Immunogenicity and safety of polio vaccines in infants: a systematic review of randomized clinical trials

Poliomyelitis, preventable only through vaccination, remains a global health concern, with wild poliovirus transmission and the emergence of vaccine-derived polioviruses. The risk of further deterioration of the situation jeopardizes efforts to eradicate polio, which has been a long-term goal for the whole world. In this systematic review, an analysis of randomized clinical trials was carried out to comprehensively assess the immunogenicity and safety of various polio immunization methods in infants. Geometric mean neutralizing antibody titers (GMT) data collected after 28–31 days after immunization were used to calculate the geometric mean titer ratio (GMR), the analysis of which showed that both inactivated polio vaccine (IPV) and Sabin strain-based inactivated polio vaccine (sIPV) as primary vaccination induce high antibody rates. Average GMR rates (CI = 0.05) for the 3 types of polio were 83.08, 33.60, and 166.30 for IPV and 234.35, 44.04, and 163.13 for sIPV, with fractional IPV showing similar results. One or two doses of IPV were insufficient to induce protection levels of antibodies against type 2 poliovirus. The novel oral polio vaccine type 2 (nOPV2) and trivalent oral polio vaccine (tOPV) also demonstrated immunogenicity in establishing immunity comparable to the inactivated vaccine; the latter exhibited an average GMR of 50.75 for serotype 2. High antibody levels were also induced by combined vaccine schedules, with sIPV-sIPV-bOPV (GMR of 1,172.7 for type 1 and 887.6 for type 3) and IPV combinations with diphtheria-tetanus-whole-cell pertussis, hepatitis B and Haemophilus influenzae type b (351.2, 258.8, and 573.6 for the 3 types) or pentavalent rotavirus vaccine (354.6, 117.7, and 540.9 for the 3 types) establishing particularly high antibody levels. Analysis of adverse events presented all vaccines to be well-tolerated and safe, with a tendency for combination vaccines to have a higher frequency of local reactions and fever. While the studies presented a diverse landscape with some existing areas of concern, this review provides structured evidence supporting the safety and immunogenicity of existing polio vaccines, as well as highlighting the interchangeability of different vaccination approaches in infants. Future research should aim to provide detailed reporting of adverse events in order to facilitate more comprehensive assessment of vaccine immunogenicity and, therefore, efficacy.