Measles in the United States: Should We Worry?

Paul G. Auwaerter, MD


February 06, 2023

This transcript has been edited for clarity.

Hello. This is Paul Auwaerter with Medscape Infectious Diseases, speaking from Johns Hopkins University School of Medicine. Why might I pick the topic of measles? Why should we worry about this, especially when we still have subvariants of Omicron circulating, large amounts of early influenza, respiratory syncytial virus, and even avian influenza, which, unfortunately, has led to millions of chickens being culled in Nebraska over this past week?

I thought I'd give a bit of a personal perspective. As an infectious disease fellow 30 years ago, I wanted to study virology and immunology. At the time, even though HIV had vast importance, I was a bit of a contrarian and worked in the lab of Dr Diane Griffin at Johns Hopkins.

The reason I thought this was an interesting intersection is that at the turn of the 19th to the 20th century, an Austrian pediatrician and scientist by the name of Clemens von Pirquet became famous for a couple of things. One was for coining the word "allergy" to explain hypersensitivity to horse serum and similar instances. He also laid the foundation for tuberculin as part of the Mantoux test, otherwise now known as the purified protein derivative skin testing for TB.

He made the interesting observation in his patients with TB and positive skin responses that, following measles, those skin responses vanished, suggesting that the infection of measles caused an immune suppressive illness.

Indeed, this is something that was really the first virus — subsequently identified as a virus by John Enders many decades later — and that this was the first instance of an immunosuppressive virus long before HIV. Although there was a successful, attenuated measles vaccine that had become a component of MMR that was 97% effective after two doses, and even though measles was vastly reduced in the United States, it remained a significant problem in Africa and countries of low resources, with infants and young children dying after measles, especially after postinfectious illnesses such as pneumonia. Although measles was declared eradicated in the United States in 2000, there have been continued outbreaks from time to time.

The focus was really the fact that measles vaccine, even though widely successful, could only really engender good vaccine responses in children 12 months or older. The idea was to find a safe and effective vaccine in infants less than a month old, so the task was to understand whether something could be developed safely at that time that might not need to be refrigerated, which, of course, was a big deal to maintain a cold chain, especially in countries with underimmunized children.

Many of you are already aware that you need more than approximately 95% compliance to really achieve effective herd immunity. That had been the case — or nearly so — in the United States for quite a while.

With the pandemic, there have been vast disruptions in routine immunizations, both because of not getting healthcare visits and a large amount of negativity about vaccines, which, of course, has been building ever since the Wakefield episode, linking it to autism without any clear basis of fact; and also, of course, more recently with issues regarding SARS-CoV-2 immunization, especially in children.

Recently, the CDC and the WHO have declared a vast problem of over 40 million people who have missed recommended measles vaccines, with only 71% of populations receiving two doses. They've labeled this as a growing threat and a growing number of dangerously susceptible children.

By way of context, it's useful to remember what happened in 2014 and 2015 with measles, having many cases in the United States, and the outbreak, especially in Disneyland, where although the index patient was unknown, the strain of measles was similar to what had been circulating in the Philippines. There were 129 measles cases, including among 55% of people who had some degree of immunization, and over 20% of those 129 people required hospitalization.

This is just one instance showing that if there are indeed problems not only in the United States but also elsewhere, suddenly there could be a case for yet another worry about viruses that could be quite preventable. Vaccine is highly effective, but it's really in the context of that herd immunity. Anytime you have many cases — and this is true in the Disneyland instance — it's not fully protective from infection anymore, although it may help avoid severe infection.

The idea really is to help take preventive measures, and of course, reinforce efforts not only here in the United States but also worldwide. Again, 30 years ago, I made the estimation that measles really didn't have the legs for a long-lived career and pivoted elsewhere. As a reminder, in the prevaccine era, there were 500 deaths per year in the 1950s and 1960s; 48,000 hospitalizations; and 1000 bouts of encephalitis for more than nearly half a million infections.

Of course, we won't quite get back to that era, but it is something that can cause vast disruptions. I think all of us would like to get back to normalcy, so understanding the benefits of vaccines in the context of dangers is as important as ever.

Certainly, if any of your patients are hesitant about getting routine vaccines, it's hard to bring them because many of them are steadfast in their efforts. This is something that hopefully we won't come to see, but we should be prepared because many of us, including myself, have never seen a case of measles in the United States.

I hope that's some food for thought, and some background and history that might be helpful as well. Thanks so much for listening.

Paul G. Auwaerter, MD, is a professor of medicine at Johns Hopkins University School of Medicine and clinical director in the Division of Infectious Diseases at Johns Hopkins Hospital in Baltimore, Maryland. He is an editorial advisor and hosts the Auwaerter on Infectious Diseases series on Medscape.

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