Estimating pandemic vaccine effectiveness in two Italian regions using the screening method, 2009-2010

The objective of this study, conducted within the I-MOVE project, was to estimate pandemic VE against laboratory confirmed cases in two Italian regions using the screening method. We calculated vaccine coverage using the number of first doses of pandemic vaccine administered and demographic data. A case was defined as a patient who was swabbed from week 44 of 2009 to week 3 of 2010 and who tested positive for A/H1N1v using RT-PCR. A case was considered vaccinated against influenza A/H1N1v if she/he had received one dose of the vaccine more than 14 days before swabbing. We used Farrington's method to build the confidence intervals. We included in the analysis 755 confirmed A/H1N1v cases. The median age of cases was 24 years (range 0-89). One case (0.1%) had received one dose of vaccine more than 14 days after swabbing. The overall crude estimated VE was 92.4% (95% CI: 46.3-98.9). It suggests that the pandemic vaccine offered good protection against medically attended laboratory-confirmed A/H1N1v.