CONTROLLING MEASLES USING SUPPLEMENTAL IMMUNIZATION ACTIVITIES: A MATHEMATICAL MODEL TO INFORM OPTIMAL POLICY

Sunday, 19th of April 2015

 

CONTROLLING MEASLES USING SUPPLEMENTAL IMMUNIZATION ACTIVITIES: A MATHEMATICAL MODEL TO INFORM OPTIMAL POLICY

• Stéphane Verguet^{a, ,} ,
• Mira Johri^{b, c},
• Shaun K. Morris^{d, e, f},
• Cindy L. Gauvreau^f,
• Prabhat Jha^{f, g},
• Mark Jit^{h, i}

• ^a Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, MA, USA
• ^b International Health Unit (USI), University of Montreal Hospital Research Centre (CR-CHUM), Montreal, Québec, Canada
• ^c Department of Health Administration, School of Public Health, University of Montreal, Montreal, Québec, Canada
• ^d Division of Infectious Diseases, Hospital for Sick Children, Toronto, Ontario, Canada
• ^e Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
• ^f Center for Global Health Research, Saint Michaels Hospital, Toronto, Ontario, Canada
• ^g Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
• ^h Modelling and Economics Unit, Public Health England, London, United Kingdom
• ⁱ Department of Infectious Disease Epidemiology, London School of Hygiene and Tropical Medicine, London, United Kingdom

Received 31 August 2014, Revised 17 November 2014, Accepted 27 November 2014, Available online 23 December 2014

Open Access funded by World Health Organization

Under a Creative Commons license

Vaccine,Volume 33, Issue 10, 3 March 2015, Pages 1291–1296

 

Abstract below; full text is at doi:10.1016/j.vaccine.2014.11.050

Background

The Measles & Rubella Initiative, a broad consortium of global health agencies, has provided support to measles-burdened countries, focusing on sustaining high coverage of routine immunization of children and supplementing it with a second dose opportunity for measles vaccine through supplemental immunization activities (SIAs). We estimate optimal scheduling of SIAs in countries with the highest measles burden.

Methods

We develop an age-stratified dynamic compartmental model of measles transmission. We explore the frequency of SIAs in order to achieve measles control in selected countries and two Indian states with high measles burden. Specifically, we compute the maximum allowable time period between two consecutive SIAs to achieve measles control.

Results

Our analysis indicates that a single SIA will not control measles transmission in any of the countries with high measles burden. However, regular SIAs at high coverage levels are a viable strategy to prevent measles outbreaks. The periodicity of SIAs differs between countries and even within a single country, and is determined by population demographics and existing routine immunization coverage.

Conclusions

Our analysis can guide country policymakers deciding on the optimal scheduling of SIA campaigns and the best combination of routine and SIA vaccination to control measles.

1. Introduction

The fourth United Nations Millennium Development Goal aims to reduce under-five mortality rates by two thirds between 1990 and 2015. Despite accelerated progress, with a decline from about 12 million deaths in 1990 to about 7–8 million deaths in 2010, the goal is unlikely to be attained at current rates of decline [1], [2] and [3]. Measles has been a key contributor to this mortality. Although measles mortality has dropped globally, from up to 5% of under-five deaths in 2000 [2], [4] and [5] to about 1–2% in 2010 [2] and [3], measles burden remains high in a number of countries [6]. The Measles & Rubella Initiative (www.measlesrubellainitiative.org), a broad consortium of global health agencies, has provided support to measles-burdened countries in order to sustain and achieve measles mortality reductions. It has been focusing on maintaining high coverage of routine immunization of children at about 9 or 12 months of age and supplementing it by a recommended second dose for measles vaccine [7], [8] and [9]. In a large number of countries, the second dose of measles vaccine is usually included in the vaccination schedule and usually administered to children before school entry [8]. In high measles-burdened countries, often, only one dose is routinely given, but an opportunity for a second dose of measles vaccine is offered through supplemental immunization activities (SIAs) [8] and [9]. During SIAs, children and adolescents are targeted regardless of their previous history of measles vaccination. Periodic SIA campaigns occur nationally/sub-nationally with use of various outreach strategies [9].

World Health Organization (WHO) analysts have reported sustained decreases in measles mortality worldwide since the 2000s [6] and [10]; most recently, global measles-related deaths were estimated to have decreased from about 535,000 deaths in 2000 to 140,000 deaths in 2010 [6]. Despite these global reductions, measles mortality remains substantial and concentrated in a number of high measles-burdened countries [2], [3] and [6]. For example, India accounted for almost 50% (about 65,000 deaths) of estimated measles mortality in 2010, and the WHO Africa region for almost 40% (about 50,000 deaths) [6] and [11]. Some of these countries have low levels of routine immunization, such as Nigeria with a 42% coverage rate for the first dose of measles vaccine (MCV1) [12]. That being said, experience from first the Pan American Health Organization (PAHO) and then sub-Saharan Africa has shown that SIAs can contribute to achieving measles control in high burden countries. Indeed, large-scale implementation of SIAs in the PAHO region since the 1990s is thought to have contributed to the elimination of the endemic transmission of measles in the Americas [13]. The same strategy has been adapted to sub-Saharan Africa and appeared as a major contributor for the reported drops in measles deaths on the African continent over the last decade [14] and [15]. Therefore, it is necessary to examine the optimal strategies that can be implemented in order to control measles in high burden countries; in particular, it is important to determine the appropriate use and frequency of periodic SIAs in these countries.

High measles-burden countries with limited financial resources are confronted with difficult decisions related to measles control. For example, these decisions involve sensitive trade-offs between investing in sustainable routine immunization services and implementing repeated SIAs, as part of the overall strategy. In particular, WHO recommends SIAs to be repeated every 2–4 years for those countries with MCV1 coverage below 80% [8]. In this paper, we examined the trade-offs between routine vaccination coverage and SIA coverage and inter-SIA periodicity in order to achieve measles control. Specifically, we selected countries with the highest measles mortality burden globally [2] and [3], and estimated the optimal scheduling of future measles SIAs in these countries, using a dynamic compartmental model of measles transmission. The aim is to inform country policymakers about the scheduling of SIAs to achieve measles control.