- Design
- systematic review and meta-analysis of randomised cohorts, RoB 2 assessed
- Population
- 3,282 children and adolescents across four randomised cohorts, studies concentrated in China
- Primary outcome
- seroconversion rate and geometric mean anti-HAV concentration, with adverse events
- Effect
- seroconversion at 1 month OR 3.05 (95% CI 1.88–4.96); GMC at 7 months SMD 0.88 (0.18–1.58); adverse events RR 0.95 (0.76–1.20)
Seven publications from four randomised cohorts, 3,282 children and adolescents in total, were pooled to compare inactivated hepatitis A vaccines based on the TZ84 strain with those based on HM175.
Seroconversion at one month favoured TZ84-based vaccines (odds ratio 3.05, 95% CI 1.88 to 4.96), as did geometric mean antibody concentration at seven months (standardised mean difference 0.88, 0.18 to 1.58, p = 0.01). Follow-up extending to 186 months — 15.5 years — reported higher anti-HAV concentrations with TZ84-based products. Adverse events were comparable (risk ratio 0.95, 0.76 to 1.20).
The limitations are substantial and the authors list them plainly: only four unique randomised cohorts underlie seven papers, the studies are concentrated in China, heterogeneity is considerable, and every outcome is a surrogate. No study here compared rates of hepatitis A. That matters because both vaccine types produce seroprotection in the great majority of children, and a difference in antibody titre between two effective vaccines is not the same as a difference in disease.
For Indian practice, where hepatitis A vaccination is recommended in childhood and multiple products are available, this is worth knowing when a product choice is genuinely open — and not a reason to revaccinate a child who has already completed a course with either.
- Do not revaccinate a child who has completed a course with an HM175-based vaccine
- Where product choice is open and cost is similar, the immunogenicity data favour TZ84-based vaccines
- Record which product and which dose number was given — series completion matters more than strain
- Treat antibody titre as a surrogate; no study here compared cases of hepatitis A
Why it matters
It gives a basis for choosing between hepatitis A products where one has to be chosen, without implying anything is wrong with the other.
Don't overread it
Every outcome here is an antibody measurement — no comparison of actual hepatitis A infection was made.
The statistics, in plain English
An odds ratio of 3.05 for seroconversion sounds large, but when both vaccines seroconvert most children the absolute difference can be small — an odds ratio compares odds, not percentages, and is inflated when the baseline rate is high. A standardised mean difference of 0.88 for antibody concentration is a moderate-to-large effect on a titre, which need not translate into protection. Four unique cohorts generating seven publications means the evidence is thinner than the citation count suggests.
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