RESUMO
Aims: This study was designed to verify the immunogenicity (potency) and the safety of tetanus toxoid vaccines marketed in three large open drug markets in South-Eastern Nigeria. Methodology: Tests for Sterility, formaldehyde concentrations, specific toxicity, endotoxin, and immunogenicity (potency) were conducted on three different brands of tetanus toxoids (Brand α - from Ariaria Drug Market, Aba-Abia State; Brand β - from Ogbete Drug Market, Enugu State; and Brand γ - from Bridge-Head Drug Market, Onitsha-Anambra State). Results: All vaccine brands studied passed the sterility testing, but did not comply with the 2011 BP specifications on free formaldehyde concentration, which stipulates that the free formaldehyde concentration should not exceed 0.02%. The three vaccine brands did not show specific, abnormal, or general toxicity, but contained different amounts of endotoxins. The result of the potency testing showed that the three brands were immunogenic and elicited specific antibodies against tetanus toxin; but brand γ was the most immunogenic since it elicited the highest titers of total IgG, IgG1, and IgG2a followed by brand α, and then brand β. Conclusion: Generally, the quality control tests carried out on these three commercial brands of tetanus toxoids marketed in Nigeria showed that they do not comply with all the pharmacopeial standards on quality and safety required for vaccines of this nature. Therefore, we conclude that some of the tetanus toxoids marketed in open drug markets in Nigeria are substandard and may be responsible for the failures of these vaccines used for immunization in the country.