One hepatitis A vaccine strain outperformed the other on antibody response in children

Design

Systematic review and meta-analysis of randomised cohorts

Population

3,282 children and adolescents across four randomised cohorts, largely in China

Primary outcome

Seroconversion rate and geometric mean anti-HAV concentration

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, compared inactivated hepatitis A vaccines built on the TZ84 strain with those built on HM175. Seroconversion at one month favoured TZ84 (odds ratio 3.05, 95% CI 1.88–4.96), as did geometric mean concentrations at seven months (standardised mean difference 0.88, 95% CI 0.18–1.58, P = .01). Follow-up out to 186 months showed higher reported anti-HAV concentrations with TZ84. Adverse events were comparable (risk ratio 0.95, 95% CI 0.76–1.20).

The limitations are stated plainly by the authors and matter more than usual here. Four unique randomised cohorts is a thin evidence base, they were concentrated in China, heterogeneity was substantial, and every outcome is a surrogate — antibody concentration, not hepatitis A cases.

Both vaccine types produce seroprotection in the overwhelming majority of children, which is the reason hepatitis A vaccination works at all. A higher antibody concentration on top of that is of uncertain clinical value. This is a reason to prefer one product where both are available at similar cost, not a reason to revaccinate a child who has already had the other.

• Do not revaccinate a child who has completed a HM175-based course — both strains seroprotect.
• Where the choice is open and cost is similar, the immunogenicity data favour TZ84-based products.
• Keep the two-dose schedule; the comparison held after one and two doses but the schedule is what confers durable protection.
• In India, hepatitis A vaccination decisions are usually driven by availability and out-of-pocket cost rather than strain, and that is a reasonable basis.

Why it matters

Vaccine strain is rarely a prescribing choice, and this says when it might be — and when it plainly is not.

Don't overread it

Every endpoint here is an antibody measurement; no trial compared hepatitis A infections between the two vaccines.

The statistics, in plain English

An odds ratio of 3.05 for seroconversion sounds large, but when both vaccines seroconvert most children the ratio is comparing small residual failure rates and exaggerates the practical gap. The standardised mean difference of 0.88 with an interval running from 0.18 to 1.58 is imprecise — the data are consistent with anything from a small to a very large difference in antibody concentration, and antibody concentration is not the same as protection.

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