A Canadian program led by BC Centre for Disease Control (BCCDC) scientists published the first estimates of vaccine effectiveness for this year’s flu vaccine, showing it is reducing the risk of respiratory illness due to influenza and requiring a medical visit by about half.
The results published January 30 in
Eurosurveillance come from the Canadian Sentinel Practitioner Surveillance Network (SPSN), which is headquartered at the BCCDC, and involves four of Canada's largest provinces: Alberta, British Columbia, Ontario and Quebec as well as the National Microbiology Laboratory.
“We found that for vaccinated people, the risk of having influenza illness severe enough to require a doctor’s visit is cut in half compared to unvaccinated people," says Dr. Danuta Skowronski, lead of the SPSN and a physician with the BCCDC's Immunization Programs and Vaccine Preventable Diseases Service. “That’s quite a substantial reduction in risk provided by the influenza vaccine this season.”
Influenza A has been the most frequently reported influenza type in Canada since the start of this year’s respiratory season. There are two types of influenza A circulating: A(H1N1) and A(H3N2). Among SPSN participants, there has been mostly A(H1N1), with lower A(H3N2) co-circulation so far.
Vaccine effectiveness estimates by the SPSN are based on specimens and data collected from patients seeking medical care for acute respiratory illness at a community clinic or primary care provider that is registered with the sentinel network. The SPSN team found that vaccine cut the risk of medically attended influenza illness by about half compared to unvaccinated people, similar for both subtypes at 53 per cent for A(H1N1) and 54 per cent for A(H3N2).
"We are in the middle of respiratory season with influenza activity still peaking," says Dr. Skowronski. “For most people influenza is a nasty infection that can lead to missed work or school. When influenza is circulating in our communities, it also leads to increase in medical visits. For some people, it can cause even more severe outcomes like hospitalization and death.”
To better understand the match between the vaccine and circulating strains of influenza, the team applied whole genome sequencing to about one in three influenza viruses they detected. The influenza virus is known to be highly changeable, meaning it mutates to avoid immunity. Investigators found that about 80 per cent of sequenced A(H1N1) viruses belonged to a different genetic clade than the current season’s vaccine. Virtually all A(H3N2) viruses belonged to the same genetic clade as the vaccine but with some mutations that SPSN investigators have flagged as warranting further monitoring. The SPSN will be submitting its genetic and vaccine effectiveness findings to the World Health Organization alongside the Global Influenza Vaccine Effectiveness (GIVE) network to help inform the need for vaccine strain update.
- Get immunized – this is the best way to prevent serious illness
- Stay at home if you’re feeling sick
- If you have any symptoms of respiratory illness and must leave your home, practice respiratory etiquette:
- Wear a mask in indoor public spaces
- Cough and sneeze into your elbow
- Clean your hands regularly
- Avoid touching your face, especially your eyes, mouth and nose
- If you’re sick, stay away from people at higher risk of serious illness
- If seeking care for flu-like illness, notify your provider or clinic upfront and wear a mask to prevent spreading infection to other patients or staff in the area
