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TORONTO – This season's influenza vaccine appears to be very effective because it reduces by more than 70% the risk of influenza infection in circulation, much better than what was observed when firing the vaccine. 39 last year, according to Canadian researchers.
Their mid-season badysis, published online Thursday in the journal Euro Surveillance, shows that this year's influenza vaccine is effective in preventing infection with the H1N1 respiratory virus in all age groups .
The discovery is "good news," said Dr. Danuta Skowronski, a senior researcher with the BC Center for Disease Control, saying the effectiveness of last year's vaccination was less than 20%, mainly because of a discrepancy between the vaccine and the H3N2 strain. which prevailed during the 2017-18 season.
Another reason is that the influenza vaccine tends to perform better during H1N1-dominated seasons, she added, noting that Australia had reported comparable efficacy using the same formulation during its recent influenza season.
An effectiveness of about 70% means that vaccination would have prevented seven cases of influenza in unvaccinated people out of ten, had they chosen to be vaccinated, said Skowronski, influenza expert at BCCDC.
"It is therefore a very important risk reduction, especially for people with underlying medical conditions, who face an increased risk of serious complications if they are infected with the flu" she said in Vancouver. "They could have reduced that risk by 70%."
According to the age group, the vaccine efficacy rate for children aged one to eight years was 91%; 71% among 9 to 19 year olds; 68% on average for adults aged 20 to 64; and 65% among those aged 65 and over.
With H1N1 influenza being dominant, young children were particularly affected by the flu this year, probably because they had never been exposed to this viral strain, if any, and therefore did not acquire any natural immunity. The last three H1N1 outbreaks occurred in 2015-16, 2013-14, and 2009, while some of today's children would not be born.
As of January 12, more than 600 children aged 16 and under had been hospitalized, of whom 93 were in intensive care and at least seven – all under the age of 10 – died of the flu, says the officer. Public Health Agency of Canada (PHAC). The death of a three-year-old Quebec girl last week would not have been taken into account in this report.
Skowronski said children were disproportionately affected by the flu this year. Children under nine accounted for 28% of the 661 cases badyzed for vaccine effectiveness, even though they only account for about 10% of the country's population.
"That's why I think we're seeing more young people this year being included in hospitalization calculations for H1N1," she said. "It's not that the virus is more virulent, we have higher rates of attack in young children.
"When you have more infected people, more attack rates and the same proportion of serious casualties, the absolute number of serious consequences will be higher."
PHAC reported on its FluWatch weekly website that, as of January 12, 20,494 laboratory-confirmed influenza cases had been reported by the provinces and territories, most of them due to H1N1 and mostly to the less 65 years old.
More than 1,500 resulted in hospitalization, including 227 ICU admissions and 47 deaths.
PHAC only collects data on laboratory-confirmed cases of people who have been tested after consulting a physician. The actual number of Canadians who contracted the flu without consulting a health care provider would be many times higher.
Vaccine efficacy badysis was conducted by researchers at the Canadian Sentinel Practitioners Monitoring Network, headquartered at BCCDC. The network includes hundreds of primary care practitioners in British Columbia, Alberta, Ontario and Quebec, who collect positive test results for influenza and vaccine status of outpatients. People treated at the hospital are not included in the data.
Skowronski said that there was a lot of regional variation in the timing and intensity of the flu epidemic in the country. Alberta and British Columbia, for example, began seeing cases early in the season, while eastern parts of Canada were affected later and may have not be reached to their maximum.
"We have pbaded the summit here and we are downhill," she said of British Columbia. "But even on the slopes of the epidemic curve, there will be activity for several weeks."
It is not too late for unvaccinated people to get vaccinated, especially in areas of the country where the number of cases is increasing, Skowronski advised.
"That's why it was important for us to get this estimate (vaccine efficacy) because it provides substantial protection, which can still be important in high-activity areas.
"And do not forget that influenza B has not done much in the show this year, and that it usually appears later in the season."
Last season, only 38% of Canadian adults were vaccinated against influenza, and vaccine adoption varied with age and risk factors for complications, said a PHAC spokesperson.
– Follow @SherylUbelacker on Twitter.
Sheryl Ubelacker, Canadian Press
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