The burden of vaccine preventable diseases (VPDs) is threatening healthcare systems not only by an increasing number of ageing people (50 years and older) but also through the age-related decline of the immune system (1, 2). As a preventive strategy, vaccination has been reported to be effective in limiting the severity, reducing morbidity, and mortality of infections in ageing population (3-5).

However, vaccines are underutilized in ageing population characterized by delayed policy implementation and low vaccine uptakes. This issue is partly demonstrated by less than two third of European countries having policies for pneumococcal vaccine and most countries having no vaccination policies against herpes zoster (6).

Therefore, countries need to strengthen their immunization programs for ageing population by focusing on both decision-making and implementation aspects.

It is known that one of the required elements for both processes is evidence, including international literature and country-specific evidence (7). However, questions are raised on which evidence will be needed and what types of studies should be conducted to support decision-makers in introducing vaccines for ageing adults. In many countries, there is no transparent guidance that presents these methodological requirements (7).

Acknowledging those gaps, Work package 3 (WP3) in the VITAL project has constructed a Country score tool that serves as a readiness assessment to first, identify the gaps in healthcare systems concerning ageing adult immunization programs; and second, to identify methods for future research enabling decision-making and implementation. The tool was developed in two phases.

In phase 1, a modified Delphi process was used. This method concerns a group consensus strategy that systematically uses a literature review, opinions of the research team and the judgment of experts within the research field to reach agreement (8, 9). The Delphi panel included researchers, supra-national and national decision-makers of immunization programs recruited from five countries. The consensus was predefined at the agreement rate of 70%.


  1. Esposito S, Franco E, Gavazzi G, de Miguel AG, Hardt R, Kassianos G, et al. The public health value of vaccination for seniors in Europe. Vaccine. 2018;36(19):2523-8.
  2. Talbird SE, La EM, Carrico J, Poston S, Poirrier J-E, DeMartino JK, et al. Impact of population aging on the burden of vaccine-preventable diseases among older adults in the United States. Human vaccines & immunotherapeutics. 2021;17(2):332-43.
  3. McElhaney JE, Beran J, Devaster J-M, Esen M, Launay O, Leroux-Roels G, et al. AS03-adjuvanted versus non-adjuvanted inactivated trivalent influenza vaccine against seasonal influenza in elderly people: a phase 3 randomised trial. The Lancet Infectious Diseases. 2013;13(6):485-96.
  4. Yin M, Huang L, Zhang Y, Yu N, Xu X, Liang Y, et al. Effectiveness and safety of dual influenza and pneumococcal vaccination versus separate administration or no vaccination in older adults: a meta-analysis. Expert review of vaccines. 2018;17(7):653-63.
  5. Bonten MJ, Huijts SM, Bolkenbaas M, Webber C, Patterson S, Gault S, et al. Polysaccharide conjugate vaccine against pneumococcal pneumonia in adults. The New England journal of medicine. 2015;372(12):1114-25.
  6. Tan L. Adult vaccination: Now is the time to realize an unfulfilled potential. Human vaccines & immunotherapeutics. 2015;11(9):2158-66.
  7. European Centre for Disease Prevention and Control. Current practices in immunisation policymaking in European countries. Stockholm: ECDC; 2015.
  8. Monguet JM, Trejo A, Martí T, Escarrabill J. Health Consensus: A Digital Adapted Delphi for Healthcare. International Journal of User-Driven Healthcare (IJUDH). 2017;7(1):27-43.
  9. Nasa P, Jain R, Juneja D. Delphi methodology in healthcare research: How to decide its appropriateness. World J Methodol. 2021;11(4):116-29.