Sustained and indirect effects of PCV10 reduced-dose schedules on pneumococcal carriage in Viet Nam: a long-term follow-up of a cluster-randomised controlled trial.

Summary

In a 24-commune cluster-randomised trial (N=49,644) in Viet Nam, a reduced two-dose PCV10 schedule (1p+1) sustained non-inferior control of vaccine-type nasopharyngeal carriage versus three-dose schedules over 5.5 years and generated comparable indirect protection in unvaccinated caregivers. The 0p+1 schedule met non-inferiority in most comparisons, and no vaccine-related serious adverse events were observed.

Key Findings

• 1p+1 PCV10 remained non-inferior to 2p+1 and 3p+0 for vaccine-type carriage at 5.5 years.
• Comparable declines in vaccine-type carriage were observed in vaccinated children and unvaccinated adult caregivers, indicating sustained indirect effects.
• The 0p+1 schedule achieved non-inferiority in 7 of 8 intention-to-treat comparisons; no vaccine-related serious adverse events occurred.

Clinical Implications

Health systems can consider transitioning to a 1p+1 PCV10 schedule (with appropriate catch-up) without compromising indirect protection, potentially reducing program complexity and costs.

Limitations

• Primary endpoint was nasopharyngeal carriage rather than invasive disease incidence
• Generalizability may depend on established programs with catch-up campaigns; some comparisons had small numbers at later timepoints

Future Directions

Assess impact on invasive pneumococcal disease, cost-effectiveness across settings, and applicability to newer PCVs and serotype replacement dynamics.