Suppressant effect of human or equine rabies immunoglobulins on the immunogenicity of post-exposure rabies vaccination under the 2-1-1 regimen: a field trial in Indonesia. MAS054 Clinical Investigator Group.

The research study investigates the suppressant effect of human or equine rabies immunoglobulins on the immunogenicity of post-exposure rabies vaccination. The results confirm that rabies immunoglobulins do suppress immune response and thus, WHO’s reference protocol for post-exposure rabies vaccination should be maintained.

Study Overview and Structure

• The study is a field trial conducted in Indonesia to observe the suppressant effect of rabies immunoglobulins on the effectiveness of the post-exposure rabies vaccination.
• The research adhered to the World Health Organization’s (WHO) protocol for post-exposure rabies vaccination, which advises for five intramuscular injections on specific days (0, 3, 7, 14, and 30). Rabies immunoglobulins (RIG) must be given to serious exposure cases graded as III severity.
• The study divided the subjects into three groups: one group received regular Vero-cell rabies vaccines according to the 2-1-1 schedule (days 0, 7, and 21), the other two groups received the same vaccine schedule alongside either equine rabies immunoglobulins (ERIG) or human rabies immunoglobulins (HRIG).

Study Findings

• The results confirmed that adding immunoglobulins does suppress the immune response, in particular, human immunoglobulins showed a more pronounced suppressant effect than equine ones.
• In both groups that received the rabies immunoglobulins, the seroconversion rates (the development of specific antibodies in response to the introduced antigen) did not reach 100% on the 28th day, and the geometric mean antibody titre (average level of antibodies in the blood) was lower than expected.
• The findings substantiate the WHO’s recommendation in their 1992 protocol, which advised including immunoglobulins for severe cases. The results also support the idea of sticking to the 5-injection schedule rather than the alternative 4-injection (2-1-1) schedule, particularly for grade III exposure situations.

Recommendations and Conclusions

• If the physician decides to opt for the 2-1-1 regimen and suggests including immunoglobulins, the preference should be given to purified equine RIG as it has a lesser suppressant effect and is also cost-effective compared to human RIG.
• The findings highlight the importance of adhering to WHO’s recommendation for post-exposure rabies vaccination, especially for severe cases, so as to ensure effective immunogenic response.