however, also means that there is now a large volume of children who have not had contact with the virus and are therefore susceptible to infection in the same period of time. "Now we will have to see if the de-escalation [of covid] increases the number of cases or if the fact that the end of school truncates this circulation", summarizes Soler.

"I don't think there will be an avalanche of sick people. The most logical thing would be that, with the heat and the end of school, the curve stays a few weeks at the same level and then goes down", says Juanjo Garcia. However, the pediatrician admits that there is much uncertainty about the pattern of behavior of respiratory viruses from now on. "It may be that they lose their seasonality until the pandemic situation is straightened a bit, since covid will remain more as a virus. This does not necessarily mean that the severity of RSV cases will increase, but everything indicates that we will go at the wrong time, as we are seeing now", he concludes.

Looking to other countries

The article Uncertain effects of the pandemic on respiratory viruses, published in the journal Science, also notes that as restrictions are relaxed and covid vaccination programmes increase, countries are beginning to report increased activity and circulation of certain epidemic viruses. "What can we expect once the pandemic subsides and containment measures are lifted? If there is reduced immunity [to RSV] in the population, endemic respiratory viruses may re-emerge in atypical patterns or with elevated attack rates (increased risk of infection during a specific time period) due to the large susceptible population", the study states.

Pediatricians consulted by ARA admit that the behavior of RSV in southern hemisphere countries, such as Australia, can be a warning for the rest of the world, especially in Europe. "Australia controlled the covid relatively easily, but when they took off their masks and the population relaxed, which it did quite quickly, they were the first to have a very important peak of bronchiolitis", says Soler, a pediatrician at Vall d'Hebron.

On the other hand, experts also note that in many Latin American countries covid has exerted a "niche effect", since they have high rates of coronavirus and little of RSV, while in France, for example, weeks ago the two viruses circulate at the same time. "Possibly because there they are more relaxed in about compliance with the restrictions," adds Soler.

And what about Catalonia? According to the pediatrician, as there is less circulation of covid, and although not all measures have been withdrawn, the relaxation has opened the door to other respiratory viruses. At the state level, in fact, where we are seeing an increase in these cases is in the two most densely populated areas and with more social interaction: Barcelona and Madrid, with its metropolitan areas.