Influenza vaccine averted illnesses in Chile, Guyana, and Paraguay during 2013–2018: a standardized approach to assess value of vaccination

Abstract

Background To better establish the value of vaccination against influenza viruses, we estimated vaccine-averted influenza illnesses among young children and older adults in Chile, Guyana, and Paraguay. Methods We gathered country- and target population-specific data on monthly influenza hospitalizations, vaccine coverage, and vaccine effectiveness from surveillance records and immunization registries during 2013-2018. We applied a static compartmental model to estimate differences in the number influenza-associated respiratory disease events (symptomatic non-hospitalized illnesses, medically attended illnesses, hospitalizations) in the presence and absence of influenza vaccination programs. Results Between 2013 and 2018, vaccinating 68% of children aged 6–23 months in Chile averted an annual mean of 14,617 non-hospitalized, 9,426 medically attended, and 328 hospitalized influenza illnesses; vaccinating 28% of children aged 6–23 months in Paraguay averted 1,115 non-hospitalized, 719 medically attended, and 25 hospitalized influenza illnesses. Vaccinating 59% of older adults in Chile averted an annual mean of 83,429 non-hospitalized, 37,079 medically attended, and 1,390 hospitalized influenza illnesses; vaccinating 36% of older adults in Paraguay averted an annual mean of 3,932 non-hospitalized, 1,748 medically attended, and 66 hospitalized influenza illnesses. In Guyana, a hypothetical campaign vaccinating 30% of children <5 years could have prevented an annual 1,496 non-hospitalized, 971 medically attended, and 10 hospitalized influenza illnesses. Vaccinating 30% of adults ≥65 years could have prevented 568 non-hospitalized, 257 medically attended, and 10 hospitalized influenza illnesses. Conclusions Influenza vaccination averted tens of thousands of illnesses and thousands of hospitalizations in Chile and Paraguay; influenza vaccination could have had a proportional benefit in Guyana.