Background
Life expectancy has increased around the world, resulting in a larger proportion of older people in the population. It is estimated that by 2060, 28.4% of the population in the EU will consist of people older than 65 years of age, which would be an increase of almost 10% since 2014 [
1]. Age-dependent deterioration of the immune system, called immunosenescence, together with general frailty and possible co-morbidity make older people particularly susceptible to infectious diseases [
2,
3]. Infectious diseases play an important role in the disease burden of older people and an increased social engagement among community-dwelling older adults might additionally increase the risks of transmission [
4‐
6]. Moreover, immunity – vaccine and naturally acquired – can wane over time which makes reactivation of certain latent viruses possible [
7]. Successful (re)vaccination of older people against vaccine preventable diseases (VPDs) may be an important preventive strategy for reducing the disease burden and health care costs in the aging population. Vaccines against influenza, pneumococcal disease, herpes zoster and pertussis are available, but only influenza is routinely offered to people aged 60 years and older in the Netherlands [
8]. The diseases occur frequently among older people in the Netherlands [
9] and vaccination against pneumococcal disease and herpes zoster is amongst others routinely offered to people aged 65 and 70 years of age respectively in the UK, while vaccination against pertussis is amongst others offered to people aged 65 in Belgium [
10]. These vaccines are currently also being evaluated by the Dutch Health Council on their suitability to be routinely offered to older people in the near future.
As is the case in many European countries, general practitioners (GPs) carry out the national influenza vaccination program by selecting and inviting eligible patients from their registries and administering vaccination in the Netherlands. Moreover, previous research showed that the advice of the GP to get vaccinated was mentioned as the most important external influence on acceptance of vaccination by older people [
11]. For this reason, they are the most likely choice in the Netherlands to administer vaccination when implementing new vaccination strategies for older people and to offer vaccination against infectious diseases other than influenza vaccination to elderly populations. Consequently, the feasibility of expanding the current program also depends on the willingness of GPs to organize and endorse new vaccination strategies. However, little is known about Dutch GPs’ attitude towards expanding the program for elderly people with additional vaccines, whether they would be willing to offer and administer those vaccines and under which circumstances.
Recently, a qualitative study was conducted in the Netherlands [
12] exploring the attitude of GPs towards vaccinating older people and towards adding pneumococcal, herpes zoster and pertussis vaccination to the current program. In an effort to quantify the findings of this qualitative study, we conducted a cross-sectional study investigating the relative and combined strength of the identified factors and underlying beliefs in explaining the intention of GPs to vaccinate people aged 60 years and older against more infectious diseases than influenza.
Discussion
This study found that the intention of GPs to offer additional vaccination to people aged 60 years and older other than influenza vaccination was mainly predicted by their attitude towards offering additional vaccination, their attitude towards vaccination as a preventive tool in general, and their attitude towards offering vaccination during the outbreak of an infectious disease. On average, GPs seem to be positive about vaccination as a preventive tool in general, but a bit less positive about offering additional vaccination to people aged 60 years and older. Our findings further suggest that GPs are more willing to recommend vaccination against pneumococcal disease, herpes zoster and pertussis to patients in their 60s when those patients have co-morbidities, with the most positive intention for pneumococcal disease. The attitude of GPs to offer additional vaccination was amongst others predicted by the perceived severity of pneumococcal disease and the perceived severity and prevalence of herpes zoster. Research from the US, Australia and Italy has also shown that GPs had a positive attitude towards recommending influenza and pneumococcal vaccination to older patients and that these diseases were perceived to be serious for older people [
17‐
20]. Moreover, research from the United States has shown that GPs recommend herpes zoster vaccination less often to their older patients than they do influenza and pneumococcal vaccination [
21], despite the recognition of GPs that herpes zoster can cause prolonged suffering among older individuals [
22]. This is in accordance with our finding that most GPs indicate the pneumococcal vaccine as the one among the three vaccine candidates with the highest chance to be added to the national program, and that only few GPs consider herpes zoster vaccination and pertussis vaccination for inclusion. This is also in line with the estimated disease burden of the respective diseases [
23], as well as with the prioritization of Dutch older adults, who had indicated the highest acceptance for pneumococcal vaccination and the lowest for pertussis vaccination [
11]. Consequently, the intention of Dutch GPs to offer additional vaccination to older people will probably depend on their perceived severity of the diseases and their disease burden. GPs ranked the severity of an infectious disease most frequently as an important argument for offering vaccination to older people, followed by the effectiveness of the vaccine, and the expected health benefits for the individual. Cost-effectiveness was ranked as the least important argument for offering vaccination. Side effects of the vaccine and the outbreak of an infectious disease were also ranked lower in the importance for the decision to offer vaccination. Previous research from the US had shown that beliefs about vaccine effectiveness, the risk for illness, and cost-effectiveness of a vaccine were strongly associated with the recommendation of pneumococcal vaccination by GPs [
17].
