WHO and European guidance explicitly frame catch-up vaccination as a necessary programme function to ensure that individuals who miss routine HPV immunisation are not permanently excluded from protection.
WHO defines catch-up vaccination as vaccinating individuals who are missing doses of vaccines for which they are eligible under the national immunisation schedule, and states that a catch-up vaccination strategy is an essential part of a well-functioning national immunisation programme that should be implemented on a continual basis [1], consistent with a life-course approach to immunisation [2]. Catch-up vaccination can play an important role in closing immunisation gaps that would otherwise widen over timeas populations age, and that individuals who miss vaccination become harder to identify and reach over time [1].
The European Code Against Cancer explicitly recommends providing catch-up opportunities for HPV vaccination to people older than the priority age group, at least until age 18 where feasible, and prioritising individuals at higher risk of HPV infection, including immunocompromised individuals and people living with HIV [3]. The EU Council Recommendation on vaccine-preventable cancers further supports extending recommendations, via targeted catch-up campaigns, to young adults who did not get vaccinated or fully vaccinated during adolescence or preadolescence, reinforcing the role of catch-up as a policy tool to prevent missed cohorts from remaining unprotected over time [5].
Guidance emphasises that decisions to extend HPV vaccination beyond routine target populations should be directed by formal, evidence-informed processes and reviewed over time as programme conditions evolve.
Guidance on planning and implementing catch-up vaccination recommends that National Immunization Technical Advisory Groups (NITAGs) provide technical and programmatic advice on the development and review of vaccination policies and explicitly calls for existing policies to be reviewed and revised where they unintentionally constrain catch-up or extended-age vaccination. This includes restrictive target age groups or upper age limits, limitations on which health workers are authorised to vaccinate, and inflexibility on when and where vaccinations can be delivered [1] and reinforces the importance of periodic policy review that can be adapted over time as programme conditions evolve.
The EU Council Recommendation on vaccine-preventable cancers similarly emphasises structured national action and coherent policy frameworks to support coherent and coordinated vaccination policy, supporting the need for policy decisions that are transparent, coordinated, and capable of review over time in line with national priorities and system capacity [5].
Routine HPV vaccination delivery models may systematically miss certain populations, so targeted or alternative delivery pathways are required to ensure access to vaccination for these groups.
Offering catch-up vaccination to populations who may not be reached through routine immunisation services is critical to ensuring that they are not excluded from protection. This includes mobile populations such as refugees, asylum seekers and migrants, who may be difficult to reach or track and for whom responsibility for vaccination may be unclear, particularly where individuals move across borders [1,2]. The WHO further emphasises that immunisation strategies should be adapted to reach populations that are geographically, socially or culturally isolated, and that addressing the causes of low vaccine use among marginalised groups is necessary to improve access to immunisation services [2].
Specific population groups are identified by WHO and European guidance, for whom targeted HPV vaccination strategies may be appropriate due to elevated risk of HPV infection or disease, or because they are not reliably reached through routine delivery models, such as men who have sex with men (MSM), due to the high burden of HPV infection in this group [4]. In practice, many MSM were not reached through earlier adolescent vaccination programmes because HPV vaccination programmes initially targeted girls, and targeted adult offers may miss people who do not disclose sexual orientation, do not attend sexual health services, or face stigma and discrimination in healthcare settings [6, 7]. Complementary access pathways including delivery through sexual health, HIV prevention and other inclusive services, may therefore be needed [8]. The European Code Against Cancer similarly recommends that individuals at higher risk of infection, including immunocompromised individuals and people living with HIV, are prioritised for HPV vaccination, supporting the use of tailored approaches beyond standard-age delivery [3].
European policy instruments further reinforce the need for dedicated strategies to reach populations missed by routine vaccination pathways. The EU Council Recommendation on vaccine-preventable cancers calls for targeted efforts to address structural barriers to HPV vaccination uptake among disadvantaged groups, explicitly naming migrants, asylum seekers, refugees, people experiencing homelessness, Roma, persons with disabilities, displaced people from Ukraine, LGBTI people, and individuals with higher-risk sexual behaviour [5].
