The authors, Harris Bendel of Roskilde University’s PandemiX Center and Katarina L. Matthes of the University of Zurich’s Institute of Evolutionary Medicine, contend that contemporary studies of measles-induced immune amnesia face structural obstacles that historical data can circumvent. In high-income countries today, measles is so rare that the few people who contract it are inherently unrepresentative of the broader population, introducing severe selection bias. In regions where measles remains common, unequal access to healthcare complicates the assembly of reliable study cohorts. Observational studies in wealthy nations are further confounded by pre-existing conditions and differences in healthcare-seeking behavior, making it difficult to isolate the virus’s effect on subsequent mortality.

These methodological problems matter because the stakes of the debate are enormous. Some researchers have suggested that measles immune amnesia may have contributed to as much as half of all childhood deaths from infectious diseases in the period before vaccination. That figure traces back to a widely cited 2015 study by Mina and colleagues, who quantified the drop in non-measles infectious disease mortality in three countries before and after measles vaccines were introduced. The commentary’s authors argue that this approach falters when applied to Denmark, one of the countries in the analysis, because the data used came from a period when infectious disease mortality had already fallen to historic lows.

The numbers illustrate the problem starkly. In 1986, the year before the measles vaccine was introduced in Denmark, there were just 19 deaths from non-measles childhood infections; five years later, in 1991, there were 16. By the 1980s, many of the most significant killers of children, from tuberculosis to diphtheria, had already been largely tamed by sanitation, antibiotics, and other vaccines. Drawing conclusions about the pre-vaccine mortality landscape from such a late period, the authors argue, is unsuitable for estimating how much measles immune amnesia contributed to childhood deaths in earlier centuries, when the infectious disease environment was fundamentally different.

The commentary also points to a mismatch between the timing of measles infections and the timing of childhood deaths in historical populations. In early twentieth-century Copenhagen, census data show that childhood mortality was heavily concentrated in the first year of life. Yet the average age of measles infection in the city between 1907 and 1930, estimated from weekly case records, was 5.65 years. If immune amnesia were a dominant driver of childhood infectious disease mortality, one would expect deaths from other infections to cluster in the years following the typical age of measles infection. Instead, the age distribution of deaths from causes such as infant diarrhea and whooping cough barely overlaps with the distribution of measles cases, making it unlikely that immune amnesia was a major contributor to infectious disease mortality in historic Copenhagen.

The authors examined an annual report on epidemic diseases from Copenhagen in 1911, which breaks down deaths by cause and age group. Of 917 total deaths recorded, infant diarrhea accounted for 309, nearly all in infants under one year, while whooping cough killed 176, again concentrated in the youngest children. Measles itself caused 40 deaths. When the researchers fitted gamma and power-law functions to the age distributions of measles infections and non-measles deaths, the resulting curves showed little overlap, mirroring patterns produced by earlier simulation studies. The authors caution that more research at the individual level is needed to fully understand immune amnesia’s role in the pre-vaccine infectious disease landscape, but the population-level patterns raise doubts about sweeping claims.

Historical data, the commentary argues, offers a unique set of advantages for studying how measles reshapes the immune system. Countries such as Denmark and Switzerland preserve individual-level mortality and morbidity records from long before the first measles vaccine was introduced, from an era when infectious disease mortality was still high. Because measles is so transmissible, infection was nearly universal among people who survived childhood, which means infected cohorts are highly representative of the general population, even though the disease’s ubiquity makes it impossible to construct a control group of unexposed individuals. Still, the timing of historical outbreaks has been well documented through demographic research, allowing study designs analogous to modern cohort studies to be reconstructed for past populations. Detailed case and hospital records in the archives can even be linked to death certificates, enabling individual-level analyses of long-term consequences.

Studying the pre-vaccine era also decouples the analysis from a separate and contested theory known as non-specific vaccine effects, which holds that live attenuated vaccines provide broad immune benefits that reduce all-cause mortality in vaccinated individuals. Although the theory is not widely accepted, it exists as an alternative explanation for the observed correlation between measles vaccination and reduced mortality. By examining the association between measles infection and non-measles mortality in periods when no measles vaccine existed, researchers can more confidently attribute any effect to the virus’s immune suppression rather than to beneficial vaccine side effects.

The commentary highlights international efforts to make such research feasible, including the COST Action known as The Great Leap, which works to make individual-level cause-specific mortality data available for historical populations and to harmonize historical causes of death across countries and time periods. Such infrastructure is important because contemporary data alone are often insufficient to understand the long-term consequences of infectious diseases. Even studies directly comparing vaccinated and unvaccinated children suffer from substantial confounding, since the two groups may differ systematically in socioeconomic status, healthcare access, health-seeking behavior, and parental attitudes toward medicine.

The authors advocate for a systematic integration of historical demographic and epidemiological data into research on the long-term consequences of infectious diseases, using measles-induced immune amnesia as a case in point. Linking individual-level historical infection records with cause-specific mortality data could overcome the limitations of modern studies and open new avenues for investigating how infections shape health long after the acute illness has passed. With recent global outbreaks suggesting that the World Health Organization’s goal of measles elimination by 2030 is unlikely to be met, and with vaccine hesitancy causing measles to reemerge in countries that had previously eliminated it, understanding the full cost of the virus has never been more urgent. Unlocking the archives, the authors conclude, may fundamentally expand our ability to grasp how infectious diseases continue to claim lives well beyond the moment of infection.

Subject of Research: The use of historical demographic and epidemiological records to study the long-term effects of measles-induced immune amnesia on childhood infectious disease mortality

Article Title: Why historical data matter for understanding the long-term effects of measles

Article References: Bendel, H., & Matthes, K. L. (2026). Why historical data matter for understanding the long-term effects of measles. International Journal of Public Health, 71, Article 1610290. https://doi.org/10.3389/ijph.2026.1610290

Image Credits: AI Generated

DOI: 10.3389/ijph.2026.1610290

Keywords: measles, immune amnesia, historical demography, historical epidemiology, child mortality, vaccination, infectious disease, Copenhagen, non-specific vaccine effects, public health, pre-vaccine era, mortality data