Long-term immunity and the effect of one or two booster doses with a lyophilized human rabies vaccine (human diploid cells) at 10 years post primary vaccination in China

Background: To evaluate the persistence of antibody for 10 years, and investigate the effect of one or two booster doses with Kanghua human diploid cells rabies vaccine (HDCV) in China. Methods: Participants were re-recruited at year 10 post the primary phase 3 clinical study. Some of them in Kanghua HDCV group who had been boosted one dose at year 8, received one more dose at this boosted study. Participants who never boosted were randomly assigned to boost 1 or 2 doses of Kanghua HDCV. Blood samples were collected at day 0, 1, 3, 7, and 14. Safety was evaluated from day 0-14. Results: At year 10 after primary vaccination, the seroconversion rates of neutralizing antibody were 98.28-100% in Kanghua and Pasteur groups. After booster, the seroconversion rate in each group reached to 100% from day 7 to day 14. GMCs were similar in the groups with the same booster doses, and two doses of booster induced higher levels of antibody. The reported rates of solicited local and systemic adverse reaction were low, and no serious adverse events were found through the boosted study. Conclusion: 5 doses of Kanghua HDCV maintained long-term immunity at least 10 years. One or two doses of booster, rapidly triggered 100% protection against rabies virus.