The selection of vaccination for older individuals based on co-morbidities instead of age, also appeared as one of the main predictors of the attitude of GPs to offer additional vaccination to older people. Although it was difficult to interpret its influence since it shows a negative univariate association with attitude to offer additional vaccination, we think that selection on comorbidity is preferred. The contradiction was very likely due to the way the statement was framed: “Vaccinating people on the basis of co-morbidities is favored over vaccinating people on the basis of age, irrespective of the infectious disease” contains a weighing up of two alternatives. In order to better understand this contradiction, we presented this item as two separate statements to a group of GPs (N = 99). Results showed that selection of vaccination for older individuals on the basis of co-morbidity was favored over selection on the basis of age. Attitude to offer additional vaccination to people aged 60 years and older other than influenza was further predicted by their general attitude towards vaccination as a preventive tool, as well as by their attitude towards offering vaccination to patients in their 80s and during the outbreak of a disease.
Moreover, intention was predicted by whether GPs think that they are the suitable professionals to offer additional vaccination to older people. Considering the importance of the role of GPs in expanding the current vaccination program for older people, it is a positive sign that they consider themselves suitable for offering and applying additional vaccination. In the qualitative study preceding this study, GPs explained that they were suitable to implement new vaccination strategies, because of their successful implementation of the influenza vaccination program, their knowledge on the disease histories of their patients, and their role as health educators that are trusted by older patients [
12].
Influenza vaccination uptake rates among older people are suboptimal in Europe [
24]. Previously reported barriers to administering vaccination to adults have been a lack of physicians’ knowledge about vaccination [
25], poor vaccine supply [
26], cost of vaccinations [
27], and practice barriers, such as competing priorities in care especially in the presence of acute or chronic problems [
28,
29]. The most common barriers for vaccination uptake among patients were a lack of knowledge about the benefits of vaccination [
30], concerns about vaccine safety [
31,
32] and when vaccination is not recommended by physicians [
11,
32,
33]. In the light of our findings, it seems to be especially important to inform GPs about available vaccines for older people and to provide them with evidence-based information on the incidence and severity of the targeted infectious diseases among older people. The finding that GPs have a more positive intention to offer pneumococcal, herpes zoster and pertussis vaccination to older patients, when they have a co-morbidity is in line with research showing that co- and multi-morbidity lead to higher susceptibility towards infectious diseases in older people [
4]. However, older age on its own also increases the incidence of serious complications and mortality associated with infection [
4,
34,
35]. Identifying the influence of co-morbidities on the disease burden of infectious diseases poses methodological challenges [
23] since data on the occurrence of comorbidity is often missing. Policy advisers should therefore clearly state evidence-based implications, explaining why recommendation of vaccination is based on age rather than on co-morbidity. For example, research has suggested that vaccination against herpes zoster should be focused on specific age groups, since the disease burden was relatively low for people aged 50 years and older, but increased considerably for people aged 75 years and older [
23].
A limitation that should be mentioned is that the survey length was kept to a minimum and the variables were for the most part measured by one single item, which might have lowered measurement specificity. This was done to achieve a higher response rate. Still, response bias is likely with the low response rate of 6% and we only have limited data to compare participating GPs to the total population of Dutch GPs. Moreover, generalization of the findings to other countries should be treated with caution since vaccination policies, as well as vaccination acceptance differ among countries [
36].
Conclusions
In conclusion, GPs seem to be positive about offering at least some of the additional vaccinations to older people, when infectious diseases are perceived as severe and prevalent. They also feel suitable to administer additional vaccination. In order to ensure a positive attitude of GPs towards informing about and administering additional vaccinations to older people, they need to have clear guidelines, including evidence-based information about severity and incidence of the diseases, the effectiveness and health benefits of the vaccines, as well as about advising vaccination based on high-risk groups.
Acknowledgements
Paul Krabbe from the Univeristy of Groningen, Hermien Vrieze and Ton Drenthen from the Dutch College of General Practitioners (NHG), and Louwrens Boomsma from the National General Practitioner’s Organization (LHV) assisted in the development of the questionnaire. Monique Dayan from the National Influenza Prevention Program Foundation (SNPG) and Joost Timmermans from the National Institute for Public Health and the Environment (RIVM) assisted in the distribution of the questionnaire.