What’s the best way to divvy up a shipment of medicine that will cover less than half the people per year than should ideally be reached to end Aids in South Africa? That’s what public health experts discussedat a meetingorganised by the health department and the country’s national Aids council, Sanac, in October about how to allocate the batch of lenacapavir (LEN) shots South Africa is getting, thanks toa donation of $29.2-million (about R500-million at the latest exchange rate) by the Global Fund. The money can buy enough doses of the new six-monthly HIV prevention jab, which is almost foolproof in protecting people from getting infected with HIV through sex, to cover about 456 000 people over two years.
Butmodelling resultspresented at the meeting in October show that up to four times as many people — between one and two million — will have to take the medicine every year at least once if the country wants to get new HIV infections down so low that 15 years from now Aids won’t be a public health worry anymore. Because of the limited initial supply, the medicine will have to “be managed strategically”,saidHealth Minister Aaron Motsoaledi, adding that for the roll-out of LEN over the next two years to make a real difference in the country’s HIV infection rates, the focus has to be “on those populations at highest risk”. These groups,modelling showed, are: female sex workers; gay and bisexual men; teen girls and young women; and pregnant or breastfeeding women.
But who should get what slice of the pie once the medicine is available in public clinics? And are numbers alone what would drive decisions? To get a sense of what the result would be of splitting the available batch of shots among the four target groups in different ways, researchers used acompartmental mathematical model(Thembisa) to run some numbers.
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This is basically an equation made up of a bunch of calculations using specific input values, with the combined answer being an estimate of a certain outcome in real life — in this case, the number of new infections that could be prevented by different groups of people getting the six-monthly anti-HIV injection. And because it’s easy to change the input values — in this case, the proportion of the batch of medicine going to different groups of people — the effect of many different combinations can be forecast. “Modelling is sometimes somewhere between an art and a science,” says Lise Jamieson, who headed the study presented at the meeting.
But because the model uses maths to describe real-life information based on plausible underlying assumptions, it’s a good way to get an informed conversation started — with numbers to back it up, she says. The model, which generated 490 combinations, showed that if just over half of the available shots are given to pregnant women and breastfeeding moms, about a quarter to gay and bisexual men, and around a fifth to female sex workers (scenario A), there could be 20 554 fewer new HIV infections over the next five years.
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