Underreported influenza mortality in Central and Eastern Europe hinders the extension of seasonal influenza vaccination programs in older adults

Several Central and Eastern European (CEE) countries have low seasonal influenza vaccination coverage of older adults coupled with severe underreporting of influenza-related deaths. Our objective was to project influenza mortality estimates for older adults in six CEE countries, building on high-quality mortality data from an EU-15 country with similar climate, population density, and seasonal influenza vaccination coverage. In addition, we aimed to compare the implications of the reported and projected influenza burden estimates on the economic value of extended influenza vaccination for older adults in an exemplary CEE country, Serbia. Multivariate regression modelling was used to adjust for differences in population health status between countries. Economic implication of underreporting influenza burden was investigated by using the VITALO decision analytic model. Locally reported and projected mortality rates were similar in Czech Republic and Slovenia, whereas projected mortality rates far exceeded locally reported influenza mortality rates in Poland, Hungary, Serbia, and Romania. Based on locally reported mortality rates in Serbia, increasing seasonal influenza vaccination coverage in the 65+ population to average coverage in the EU-27 would prevent 2.86 deaths and would generate 16.52 QALYs at the incremental cost of 2,847,994 EUR annually, which translates to 172,378 EUR/QALY incremental cost-effectiveness ratio (ICER). However, adopting Austrian influenza mortality rates adjusted to higher frailty prevalence in Serbia, increased vaccination coverage would prevent 28.96 deaths and generate 132.77 QALYs at the incremental cost of 2,803,675 EUR annually with an 21,116 EUR/QALY ICER, below Serbian willingness to pay threshold. Accordingly, extension of seasonal influenza vaccination in older adults would be a cost-effective public health intervention in Serbia. Underreporting of adult influenza mortality rates prevent policymakers from understanding the true economic value of influenza vaccination. Our approach is applicable in further countries with low reported influenza mortality rates.