Optimal Timing Regularly Outperforms Higher Coverage in Preventative Measles Supplementary Immunization Campaigns.

Area of Science:

• Public Health
• Epidemiology
• Vaccination Programs

Background:

• Measles poses a significant threat to global child health, with routine immunization systems in many countries failing to prevent large outbreaks.
• Measles supplementary immunization activities (SIAs) are crucial for controlling the disease, but their effectiveness is debated.
• Current standards emphasize achieving high coverage (≥95%) in SIAs, potentially delaying campaign implementation.

Purpose of the Study:

• To evaluate the trade-off between campaign timeliness and coverage in measles SIAs.
• To determine optimal strategies for measles SIA timing, especially in areas with weak routine immunization.
• To assess the reliability of coverage metrics in evaluating SIA performance.

Main Methods:

• Modeling the impact of different SIA timing and coverage scenarios on measles outbreak risk.
• Comparing the performance of timely, lower-coverage SIAs with delayed, high-coverage SIAs.
• Analyzing the relationship between coverage levels and outbreak prevention.

Main Results:

• A significant trade-off exists between the timeliness and coverage achieved in measles SIAs.
• Optimal SIA timing, even at coverage levels as low as 50%, can outperform delayed campaigns with higher coverage (e.g., 95%).
• Relying solely on measured coverage can be a misleading indicator of SIA effectiveness.

Conclusions:

• Rethinking programmatic standards for measles SIAs is necessary to prioritize timely implementation.
• Lower-coverage, timely campaigns may be more effective in preventing measles outbreaks than delayed, high-coverage campaigns in certain contexts.
• Coverage metrics should be considered alongside timeliness for a comprehensive evaluation of SIA success.