Background. Despite the known relatively high disease burden of influenza, data are lacking regarding a critical epidemiological indicator, the case-fatality ratio. Our objective was to infer age-group and influenza (sub)type specific values by combining modelled estimates of symptomatic incidence and influenza-attributable mortality. Methods. The setting was the Netherlands, 2011/12 through 2019/20 seasons. Sentinel surveillance data from general practitioners and laboratory testing were synthesised to supply age-group specific estimates of incidence of symptomatic infection, and ecological additive modelling was used to estimated influenza-attributable deaths. These were combined in an Bayesian inferential framework to estimate case-fatality ratios for influenza A(H3N2), A(H1N1)pdm09 and influenza B, per 5-year age-group. Results. Case-fatality estimates were highest for influenza A(H3N2) followed by influenza B and then A(H1N1)pdm09, and were highest for the 85+ years age-group, at 4.76% (95% credible interval (CrI): 4.52-5.01%) for A(H3N2), followed by influenza B at 4.08% (95% CrI: 3.77-4.39%) and A(H1N1)pdm09 at 2.51% (95% CrI: 2.09-2.94%). For 55-59 through 85+ years, the case-fatality risk was estimated to double with every 3.7 years of age. Conclusions. These estimated case-fatality ratios, per influenza sub(type) and per age-group, constitute valuable information for public health decision-making, for assessing the retrospective and prospective value of preventative interventions such as vaccination, and for health economic evaluations.

Background Claims of influenza vaccination increasing COVID-19 risk are circulating. Within the I-MOVE-COVID-19 primary care multicentre study, we measured the association between 2019–20 influenza vaccination and COVID-19. Methods We conducted a multicentre test-negative case-control study at primary care level, in study sites in five European countries, from March–August 2020. Patients presenting with acute respiratory infection were swabbed, with demographic, 2019–20 influenza vaccination and clinical information documented. Using logistic regression we measured the adjusted odds ratio (aOR), adjusting for study site and age, sex, calendar time, presence of chronic conditions. The main analysis included patients swabbed ≤7 days after onset from the three countries with <15% of missing influenza vaccination. In secondary analyses, we included five countries, using multiple imputation with chained equations to account for missing data. Results We included 257 COVID-19 cases and 1631 controls in the main analysis (three countries). The overall aOR between influenza vaccination and COVID-19 was 0.93 (95% CI: 0.66–1.32). The aOR was 0.92 (95% CI: 0.58–1.46) and 0.92 (95%CI: 0.51–1.67) among those aged 20–59 and ≥60 years, respectively. In secondary analyses, we included 6457 cases and 69272 controls. The imputed aOR was 0.87 (95% CI: 0.79–0.95) among all ages and any delay between swab and symptom onset. Conclusions There was no evidence that COVID-19 cases were more likely to be vaccinated against influenza than controls. Influenza vaccination should be encouraged among target groups for vaccination. I-MOVE-COVID-19 will continue documenting influenza vaccination status in 2020-21, in order to learn about effects of recent influenza vaccination.