The flu hit children under 10 this year, a result that is significantly different from previous years, says Dr. Quebec and researcher Gaston De Serres.
Puppies aged 0 to 9 – unvaccinated – accounted for 29% of all influenza cases in 2018-19 season. This age group represents less than 10% of the population.
And the 2009 H1N1 pandemic is not foreign to the situation, he says.
With colleagues, including some of the Quebec National Institute of Public Health (INSPQ), he used data from the Canadian network Sentinel Practitioner Surveillance Network, which is designed to be measured annually.
They looked at anyone who saw a doctor for flu-like symptoms, including fever, cough, and at least one other symptom. Samples were taken and then it was possible to find out who caught the flu.
The data covers the period from 1 November 2018 to 18 March 2019 in four provinces: Quebec, Ontario, Alberta and British Columbia.
Surprisingly, they found that 29% of the entire population infected during this period were under 10 years of age. While in 2016-17 there were only 17% in this age group 0-9 years and 12% in 2013–2014.
"This share is really bigger this year than in previous years," says Gaston De Serres, a medical epidemiologist and professor at the Medical School and researcher at the Quebec University Hospital – Laval University and INSPQ.
"We tried to understand this and one of the key elements is that children under the age of 10 are children born from a pandemic of 2009, a H1N1 pandemic," he explained. ,
That year, the H1N1 virus affected a large number of children, and those who were infected benefited from some immunity to the virus, he says. He quotes studies that found that in 2009, as many as 50-60% of children were infected.
"With such a large share, the virus has trouble moving around in this group afterwards." "
One of the data in this analysis supports this conclusion: relatively few cases of influenza have been reported in people aged 10 to 19, those who were young children in the 2009 pandemic. in 2018–2019 it was only 7% of cases.
But those who were born after 2009, children from 0 to 9 years, did not use this protection.
Another hypothesis put forward for this 29% result is that half of the current cohort under 10 now attends school, a situation that promotes the spread of the virus.
"At the level of communicable diseases, one of the factors that will speed up transmission is the number of contacts between them. The more we are in contact, the more likely we are to catch the disease or hand it over, ”says the researcher.
According to him, the vaccine was relatively effective this year, up to 70% protection against H1N1.
The research results were published in a scientific journal Eurosurveillance,