The measles outbreak: a needless, painful experiment

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This article was published 18/03/2025 (588 days ago), so information in it may no longer be current.

Experiments come in two broad categories. First are the randomized control trials, or RCTs for short. Often termed the “gold standard,” this experimental variety is common in clinical drug trials, where the treatment is masked.

In other words, the treatment pill with the active ingredient and the control pill with just filler are both blue. Neither those administering the drugs nor the subjects in the two groups know who is receiving the real and who is taking the fake pill.

Another variant is the social experiment replicating the RCT, not in the lab but in society. The Manitoba Basic Income Experiment (or “mincome”) conducted in the 1970s was just a social experiment, where lower-income families were randomly allocated to various levels of basic income and their well-being compared to families randomly assigned to a control group that received no “treatment.”

Second, and less well-known, are natural experiments that exploit unplanned opportunities.

In what has become a classic study, economists used New Jersey’s increase in minimum wages in 1992 from $4.24 to $5.05 per hour to compare to unemployment levels in Pennsylvania, which held the line on pay. Using the workers in restaurants clustered on the border of the two states, they found the increase in New Jersey’s minimum wage did not reduce employment, upsetting standard economic theory, which predicts minimum wage increases lead to increased unemployment and wider poverty.

The key to a natural experiment is that the two settings, in this case, New Jersey and Pennsylvania, are “closely similar.” Experts believed the minimum wage experiment met this condition and awarded David Card the 2021 Nobel Prize in Economics in part for this study.

The measles outbreak in the U.S. is a contemporary natural experiment. Using hospital records, it is easy to track the measles outbreak and note the high correlation of increased incidence of measles in areas with lower vaccination rates. Of course, this is not an RCT, so the picture of reduced vaccination leading to increased cases emerges only after we repeat the experiment over time and space.

A notable example of the reduced vaccine rate leading to increased measles cases occurred in the U.K. in the ’90s. In 1996, vaccine coverage was 92 per cent, but by 2002, it had slipped to 84 per cent, and some areas dipped to 62 per cent due to unfounded concerns that vaccination caused autism. Measles rates increased sharply, and in 2006, it was declared endemic, meaning that it had regained its status as an ever-present disease.

As for the vaccine-autism association, the now-debunked study linking vaccines to autism resulted in the author losing his medical licence. The journal retracted the study when an investigation showed the study used fake data, had a tiny sample (12), and had no control group.

Multiple studies (some with hundreds of thousands of observations) have established no link between MMR vaccines (measles, mumps, and rubella) and autism. So why do we see reduced vaccination driving the current outbreak?

Specifically, why do some parents not vaccinate their children? We must always start this conversation with the presumption that all parents want to ensure the safety of their children. They love their children no less than those who follow the recommended vaccination schedule.

It is easy to finger a small cadre of anti-vax advocates pushing a variety of stories and conjectures about vaccine harms through TikTok and YouTube. However, vaccine hesitancy is not new.

In 1796, Edward Jenner scratched a lesion of a milkmaid. He injected the material (pus) into an eight-year-old and then exposed the boy to smallpox, a highly infectious disease. The child remained healthy, proving that this technique was an effective vaccine. Ignore the fact that this experiment would never receive ethical approval now.

So-called “anti-vaxxers” who mobilized in response to Jenner’s experiment raised various objections. These included the use of animal products to intervene in God’s will and the fear that injecting material from a cow would cause the recipient to develop bovine features. Others objected to science displacing religious practices such as faith healing and exorcisms.

A common refrain among the modern antivax movement is that the harms associated with the vaccine are more significant than reported. Conspiracy variants of this position argue that Big Pharma covers up the side effects of vaccines.

Take measles as an example. A common side effect of vaccination is a mild fever resulting from the creation of an immune response. This occurs in about 20 per cent of children vaccinated. However, measles produces a much more intense fever in 100 per cent of affected children. This disease-induced fever produces serious outcomes and even death in a small number of those who fall ill. Equally important is that measles impairs the immunity against all illnesses for weeks, months or even years for an unlucky few.

The MMR vaccine is 97 per cent effective against measles. Because measles is one of the most contagious diseases, disease incidence rises when coverage falls to under 90 per cent. In 2000, it was on the cusp of eradication (along with polio), but the recent rise in cases for both diseases has set that back,

But fundamentally, the current vaccine hesitancy derives from the fact that vaccines have succeeded. Modern parents have no experience with the scourge and suffering caused by measles, mumps, rubella, pertussis, polio, and diphtheria. We have become “disease naïve,” and we need to relearn the lessons of the past the hard way.

Gregory Mason is an associate professor of economics at the University of Manitoba.