Research indicates that influenza vaccine effectiveness was low but effective in preventing influenza-related hospitalization during the 2016-2017 flu season in Canada.
Active influenza surveillance is needed to help control the spread and severity of epidemic episodes and inform public health decision making pertaining to prevention and treatment efforts. Knowing the burden of the disease and the effectiveness of the influenza vaccine each flu season is crucial for preparing for the next one.
Active surveillance conducted by the Canadian Immunization Research Network Serious Outcomes Surveillance Network for the 2016-2017 flu season found that overall, the effectiveness of the seasonal vaccine was low, but effective in preventing influenza-associated hospitalizations in Canada, according to a new study.
Results of the analysis were presented by Shelly A. McNeil, MD, FIDSA, from the Canadian Center for Vaccinology, IWK Health Centre and Nova Scotia Health Authority, Dalhousie University, Halifax, NS, Canada, in a poster abstract session at the 2018 ID Week Annual Meeting in San Francisco, CA.
For the analysis, McNeil and colleagues conducted active flu surveillance at 13 hospitals throughout 4 provinces from November 5, 2016, to April 30, 2017. Eligibility criteria for enrollment were patients who were admitted to these facilities with any respiratory diagnosis or symptom.
Nasopharyngeal swabs were collected from those included in the analysis and were tested for flu through the use of polymerase chain reaction (PCR). Patients whose tests came back as positive for the virus were considered to be cases, while those whose tests came back negative served as the matched controls.
Investigators pulled patient demographic and medical information from medical records. Flu vaccine effectiveness was estimated as 1- odds ratio (OR) of influenza in vaccinated vs unvaccinated patients x 100% using conditional logistic regression, with corresponding 95% confidence intervals (CI), according to McNeil and colleagues.
Out of the 1431 flu cases that were included in the analysis, influenza A accounted for the majority of infections (n = 1299); all patients with a known influenza A subtype had A/H3N2. Of the 1431 flu cases, 144 (10.1%) were admitted to the intensive care unit and 91 (6.4%) died within 90 days of discharge.
The investigators reported that the overall adjusted flu vaccine effectiveness (VE) for preventing flu-associated hospitalizations in all ages was 23.3% (95% CI: 2.9%-39.4%), with slightly less effectiveness observed in those who were 65 years of age or older (VE: 19.4%; 95% CI: -7.8%-39.8%). Higher vaccine effectiveness was noted in those younger than 65 (VE: 47.9%; 95% CI: 9.9%-69.9%).
As such, McNeil and colleagues concluded that the flu vaccine effectiveness for the 2016-2017 flu season in Canada was low, but effective in preventing flu-associated hospitalizations overall.
Because of the low effectiveness, the investigators stressed that continued assessment of flu vaccine effectiveness is needed to inform immunization policy in Canada and they underscored the need for flu vaccines that will provide stronger protection against the virus.
M. Nichols, None; M. K. Andrew, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. Sanofi Pasteur: Grant Investigator, Research grant; T. F. Hatchette, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. Abbvie: Consultant, Speaker honorarium; A. Ambrose, None; G. Boivin, None; M. Elsherif, None; K. Green, None; J. Johnstone, None; K. Katz, None; J. Leblanc, None; M. Loeb, None; D. Mackinnon-Cameron, None; A. Mccarthy, None; J. McElhaney, GSK: Scientific Advisor, Speaker honorarium. Sanofi Pasteur: Scientific Advisor, Speaker honorarium; A. McGeer, GSK: Grant Investigator, Research grant; Hoffman La Roche: Grant Investigator, Research grant. Sanofi Pasteur: Grant Investigator, Research grant; A. Poirier, Sanofi Pasteur: Investigator, Research grant Actelion: Grant Investigator, Research grant; J. Powis, GSK: Grant Investigator, Research grant. Merck: Grant Investigator, Research grant. Roche: Grant Investigator, Research grant. Synthetic Biologics: Investigator, Grant recipient; D. Richardson, None; M. Semret, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant; D. Smyth, None; S. Trottier, CIHR: Grant Investigator, Research grant; L. Valiquette, None; D. Webster, None; L. Ye, None; S. A. McNeil, GSK: Grant Investigator, Research grant. Pfizer: Grant Investigator, Research grant. Merck: Collaborator and Consultant, Contract clinical trials and Speaker honorarium. Novartis: Collaborator, Contract clinical trials. Sanofi Pasteur: Collaborator, Contract clinical trials.