Two hepatitis A vaccine platforms compared, on antibody rather than disease

Design

Systematic review and meta-analysis of seven publications from four randomised cohorts; PROSPERO-registered, Cochrane RoB 2 assessed

Population

3,282 children and adolescents receiving inactivated hepatitis A vaccine, studies concentrated in China

Primary outcome

Seroconversion rate and geometric mean antibody concentration, with adverse events

Effect

Seroconversion at 1 month odds ratio 3.05 (95% CI 1.88-4.96) and antibody concentration at 7 months standardised mean difference 0.88 (0.18-1.58) favouring TZ84; adverse events comparable, risk ratio 0.95 (0.76-1.20)

Inactivated hepatitis A vaccines in use worldwide are built on two different virus strains, TZ84 and HM175, and there has been a long-standing impression that the first produces stronger and more durable antibody responses. This review pooled seven publications from four randomised cohorts, 3,282 children and adolescents in total, to test it.

Seroconversion at one month favoured TZ84-based vaccine (odds ratio 3.05, 95% CI 1.88-4.96), as did geometric mean antibody concentration at seven months (standardised mean difference 0.88, 0.18-1.58). Follow-up extending to 186 months — 15 and a half years — reported higher anti-HAV concentrations with the TZ84-based products. Adverse events were comparable between the two (risk ratio 0.95, 0.76-1.20).

The limitation is structural and the authors state it. Every endpoint here is an antibody measurement, not a case of hepatitis A. Both vaccine types produce seroprotective responses in the great majority of children, and a difference in antibody titre above the protective threshold may mean nothing clinically. The evidence also comes from only four unique randomised cohorts, mostly conducted in China. Where both products are available and priced similarly this is a reason to prefer one; it is not a reason to revaccinate a child who has had the other.

• Do not revaccinate a child already given an HM175-based vaccine on this evidence
• Where both are stocked and cost is similar, the antibody data favour the TZ84-based product
• Remember the endpoints are antibody titres, not hepatitis A cases
• Only four unique randomised cohorts, mostly from one country, underlie the pooled estimates
• Local availability and cost should still drive the choice in practice

Why it matters

It answers a purchasing question, not a clinical one — and the distinction is worth holding when a representative presents the same data.

Don't overread it

Higher antibody titres are not the same as better protection against disease, which this analysis did not measure.

The statistics, in plain English

A standardised mean difference of 0.88 describes a large gap in antibody concentration, but concentration above the seroprotective threshold does not scale into proportionally more protection — the relationship flattens. An odds ratio of 3.05 for seroconversion sounds decisive until you note that seroconversion is high in both arms, so the absolute difference is much smaller than the ratio suggests. These are surrogate outcomes throughout; no clinical infection endpoint was measured.

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