Evaluation of vaccine immunity against tetanus, hepatitis B, measles, mumps, rubella and varicella, in migrant adolescents aged 13 to 18 years arriving in Geneva in 2023.

The recent surge in unaccompanied minor asylum seekers (UMAS) arriving in Switzerland presents significant public health challenges, particularly regarding immunization. Many of these adolescents lack vaccination documentation, requiring catch-up vaccination strategies. This study aimed to evaluate immunity against tetanus, hepatitis B, measles, mumps, rubella and varicella among UMAS upon arrival in Switzerland, to optimize vaccination strategies, and provide protection. This retrospective observational study included 100 UMAS patients followed at Geneva University Hospitals in 2023. Patients received a booster of diphtheria-tetanus-pertussis-inactivated poliovirus vaccine (dTPa-IPV) at the first visit at HUG, followed by serology testing one month later during the second visit. Immunity was defined based on established antibody thresholds. Data on demographics, vaccination history since arrival in Switzerland, and serology for tetanus, hepatitis B, measles, rubella, mumps, and varicella were collected from medical records. Among the 100 UMAS included, 83% originated from Afghanistan, 6% from Burundi, 4% from Somalia, 2% from Eritrea, and the remainder from other countries. The median age was 16 years, and 94% were male. Serological testing on arrival showed that 83% were immune to varicella, whereas immunity to measles was lower at 66%. Immunity rates were higher for mumps (90%) and rubella (89%). Only 22% had protective anti-HBs levels. After administration of a single dTPa-IPV booster, 89% achieved protective tetanus IgG concentrations at one-month follow-up.Conclusion: A substantial proportion of UMAS lacked immunity to measles, hepatitis B, and, to a lesser extent, tetanus and varicella, underscoring the need for systematic catch-up vaccination. Based on these findings, a pragmatic two-visit strategy appears optimal: Visit 1: administer MMR (or MMRV), Tdap-IPV, and hepatitis B vaccines to all UMAS; Visit 2 (after 1 month): repeat MMR (or MMRV) and perform tetanus and hepatitis B serology to guide additional doses. This streamlined approach maximizes early protection while remaining feasible within high-income healthcare settings.