To assess the immunogenicity, with a focus on the interchangeability of type and route of anti-rabies vaccine, specifically 8 years after the primary PrEP and 5 years after the last booster dose.

This was a longitudinal interventional follow-up study conducted during October 2023 at a biological park situated in southern India. This study included a cohort of 72 participants, working at the biological park. All had received the primary course of PrEP with a purified chick embryo cell vaccine (PCECV) by the intramuscular (IM) route in 2015, followed by annual booster doses of 0.1 mL purified vero cell rabies vaccine (PVRV) in 2016 and 2017 and PCECV (2018) by the intradermal (ID) route. No annual boosters were administered for the next 5 years. In October 2023, a single booster dose of ID PCECV was administered. Rabies virus neutralizing antibody titres were estimated by the rapid fluorescent focus inhibition test (RFFIT) after the booster doses in 2017 (at 2 years) and 2023 (at 8 years) post-primary vaccination.

The majority (34.7%) of participants were in the 41–50 age group, 97.2% were men and 43.1% were animal keepers. The geometric mean titre and geometric standard deviation of the RFFIT titre on day 0 (8 years after initial PrEP) was 2.51 ± 1.73 IU/mL and on day 14 after the booster dose of PCECV was 18.4 ± 1.52 IU/mL.

PrEP booster administration of rabies vaccines demonstrated significant immunogenicity even after 8 years, despite changes in vaccine type and administration route.