Epidemiology of measles and its surveillance performance in the Oromia regional state of Ethiopia: Progress and challenges toward measles elimination goals

For decades, the world has known how to stop measles. A safe vaccine exists that can protect children from a disease that once killed millions. Yet, in many parts of the world, the virus still circulates, hiding in communities where vaccination rates are low or where health systems struggle to reach everyone. To stop the virus completely, health officials need to know exactly where it is, who it is hurting, and when it strikes. This requires a system that acts like a constant net, catching every suspected case and testing it to see if it is truly measles or something else that looks similar. Without this clear picture, outbreaks can grow silently until they are too large to control easily. The goal is not just to treat sick children, but to find the virus before it spreads, eventually driving it to extinction in a region.

In the vast Oromia region of Ethiopia, home to more than 40 million people, researchers recently took a deep look at how this surveillance system is working. They examined records from 2006 to 2024, tracking thousands of children and adults who came to health clinics with fever and a rash. When a person shows these symptoms, health workers take a blood sample to check for measles antibodies. The researchers analyzed the results of these tests to understand who was getting sick, where the outbreaks were happening, and whether the system was catching enough cases to meet global elimination goals. Their work reveals a story of a virus that refuses to disappear, peaking during the dry season and striking hardest at the very young and the unvaccinated, while also exposing gaps in how the region monitors the disease.

The data told a clear story about who is most at risk. Out of nearly 26,000 suspected cases that were tested, about 38 percent were confirmed to be measles. The virus did not discriminate by gender, affecting boys and girls equally, but it showed a strong preference for age and location. Most of the confirmed cases occurred in children under the age of 15, with the typical child being five years old. However, the researchers found something surprising: adults between the ages of 15 and 44 were actually more likely to test positive for measles than children in other age groups. This suggests that a large number of older children and young adults missed out on vaccination in the past and are now vulnerable. The virus also favored rural areas and pastoralist communities, where people often live far from health centers, making it harder to get vaccinated. In contrast, people living in cities were less likely to test positive.

Time played a crucial role in how the disease spread. The researchers observed a distinct seasonal pattern, with the number of cases rising sharply as the dry season began. The peak occurred in February, followed by high numbers in March and April. During these dry, cooler months, the odds of a suspected case actually being measles were significantly higher. This pattern likely stems from how people interact during the dry season; families may gather more closely, and schools are often in session, allowing the virus to jump quickly from one person to another. Conversely, the number of cases dropped during the rainy season, from July to September, when heavy rains and school closures may have reduced contact between children. This cycle repeats year after year, indicating that the virus is not just a sporadic visitor but a persistent presence in the region.

The study also highlighted a critical weakness in the region's ability to track the disease. To effectively monitor measles, health officials rely on two main indicators: finding enough suspected cases to test, and finding enough cases that turn out to be not measles, known as non-measles febrile rash illnesses. This second group is important because it proves that the surveillance system is working hard enough to catch every possible case, not just the obvious ones. The researchers found that, on average, only about 44 percent of the districts in Oromia met the target for finding these non-measles cases. Furthermore, fewer than two-thirds of the districts reported at least one suspected case with a blood sample every year. This means that in many areas, the net is too small, and cases are slipping through the cracks. The situation worsened during the global pandemic in 2020, when lockdowns and reduced access to health care led to a sharp drop in reported cases, likely because sick people stayed home rather than seeking help.

Vaccination status remained the most powerful factor in determining who got sick. Among the people who tested positive for measles, nearly 28 percent had never received a single dose of the vaccine. Another 18 percent had received at least one dose, while the vaccination history of the remaining majority was unknown. The researchers noted that people who had not been vaccinated were about twice as likely to test positive for measles as those who had been vaccinated. This confirms that the vaccine works, but it also points to a problem: many children are missing their shots, and the records for those who do get vaccinated are often incomplete or missing. When a vaccinated person still gets sick, it can happen because the vaccine did not provide full protection, or because the vaccine was stored or handled incorrectly before it was given.

The path forward requires more than just counting cases; it demands a stronger, more connected system. The researchers concluded that to stop measles in Oromia, health officials must improve routine vaccination to ensure every child gets their shots on time. They also need to launch catch-up campaigns for older children and adults who missed out. Crucially, the surveillance system itself needs an upgrade. This means expanding the network of laboratories so that blood samples do not have to travel such long distances to be tested, and introducing rapid tests that can give results quickly at local clinics. By strengthening these links and ensuring that every district is actively looking for cases, the region can move closer to the goal of eliminating measles entirely, protecting the most vulnerable children from a disease that is entirely preventable.