The aim of this study was to assess the uptake of seasonal influenza vaccines in specific target groups for seasons 2008/09 and 2009/10, as well as for pandemic influenza vaccines during the pandemic season 2009/10 in Germany in the total adult population by using data from a large population-representative telephone survey. By using data from a smaller follow-up survey, our study moreover provides the only so far available data on seasonal influenza vaccination coverage in Germany for the post-pandemic season 2010/11. Overall, only 8.8% of the adult population in Germany followed the official recommendation and received a vaccination against pandemic influenza in season 2009/10. The follow-up survey revealed a decrease in seasonal influenza vaccine uptake in the first post-pandemic season across all target groups when compared to the pre-pandemic season 2008/09, most prominent among HCW. With an average coverage of 50% in the elderly, 41% in the chronically ill, and 28% in HCW in seasons 2008/09 to 2010/11, the EU goal of reaching a seasonal influenza vaccination coverage of at least 75% in the target groups  has not yet been achieved in Germany.
Having received a seasonal influenza shot in the pre-pandemic season was the strongest predictor for receiving pandemic influenza vaccination in our study. The high correlation between seasonal and pandemic influenza vaccine uptake highlights the significance of habitual behaviour with regard to influenza vaccination decisions. In addition and independent from this factor, persons belonging to at least one of the recommended target groups for seasonal influenza vaccination were significantly more likely to receive a pandemic influenza vaccination than persons not belonging to a target group. Our results are broadly in line with the findings of a prospective monitoring survey on pandemic influenza vaccination in Germany  and two reviews investigating determinants of pandemic vaccine uptake [21, 22]. Prior seasonal vaccination was not only found to be positively associated with the intention to receive the pandemic vaccination among adults in several industrialized countries (e.g. in the UK , France , Australia , and the US ) but also with the actual receipt of the vaccination (e.g. [6, 27, 28]). When developing vaccination strategies for future pandemic situations one should therefore consider targeted strategies for enhancing coverage among those who do not fall within the target groups for seasonal influenza vaccination and thus do not regularly receive a seasonal influenza shot. A further opportunity to enhance compliance with national recommendations and therefore vaccination coverage in a future pandemic situation could be to increase seasonal vaccine uptake in the target groups. However, major reasons for not being vaccinated were the perception that vaccination was not necessary or not safe. It can be assumed that both reasons will not be barriers to high pandemic vaccine uptake in a future pandemic setting if the mortality is much higher than during the 2009/10 pandemic.
A higher uptake of seasonal influenza vaccines in season 2009/10 was observed in the follow-up survey population when compared to the total GEDA10 study population in 2009/10. It is therefore very likely that the point estimates for seasonal influenza vaccination coverage for the 2010/11 season, which were based on data from the same follow-up survey, were also overestimated. Taking into consideration that acceptance of seasonal influenza vaccination was higher in the follow-up survey population, our study results suggest that seasonal influenza vaccine uptake in the recommended target groups in Germany has decreased in the post-pandemic season 2010/11, not only in comparison to season 2008/09 but also to the pandemic season 2009/10 (compare Figure 2, empty symbols). Hence, our findings are discordant with observations made in several other industrialised countries. For instance, seasonal influenza vaccination coverage in the UK remained stable between seasons 2009/10 and 2010/11 among at risk persons under 65 years of age (51.6% vs. 50.4% vaccination coverage) as well as among persons aged ≥65 years (72.4% vs. 72.8%) . Among high-risk persons aged 18–64 years living in the US, seasonal influenza vaccine uptake was 46.2% in the pandemic and 46.7% in the post-pandemic season . However, in both countries acceptance and uptake of pandemic influenza vaccination was higher as compared to Germany (UK: 37.6% vaccination coverage in clinical risk groups ; US: 41.2% among all persons aged ≥6 month ). In France, despite the poor uptake of pandemic influenza vaccines (11.1%), an increase in seasonal influenza vaccine uptake was observed in the post-pandemic season among persons aged ≥65 years with underlying chronic conditions (62.6% in season 2009/10  vs. 71.0% in season 2010/11 ). In the upcoming years, the uptake of seasonal influenza vaccines should be carefully monitored in Germany in all target groups to identify if this trend continues. Especially the strong decrease in vaccination coverage among HCW is of concern, and communication activities should be strengthened especially for this target group not only to achieve individual protection of this target group but also to protect vulnerable patients managed by HCW.
In our study ‘fear of side effects’ was found to be the most frequently stated reason for rejecting pandemic vaccination, thereby confirming findings of 13 smaller consecutive surveys carried out during the pandemic in Germany . Conversely, believing that the pandemic vaccine is safe was significantly associated with the receipt of the pandemic vaccine in many countries worldwide . Appropriate addressing of vaccine safety concerns by public health authorities may be an important factor to maintain public trust in national vaccination recommendations and beyond that to enhance vaccine uptake in future pandemic situations [22, 33].
In our study, 8.5% of those who did not receive a pandemic influenza vaccination stated that they reject vaccinations in general. This translates into a proportion of 7.7% for the total study population. Little is known about the exact proportion of vaccination opponents among the general adult population in Germany. In a recent survey performed by the German Federal Centre for Health Education (BZgA) among 3,002 parents of children aged 0–13 years, 35% stated that they reject particular vaccinations for their children, but only 1% of parents reject vaccinations in general . Since our study did not focus on the general rejection of vaccinations in the population, we did not ask further detailed questions related to this topic to verify this attitude and the underlying reasons. Therefore, this figure must be interpreted with caution.
Our study has some limitations that need to be acknowledged. Calculation of influenza vaccination coverage was based on self-reported vaccination status and may therefore be prone to recall problems. However, it was shown in several studies that self-report of influenza vaccination status has an adequate degree of validity [35, 36]. Furthermore, the response rate in GEDA10 was comparatively low at 29%. However, it should be noted that the chosen method of calculating the response rate (namely Response Rate 3 as defined by AAPOR ) is a very conservative approach and that our response rate is comparable to studies using the same approach (e.g. CDC-Behavioral Risk Factor Surveillance Rates Report ). Finally, it cannot be ruled out that other reasons than the controversial discussions on the pandemic vaccination have also contributed to the observed drop in seasonal influenza vaccination coverage in 2010/11.