Annual vaccination has proven to be an effective method to reduce the burden of influenza disease [3]. In Germany, vaccination against seasonal influenza is recommended by the Standing Committee on Vaccination (STIKO) for individuals who have either an increased risk to develop severe influenza disease (i.e. persons aged ≥60 years, pregnant women, and persons with certain chronic medical conditions) or who are likely to transmit the virus to vulnerable groups (e.g. health care workers (HCW)) [4]. Vaccination is free of charge for the target groups in Germany. During the influenza pandemic 2009/10, STIKO additionally recommended vaccination with a monovalent vaccine against the pandemic influenza virus strain A(H1N1)pdm09 for the whole population. Due to expected limitations in vaccine supplies at the beginning of the vaccination campaign, STIKO defined and ranked priority groups for the pandemic vaccination: 1) HCW, 2) persons with underlying chronic conditions, 3) pregnant women, 4) household contacts of vulnerable persons, 5) all other persons aged 6 months to 24 years, 6) all other persons aged 25–59 years, 7) all other person aged 60 years and above [5]. The pandemic vaccination campaign started in Germany on 26 October 2009 [6]. The AS03-adjuvanted monovalent vaccine Pandemrix® was almost exclusively used and available in sufficient quantities [7].

During the pandemic, vaccination against A(H1N1)pdm09 was subject to controversial discussions, not only in Germany but also in many other countries worldwide [7-9]. Main topics of the debate in the media and among experts and ‘self-proclaimed experts’ were vaccine safety, effectiveness, and concern that there were too little data on the new vaccines or vaccine ingredients (especially new adjuvants) available. Moreover, the general necessity of vaccination in view of the relative mildness of the pandemic influenza disease was called into question [7,9-11]. As a result, compliance with the national recommendations for pandemic vaccination was very poor in Germany. Since Germany has no central immunization registry, information on vaccination coverage (and factors influencing coverage) is only available from telephone and household surveys [12-15]. According to the results of thirteen consecutive cross-sectional telephone surveys (total n=13,010) conducted during the pandemic, only 8.1% of the general population aged ≥14 years living in Germany received a vaccine against pandemic influenza [6].

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 [6] 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 [23], France [24], Australia [25], and the US [26]) 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 ​Figure2,2, 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%) [29]. 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 [30]. 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 [29]; US: 41.2% among all persons aged ≥6 month [31]). 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 [27] vs. 71.0% in season 2010/11 [32]). 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 [33]. Conversely, believing that the pandemic vaccine is safe was significantly associated with the receipt of the pandemic vaccine in many countries worldwide [21]. 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 [34]. 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.