Prof Colleen Aldous: Measles is moving through South Africa. Is our response moving with it?

Prof Colleen Aldous warns that South Africa's measles outbreak has entered a new phase. Confirmed cases have topped 4,188, but the real story is where they are occurring: infections are spreading beyond the Western Cape into every province, while more than one in five cases now involve people older than 15. Aldous argues this shifting pattern, backed by early wastewater detections, demands a faster, more targeted vaccination response rather than blanket campaigns. Without better public data on who outbreak interventions are reaching, she says, South Africa risks fighting an outbreak that has already moved on..By Prof Colleen Aldous.Two weeks ago, the most important question raised by South Africa’s measles outbreak was why so many children were not being vaccinated. The latest surveillance data raise a different question. Are we responding to the outbreak we have now, or the outbreak we thought we had?The latest report from the National Institute for Communicable Diseases (NICD), published on 9 September and covering cases up to 30 August, records 4,188 laboratory-confirmed measles cases since the end of December 2025. That is almost 300 more cases than were recorded two weeks before. But the cumulative number is no longer the most interesting part of the story. It is where those cases are occurring, and in whom. Measles is moving.The Western Cape still has by far the largest cumulative burden, with 1,366 confirmed cases. But it no longer dominates the weekly increase. In the latest reporting week, Limpopo recorded 22 new cases, Gauteng and the Northern Cape 21 each, KwaZulu-Natal 17 and the Free State 16. Every province recorded new infections. Look below provincial level and the picture becomes even more instructive. During the four weeks to 30 August, Cape Town recorded 73 new cases. John Taolo Gaetsewe district in the Northern Cape recorded 62, Mopani in Limpopo 30, Tshwane 29, Thabo Mofutsanyana in the Free State 26, Waterberg 23 and Amajuba in KwaZulu-Natal 17. A new outbreak was declared in Namakwa. Yet Johannesburg, despite having accumulated 216 cases during the wider outbreak, recorded no new cases during those four weeks. This is what an epidemic looks like when national totals are unpacked. It is not one uniform wave sweeping across the country. It is a collection of local outbreaks that accelerate, slow down and shift geographically. The response should move with the epidemiology.The NICD now recommends provincial measles risk assessments, targeted or supplementary immunisation activities in areas of low coverage, particularly in zero-dose and under-vaccinated communities, as well as mass vaccination campaigns targeting children up to 15 years where required. Very sensible. We now need to ask a another question. Are those interventions reaching the places where transmission is actually increasing, and are they stopping it?The age profile is changing tooThere is another striking feature in the latest report. Children aged one to 14 still account for most confirmed infections with 2,811 of the 4,188 cases, or 67.1% being children. But 506 cases occurred in infants under one year, while 870 occurred in people older than 15. More than one in five confirmed cases is occurring above the age of 15, and 424 cases have been recorded in people aged 30 or older. This should pique our interest a little more than it has up til now.South Africa's childhood immunisation programme gives the combined measles-rubella vaccine at six months and again at 12 months. The NICD records 375 cases in its zero-to-six-month category. Because that category includes six-month-old infants, we cannot tell from the published table precisely how many became infected before they were old enough for their first routine dose. This number makes it clear that very young infants are being affected in this outbreak.They cannot all be protected simply by telling parents to take them for routine vaccination. Young infants also depend on the immunity of the population around them and on antibodies acquired from their mothers early in life. This is where the adult cases become relevant.The WHO's 2025 guidance on measles vaccination campaigns specifically warns against automatically using traditional childhood age bands when the epidemiology shows susceptibility elsewhere. It recommends that campaign age ranges be determined from the actual distribution of cases and population immunity. The WHO states that immunity gaps in older age groups can sustain transmission. They may leave more infants without adequate maternal antibody protection because if the mothers don’t have antibodies, they will not pass them on to their babies through breast feeding.This does not mean South Africa should now embark on indiscriminate adult measles vaccination. The present data do not justify that conclusion. We do not know from the weekly report whether the adult cases occurred predominantly among people who were never vaccinated, received only one dose, had uncertain records, or represent the relatively small number of infections that can occur despite previous vaccination.That missing information is now important. If more than 20% of confirmed cases are occurring above 15 years of age, we should know the vaccination status, age distribution and geographical clustering of those cases. The WHO outbreak guidance recommends precisely this kind of analysis when deciding which age groups should be included in outbreak vaccination. We need to clarify whether the data show an adult immunity gap large enough to alter the outbreak response.South Africa has another early-warning systemWastewater surveillance in the NICD report deserves more attention. Measles virus was detected in wastewater in Gauteng, the Western Cape and Free State during epidemiological week 33. Most interestingly, measles was detected in wastewater in Ekurhuleni even though no clinical case had been identified there during that week. Wastewater cannot tell us who is infected. It cannot determine vaccination status and it cannot replace clinical diagnosis. But it can tell health authorities that the virus is circulating where conventional case reporting may not yet be showing it. That creates an opportunity.South Africa can increasingly combine clinical cases, laboratory confirmation, wastewater signals, local vaccination coverage and district-level outbreak data. Those streams of information could allow health departments to identify emerging hotspots and deploy vaccination teams before the case count becomes large. That is a much more sophisticated public-health response than waiting for a province-wide number to rise and then urging everybody to vaccinate.Show us the response as well as the outbreakThis is where the next stage of accountability should lie. The NICD gives us increasingly detailed information about where measles is occurring. What the public needs alongside it is equally accessible information about the intervention. For each significant outbreak area, we should know how many children were targeted, how many were actually reached, what proportion of cases had received zero, one or two doses, whether particular age groups are disproportionately affected and whether case numbers declined after the campaign.The Western Cape provides an indication of why this matters. It reported that targeted campaigns conducted between October 2025 and March 2026 vaccinated 39,939 people in affected areas. Yet Cape Town remains the country's largest cumulative focus of measles transmission. That does not mean the campaigns failed. Without them, the outbreak might have been considerably worse. But numbers vaccinated are not, by themselves, measures of outbreak control. We need to know who was reached, what proportion of the susceptible population that represented, and what happened afterwards..Read more:.Prof Colleen Aldous: Measles is back and South Africa is asking the wrong question..South Africa already possesses sophisticated laboratory surveillance, increasingly granular geographical reporting and an emerging wastewater surveillance capacity. The challenge is to turn those data into a visibly adaptive response.The first lesson of this measles resurgence was that too many children were falling through the immunisation system. The second is now becoming clear. Outbreaks do not stand still. Their geography changes. Their age distribution can change. The populations requiring intervention may change with them. Our vaccination response needs to change just as quickly. Measles is moving. Public health response needs to move faster..Sign up for your early morning brew of the BizNews Insider to keep you up to speed with the content that matters. The newsletter will land in your inbox every morning on weekdays. Register here.Support South Africa's bastion of independent journalism, offering balanced insights on investments, business, and the political economy, by joining BizNews Premium. Register here.If you prefer WhatsApp for updates, sign up to the BizNews channel here.

Prof Colleen Aldous: Measles is moving through South Africa. Is our response moving with it?

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