Two-year immunogenicity of a pre-exposure rabies vaccination administered as a two-dose schedule
Abstract
Rabies pre-exposure prophylaxis (PrEP) relies on the vaccination of individuals at high risk of exposure, including subpopulations in highly endemic settings with limited access to timely and adequate post-exposure prophylaxis, individuals at occupational risk and travellers who may be at risk of exposure. The latest WHO position paper in 2018 recommends shortening the previous three-dose intramuscular (IM) regimen (Day 0, Day 7 and Day 21) to a two-visit, one-site IM or two-visit, two-sites intra-dermal (ID) administrations, 7 days apart.1 The immunogenicity of these shortened regimens has been assessed mainly in the short term (Days 21 to 35 after the vaccine) or after a booster at 1 year post-vaccination.2,3 In 2019, in the context of severe shortage of the two rabies vaccines available in France for PrEP and post-exposition prophylaxis, a cohort of 228 students from the National Veterinary School of Toulouse (ENVT) received for PrEP this two-visit, one-site IM administrations of rabies vaccine (Rabique Pasteur®) 7 days apart in March 2019 at the vaccination centre of the Toulouse University Hospital, following WHO recommendations. Students were asked to perform a post-vaccination rabies antibody test that was initially planned at 1 year, but was however postponed to May 2021 because of the coronavirus disease 2019 pandemic. Our aim was to assess the long-term immunogenicity of this shortened PrEP regimen. For the purpose of this study, we collected the results of this rabies serology. Participants were included if they had never been vaccinated against rabies before March 2019 (although a serology was not systematically performed to exclude a previous vaccination). The determination of rabies virus neutralizing antibody (RVNA) titer was performed by Rapid Fluorescent Focus Inhibition Test (RFFIT) at the Institut Pasteur of Paris. Students were considered to be protected against rabies (seropositive) if their sera titers were ≥0.5 IU/ml, and seronegative when their sera titers were <0.5 IU/ml. This retrospective cohort study was approved by an institutional review board (RnIPH 2021-89), in accordance with the French data protection authority (MR004, Commission Nationale de l’Informatique et des Libertés, number 2206723v0).