The number needed to vaccinate (NNV) and population extensions of the NNV: Comparison of influenza and pneumococcal vaccine programmes for people aged 65 years and over

The number needed to treat (NNT) and population extensions of the NNT describe the population outcomes of disease treatment, usually for chronic diseases. We have developed similar measures for vaccine preventable diseases based on the number needed to vaccinate. These measures quantify the number of people, or the number of vaccine doses, needed to prevent one event due to disease per year and allow the calculation of the vaccine cost to prevent one event due to disease per year. We used this method to compare influenza and pneumococcal vaccine programmes for people aged 65 years or more. We calculated the vaccine cost ($AUD) to prevent a case of disease, a hospitalisation or a death due to influenza or invasive pneumococcal disease each year in this age group. For influenza, the vaccine costs were $598 to prevent one case per year, $10,787 per hospitalisation prevented and $74,801 per death prevented each year. We assumed all cases of invasive pneumococcal disease were hospitalised so the vaccine cost of $11,494 per case prevented was the same as the vaccine cost per hospitalisation prevented, while the vaccine cost per death prevented each year was $49,972. These results suggest the vaccine costs for the prevention of one hospitalisation or one death each year due to invasive pneumococcal disease among the elderly in Australia would be similar to the costs for the prevention of one hospitalisation or death due to influenza. © 2004 Elsevier Ltd. All rights reserved.