Since WHO recommended introduction of at least a single dose of inactivated poliovirus vaccine (IPV) in routine immunisation schedules, there have been global IPV shortages. Fractional-dose IPV (fIPV) administration is one of the strategies to ensure IPV availability. We reviewed studies comparing the effects of fractional with full-dose IPV vaccination to determine when seroconversion proportions with each strategy become similar in children aged 5 years and younger.

In this systematic review and meta-analysis, we searched 16 databases in July, 2019, for trials and observational studies, including ongoing studies that compare immunogenicity and adverse events of fractional-dose (0·1 mL) to full-dose (0·5 mL) IPV in healthy children aged 5 years or younger regardless of study design, number of doses, and route of administration. Screening, selection of articles, data extraction, and risk of bias assessment were done in duplicate, and conflicts were resolved by discussion or arbitration by a third author. We assessed immunogenicity, the main outcome, as proportion of seroconverted participants and changes in geometric mean titres of anti-poliovirus antibodies. Timepoints were eligible for analysis if measurements were done at least 4 weeks after vaccination. Summary estimates were pooled by use of random-effects meta-analysis. Analysis was stratified by study design, type of outcome measure, type of poliovirus, and number of doses given. We assessed heterogeneity using the χ² test of homogeneity and quantified it using the I² statistic. We assessed risk of bias using the Cochrane risk of bias tool, and the certainty of evidence using the Grading of Recommendations Assessment, Development and Evaluation approach. The study is registered with PROSPERO, CRD42018092647.

860 records were screened for eligibility, of which 36 potentially eligible full-text articles were assessed and 14 articles were included in the final analysis: two ongoing trials and 12 articles reporting on ten completed studies. For poliovirus type 2, there were no significant differences in the proportions of seroconversions between fractional and full doses of IPV for two or three doses: the risk ratio for serconversion at one dose was 0·61 (95% CI 0·51–0·72), at two doses was 0·90 (0·82–1·00), and at three doses was 0·95 (0·91–1·00). Geometric mean titres (GMTs) for poliovirus type 2 were lower for fIPV than for full-dose IPV: −0·51 (95% CI −0·87 to −0·14) at one dose, −0·49 (−0·70 to −0·28) at two doses, and −0·98 (−1·46 to −0·51) at three doses. The seroconversion meta-analysis for the three-dose comparison was homogeneous (p=0·45; I²=0%), whereas heterogeneity was observed in the two-dose (p<0·00001; I²=88%) and one-dose (p=0·0004; I²=74%) comparisons. Heterogeneity was observed in meta-analyses of GMTs for one-dose (p<0·00001; I²=92%), two-dose (p=0·002; I²=80%), and three-dose (p<0·00001; I²=93%) comparisons. Findings for types 1 and 3 were similar to those for type 2. The certainty of the evidence was high for the three-dose comparisons and moderate for the rest of the comparisons.

There is no substantial difference in seroconversion between three doses of fIPV and three doses of full-dose IPV, although the full dose gives higher titres of antibodies for poliovirus type 1, 2, and 3. Use of fractional IPV instead of the full dose can stretch supplies and possibly lower the cost of vaccination.

South African Medical Research Council and the National Research Foundation of South Africa.