Academic journal article Bulletin of the World Health Organization

Evaluating the Impact of the HIV Pandemic on Measles Control and Elimination

Academic journal article Bulletin of the World Health Organization

Evaluating the Impact of the HIV Pandemic on Measles Control and Elimination

Article excerpt

Introduction

Despite the availability of a safe and effective vaccine against measles, 614 000 measles-related deaths were estimated to have occurred in 2002, making measles a leading cause of childhood death (1). WHO, UNICEF, and other partners have established goals to reduce by half the number of measles deaths by 2005 and to interrupt indigenous measles-virus transmission in large geographical areas (2). To achieve these mortality-reduction goals, a high level of" protection, or population immunity, is required. In areas without circulating measles virus, population immunity is determined by multiplying the proportion of the population vaccinated by the vaccine's effectiveness. In order to achieve a high level of population immunity, control programmes should sustain at least 90% coverage with a first dose of measles vaccine. In addition, a second opportunity for measles vaccination must be provided through routine or supplemental activities and reach at least 90% of children. To eliminate measles in large geographical areas, even higher population immunity may be needed (93-95%) (2-5). Measles control programmes may have little margin for even small increases in the number of susceptible people such as those that may occur in areas of low vaccination coverage or with reduced vaccine effectiveness.

One of the potential obstacles to measles control and elimination is the HIV pandemic (6, 7). Almost half of all measles-related deaths occur in sub-Saharan Africa, and 64% of the world's 40 million people infected with HIV live in the same area (8-10). Infection with HIV may modify the clinical manifestations of measles, thus disrupting case-finding efforts, and HIV infection may also alter the communicability of measles by prolonging the infectious period. Most importantly, HIV infection may result in high rates of primary and secondary measles vaccine failure after immunization, resulting in lower vaccine effectiveness.

Despite these potential barriers, progress towards measles elimination in seven countries in southern Africa shows that excellent control of measles can be achieved in regions with high prevalence of HIV infection. This was accomplished by maintaining high routine vaccination rates (average rate = 80%; range = 61-90%) coupled with high coverage in periodic supplemental campaigns (average = 91%; range = 60-105%) (11). Reported measles-related deaths fell from 166 in 1996 to 0 in 2000 and 2001. Between 2000 and 2002, these countries reported record low levels of measles; between January 2000 and December 2002, less than 10% (492) of 5113 suspected cases of measles for whom blood results were available were serologically confirmed (12-14).

To understand better the interaction between HIV and measles, the factors that have contributed to the success in southern Africa, and what potential barriers might lay ahead, we developed a simple model, applicable to regions in sub-Saharan Africa where there is a high prevalence of HIV, to estimate the impact of the HIV pandemic on population immunity to measles.

Methods

The published literature was reviewed (using MEDLINE and searching keywords including measles, measles vaccination, HIV, AIDS, child mortality) to estimate parameters important in assessing the impact of HIV on population immunity to measles. These parameters included the prevalence of HIV infection in children in sub-Saharan Africa and their likelihood of survival to the age of 5 years, the mode and timing of HIV transmission from mother to infant, the loss of protective maternal antibodies in children born to HIV-infected women, the proportion of HIV-infected children and uninfected children who develop protective immunity following measles immunization, and the duration of this protective immunity.

We constructed a simple model of the impact of the HIV pandemic on population immunity to measles in children less than 5 years old (Appendix 1). …

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