Estimating the number of averted illnesses and deaths as a result of vaccination against an influenza pandemic in nine low- and middle-income countries.

Background: During the 2009 influenza A(H1N1)pdm09 pandemic, 77 countries received donated monovalent A(H1N1)pdm09 vaccine through the WHO Pandemic Influenza A(H1N1) Vaccine Deployment Initiative. However, 47% did not receive their first shipment until after the first wave of virus circulation, and 8% did not receive their first shipment until after the WHO declared the end of the pandemic. Arguably, these shipments were too late into the pandemic to have a substantial effect on virus transmission or disease burden during the first waves of the pandemic.

Objectives: In order to evaluate the potential benefits of earlier vaccine availability, we estimated the number of illnesses and deaths that could be averted during a 2009-like influenza pandemic under five different vaccine-availability timing scenarios.

Methods: We adapted a model originally developed to estimate annual influenza morbidity and mortality burden averted through US seasonal vaccination and ran it for five vaccine availability timing scenarios in nine low- and middle-income countries that received donated vaccine.

Results: Among nine study countries, we estimated that the number of averted cases was 61-216,197 for actual vaccine receipt, increasing to 2,914-283,916 had vaccine been available simultaneously with the United States.

Conclusions: Earlier delivery of vaccines can reduce influenza case counts during a simulated 2009-like pandemic in some low- and middle-income countries. For others, increasing the number of cases and deaths prevented through vaccination may be dependent on factors other than timely initiation of vaccine administration, such as distribution and administration capacity.