Time is of the essence: exploring a measles outbreak response vaccination in Niamey, Niger

Abstract

The current World Health Organization recommendations for response during measles epidemics focus on case management rather than outbreak response vaccination (ORV ) campaigns, which may occur too late to impact morbidity and mortality and have a high cost per case prevented. Here, we explore the potential impact of an ORV campaign conducted during the 2003-2004 measles epidemic in Niamey, Niger. We measured the impact of this intervention and also the potential impact of alternative strategies. Using a unique geographical, epidemiologic and demographic dataset collected during the epidemic, we developed an individual-based simulation model. We estimate that a median of 7.6% [4.9-8.9] of cases were potentially averted as a result of the outbreak response, which vaccinated approximately 57% (84 563 of an estimated 148 600) of children in the target age range (6-59 months), 23 weeks after the epidemic started. We found that intervening early (up to 60 days after the start of the epidemic) and expanding the age range to all children aged 6 months to 15 years may lead to a much larger (up to 90%) reduction in the number of cases in a West African urban setting like Niamey. Our results suggest that intervening earlier even with lower target coverage (approx. 60%), but a wider age range, may be more effective than intervening later with high coverage (more than 90%) in similar settings. This has important implications for the implementation of reactive vaccination interventions as they can be highly effective if the response is fast with respect to the spread of the epidemic.

Public health responses during measles outbreaks in elimination settings: Strategies and challenges

“…Although this has not been evaluated systematically, evidence supporting supplementary vaccination activities during outbreaks is accumulating. 62 In studies of varying design and in diverse settings, broad and early implementation of vaccination has been associated with shorter outbreak durations, 63 smaller outbreak sizes as determined by mathematical models, 64 , 65 alterations in the shape of epidemic curves and reductions in incident cases, 12 , 66 , 67 lower than expected morbidity and mortality, 66 , 68 and partial or complete avoidance of outbreaks in closed populations. 69 , 70 Yet, in evaluating measles virus transmissibility during outbreaks, it is often difficult to disentangle the relative effects of reactive immunization versus a depletion of susceptible persons from natural infection, or the effects of other control measures (isolation of cases, quarantining or exclusion of susceptible contacts) and of community behavior (e.g., staying home due to illness).…”

The dynamics of measles in sub-Saharan Africa

“…8), was applied on 15 November only to the large Niamey-like patch in response to an outbreak, defined as 10 total cases in October (Supplementary Information B). Given the costs (human, logistic and financial) of mounting such a campaign we assume conservatively that ORV campaigns would not be conducted in consecutive years.…”

“…The continued persistence of measles in these low income, high birth rate countries reflects the challenges of achieving high vaccine coverage in areas with limited public health infrastructure. Major epidemics still occur and Outbreak Response Vaccination (ORV) is one of the strategies that may be deployed to mitigate the immediate morbidity and mortality impact of these occasional outbreaks [5][6][7][8][9][10][11][12] .…”

Research priorities for global measles and rubella control and eradication

“…Successful ORI efforts control measles outbreaks and limit the spread of the virus [56,57,17]. The approach to ORI can vary depending on the level of health service infrastructure, susceptibility by age in the population, the risk for disease spread and severity of clinical complications; debate continues related to optimal timing, target populations, and vaccine delivery methods [58].…”