Abstract
During a 2025 hepatitis A outbreak in Portimão, southern Portugal, two Roma communities required different public health responses: whole-community vaccination in Cabeço do Mocho, where hygiene and sanitation conditions were deficient, and mainly reactive household-based vaccination in Vale da Arrancada, where residents had potable water and sanitation. We assessed vaccination effectiveness and the consequences of non-vaccination. We conducted a retrospective comparative observational study nested within an outbreak investigation. Residents were classified as vaccinated only if at least 14 days had elapsed between vaccination and symptom onset; otherwise they were classified as unvaccinated. Infection by vaccination status was compared within each community and overall using Fisher’s exact test. By 23 July 2025, 44 outbreak-related cases had been identified. In Cabeço do Mocho, vaccination coverage was 75/107 (70.1%); infection occurred in 2/75 vaccinated versus 11/32 unvaccinated residents (2.7% vs 34.4%; RR = 0.0776; estimated effectiveness 92.2%; p = 0.000021). In Vale da Arrancada, coverage was 21/70 (30.0%); no vaccinated resident became a case, compared with 8/49 unvaccinated residents (0% vs 16.3%; p = 0.094870). Overall, infection occurred in 2/96 vaccinated and 19/81 unvaccinated residents (2.1% vs 23.5%; RR = 0.0888; estimated effectiveness 91.1%; p = 0.000009). Vaccination was associated with markedly lower hepatitis A infection. Whole-community outreach achieved substantially higher coverage than reactive household-based vaccination, while non-vaccination concentrated cases in both communities. These findings support early context-adapted vaccination strategies in socially vulnerable settings during hepatitis A outbreaks.
Key messages
• Whole-community vaccination in the higher-risk setting achieved greater coverage and was associated with lower hepatitis A infection.
• Considering protection only from 14 days after vaccination, cases were concentrated among non-vaccinated residents in both communities.