Varicella seroepidemiology and immunization in a cohort of future healthcare workers in the pre-vaccination era

Objectives: The goal of this study was to establish the seroprevalence of positive antibodies against varicella and compliance with varicella vaccination in the pre-vaccination era. Materials and methods: A cohort of 10,683 Italian students from Padua University Medical School (from 2004 to 2019) was enrolled and classified as unvaccinated, vaccinated once and vaccinated twice against varicella, according to vaccination certificate; the antibody titre was measured, and the seroprevalence of positive subjects was determined. Subjects with negative or equivocal antibodies were invited to vaccinate, and then the antibody titre was retested. Results: Unvaccinated students were mostly seropositive (95.6%) compared with vaccinated students, who were less seropositivity (68.0% after one dose and 78.6% after two doses) and had a significantly (p<0.0001) lower antibody titre. The post-test vaccination had a positive response rate of 85.4%: 67.4% after one dose and 91.4% after two doses. Conclusion: In the pre-vaccination era, only 3.3% of future healthcare workers were vaccinated against varicella (1.1% once and 2.2% twice). Vaccination or revaccination of negative and equivocal subjects can reduce the number of susceptible subjects. Implementation of varicella vaccine (two doses) in healthcare workers is of primary importance to reduce the risk of transmission.