More schooling lessens risk of contracting HIV

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AIDSLonger secondary schooling substantially reduces the risk of contracting HIV, particularly for girls, according to new research from Botswana. The researchers estimate that pupils who stayed in school for an extra year of secondary school had an 8 percentage point lower risk of HIV infection about a decade later, from about 25% to about 17% infected.

The study, which also shows expanding secondary schooling to be a very cost effective HIV prevention measure, used a recent school policy reform as a “natural experiment” to determine the impact of increased years of secondary schooling on risk of HIV infection.

Implemented in 1996, the reform led to an average increase of 0.8 years of schooling among teenagers, by providing free grade 10 education as part of junior – rather than senior – secondary school. This policy presented a unique opportunity to estimate the causal effect of length of schooling on risk of HIV infection by comparing birth cohorts exposed to the reform versus those unexposed, using data from national HIV surveys collected in 2004 and 2008.
Although education is known to be closely associated with health, whether or not formal education actually protects against HIV infection has been hotly debated for over two decades. Research so far has produced conflicting results.

Jacob Bor, senior author and assistant professor of global health at Boston University School of Public Health explains, “It is difficult to isolate the effect of education on HIV risk from the complex web of co-factors such as personal motivation, psychological traits, socioeconomic status, and family background. In the absence of large-scale trial data, natural experiments can provide robust evidence to guide policy.”

Using data from two nationally representative household surveys, the Botswana AIDS Impact Surveys (2004 and 2008), the researchers used statistical techniques commonly used in economics and political science to analyse natural experiments. Botswana has one of the highest rates of HIV in the world, with around 22% of adults aged 15-49 years infected in 2013. The authors investigated the causal effect of an additional year of schooling on HIV status in 7018 men and women at least 18 years old at the time of the surveys. Individuals born in or after 1981 (who would have started junior secondary school in 1996 or later) were classified as exposed to the reform.

The researchers estimate that individuals who gained an extra year of secondary schooling due to the policy were 8 percentage points less likely to test positive for HIV about a decade later, when most of those exposed to the policy were in their mid 20s. The effects were particularly strong among women, with each additional year of secondary schooling reducing infection risk by 12 percentage points.

According to co-author Jan-Walter de Neve, a doctoral student at Harvard TH Chan School of Public Health, “Information about prevention methods and reasoning skills gained in school may play a preventative role against HIV, enabling people with education to adopt healthy strategies to avoid infection. Additionally, education may expand economic opportunities and reduce women’s participation in higher risk transactional sexual relationships. Secondary schooling may be particularly effective in reducing HIV risk by targeting a critical period of growth in adolescence.”

The findings also show that increasing secondary schooling has the potential to be a very cost-effective as an HIV prevention intervention in endemic countries. Bor adds, “this study is among the first to provide causal evidence that secondary education is an important causal determinant of HIV infection. Our results suggest that schooling should be considered alongside other proven interventions as part of a multi-pronged ‘combination’ HIV prevention strategy. Expanding the opportunities of young people through secondary schooling will not only have economic benefits but will also yield health benefits and should be a key priority for countries with generalised HIV epidemics.”

An estimated 2•1 million individuals are newly infected with HIV every year. Cross-sectional and longitudinal studies have reported conflicting evidence for the association between education and HIV risk, and no randomised trial has identified a causal effect for education on HIV incidence. We aimed to use a policy reform in secondary schooling in Botswana to identify the causal effect of length of schooling on new HIV infection.
Data for HIV biomarkers and demographics were obtained from the nationally representative household 2004 and 2008 Botswana AIDS Impact Surveys (N=7018). In 1996, Botswana reformed the grade structure of secondary school, expanding access to grade ten and increasing educational attainment for affected cohorts. Using exposure to the policy reform as an instrumental variable, we used two-stage least squares to estimate the causal effect of years of schooling on the cumulative probability that an individual contracted HIV up to their age at the time of the survey. We also assessed the cost-effectiveness of secondary schooling as an HIV prevention intervention in comparison to other established interventions.
Each additional year of secondary schooling caused by the policy change led to an absolute reduction in the cumulative risk of HIV infection of 8•1 percentage points (p=0•008), relative to a baseline prevalence of 25•5% in the pre-reform 1980 birth cohort. Effects were particularly large in women (11•6 percentage points, p=0•046). Results were robust to a wide array of sensitivity analyses. Secondary school was cost effective as an HIV prevention intervention by standard metrics (cost per HIV infection averted was US$27 753).
Additional years of secondary schooling had a large protective effect against HIV risk in Botswana, particularly for women. Increasing progression through secondary school could be a cost-effective HIV prevention measure in HIV-endemic settings, in addition to yielding other societal benefits.

The Lancet material
The Lancet Global Health article

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