Number needed to vaccinate to prevent hospitalizations of pregnant women due to inter-pandemic influenza in Sweden, 2003-2009

Because of the increased risk associated with influenza A(H1N1)pdm09, vaccination is presently offered to all pregnant women in Sweden, but vaccination against other inter-pandemic influenza types seems disputable. The study illustrates the context dependence of preventive health measures and points to the need for national NNV estimates and international harmonization of study methods for comparisons between countries.