The mpox experience highlights that timely vaccination plays a significant role in managing infectious disease outbreaks. In fact, it is not likely that preventive vaccination was a driver of the outbreak’s decline, as the mpox incidence started to decline before the start of the vaccination program.
Rather, the reason appears to have been that infection-induced immunity in high-risk groups was an important factor explaining the decline. This is why – to be effective in preventing new cases – future vaccination programs need to be implemented fast after the first cases are observed.
This is according to a study – “Factors potentially contributing to the decline of the mpox outbreak in the Netherlands, 2022 and 2023” by Manon R. Haverkate, Inge Jm Willemstein, Catharina E. van Ewijk, et al – that was published in Eurosurveillance.
It can be recalled that mpox concurrently emerged as a health issue with COVID-19; the difference was, it predominantly affected gay, bisexual, and other men who have sex with men (GBMSM).
The Netherlands is a good study here, as it experienced a significant decrease in mpox cases starting in July 2022, following the first reported case on May 20, 2022. By December 31, 2023, a total of 1,294 cases had been documented. The primary preventive vaccination (PPV) program was launched on July 25, 2022, with 29,851 doses administered by April 30, 2023. The overall vaccine uptake rate was 45.8%, with 35.4% of the target population being fully vaccinated. The efficacy of full vaccination in preventing symptomatic mpox was estimated at 68.2%, highlighting the effectiveness of vaccinations despite the outbreak’s natural decline.
In the study, the researchers found no significant reduction in high-risk behaviors among GBMSM attending sexual health centers during the outbreak, suggesting that behavioral changes were not the primary factor in the outbreak’s decline. Instead, immunity acquired through infection among high-risk groups substantially contributed to the decrease in mpox cases.
The researchers recommended various key strategies for managing future mpox outbreaks:
- The importance of prompt vaccination implementation is underscored, advocating for the swift initiation of vaccination programs as soon as initial cases are detected to curb widespread transmission.
- The need for ongoing surveillance, emphasizing the necessity of maintaining vigilant monitoring of mpox cases and high-risk behaviors to inform timely public health interventions.
- The need for a comprehensive evaluation of vaccination program effectiveness, suggesting continuous assessment and adaptation of strategies based on emerging data and population dynamics.
According to the researchers, “the necessity of prompt vaccination efforts to effectively control future mpox outbreaks (needs to be highlighted). Although the vaccine demonstrated substantial effectiveness, its impact was mitigated by the timing of the vaccination rollout. Infection-induced immunity and other factors likely played a significant role in the outbreak’s decline before widespread vaccination.”
