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  • Writer's pictureP.K. Peterson

Measles Is Back: Why?

“Measles is called the inequity virus for good reason. It is the disease that will find those who aren’t protected.”

Kate O’Brien, MD, director for immunization, vaccine, and biologics, World Health Organiztion

“The problem is, it doesn’t require vaccination levels to fall by half, or even by a quarter to produce outbreaks of a disease like measles, which in populations that have never been exposed to it before is many times more infectious than Covid was at first.”

David Wallace-Wells, New York Times opinion writer, February 1, 2024   


Measles is a vaccine-preventable disease that, nonetheless, kills over 130,000 people a year world-wide. Recently, there has been a substantial rise in the number of measles cases.

In November 2023, the World Health Organization (WHO) and the Centers for Disease Control and Prevention reported an increase in measles outbreaks in Europe and the U.S., respectively. (See November 16, 2023 New York Times article “Measles Cases Climb Across the Globe.) In mid-December 2023, the WHO reported the number of cases of measles had jumped from 941 in all of 2022 to 30,000 in the first 10 months of 2023. As David Wallace-Wells, opinion writer for the New York Times, stated: “This is the kind of spike—a 3,000 percent increase—that looks implausible in headlines.”

My aim in writing this week’s Germ Gems post is to refresh memories about measles and identify the basis for this alarming uptick in cases.

Recap of measles. Measles (aka rubeola) is a highly contagious, potentially fatal, but vaccine-preventable disease caused by measles virus, a single-stranded RNA virus of the genus Morbillivirus, family Paramyxoviridae. The virus is airborne, transmitted from person-to-person by coughing or sneezing.

Very few pathogens are as contagious as measles virus. It has a reproductive number (R0) between 12-18. (In comparison, the R0 for SARS-CoV-2, the cause of COVID-19, is between 1.4 and 2.4.) This means that each person with measles would, on average, infect 12-18 other people in a totally susceptible population.

Symptoms of measles include fever, maculopapular rash, and at least one of the following: cough; mucus discharge from the nose; or conjunctivitis. Measles can affect many organs including the middle ear (otitis media), lungs (pneumonia), and gastrointestinal tract (diarrhea). Neurological complications are uncommon but, when they occur, are very serious. For every 1,000 children with measles, one or two will die from it. As I pointed out in my November 17, 2019 Germ Gems post, “The Double Whammy of Measles,” measles is immunosuppressive which means it increases the susceptibility to other infections, some of which contribute to measles-related deaths.

So why the rise of measles cases since 2022? In the 1960s, a highly effective measles vaccine was developed. It’s been one of the routine childhood vaccines ever since. It is administered together with mumps and rubella vaccines as MMR at 12 to 15 months of age, and again at 4 through 6 years of age. Sadly, in recent years, the measles vaccine has been targeted by anti-vaxxers.

Ever since the advent of COVID-19 in December 2019 and associated anti-vax disinformation campaigns, public health officials have worried about carryover effects of COVID-19 anti-vax disinformation on routine childhood vaccines. Indeed, a decline in MMR vaccination, in parallel with an increase in vaccine disinformation, has played a role in the increase in measles outbreaks. And while New York Times journalist, David Wallace-Wells claims,  “[A] vast majority of people are vaccinated against diseases like measles and a vast majority of them continue to vaccinate their children against them too,” a “vast majority” may not be enough. Most experts contend that at least 95% of people in any given community need to be immune to measles for the protection of those who aren’t immune.

In the U.S., the recent increase in measles cases has hit hardest the city of Philadelphia and the state of Washington. Abroad, Kazakhstan, Krygyzstan, and Russia along with a recent vicious surge in the UK have been most seriously impacted. Fortunately, to date, the numbers of severe cases and fatalities have been fairly limited. But, we need to remember that worldwide, measles continues to kill over 130,000 people a year, with mounting death tolls in low-income countries like those in sub-Saharan Africa. It’s in these countries that the challenges of measles and measles outbreaks must be properly addressed.

Can measles be eradicated? “Elimination” is defined as the reduction to zero of the incidence of infection in a specified geographic area. Measles has been officially eliminated in 81 countries, including the U.S. “Eradication” is defined as the permanent reduction to zero of the worldwide incidence of infection. Of the thousands of viral pathogens, only two have been eradicated: the smallpox virus in humans in 1980; and rinderpest virus in cattle in 2011. Both pathogens were eradicated due to heroic vaccination programs.

Rinderpest virus, like measles virus, is a member of the Morbilliformis genus of viruses. It is, however, a pathogen of cattle, not humans. Nonetheless, the two viruses are closely related. Studies published in Science in 2020 indicate that measles virus diverged from rinderpest virus in the 6th century BCE, possibly coinciding with the rise of large cities in an environment where cattle and humans lived in close proximity. Yet, the rinderpest virus has been eradicated in cattle. So, why not the measles virus in humans?

Experts who’ve studied measles carefully also think the eradication of measles in humans is feasible due to the effectiveness of the measles vaccine. This is an ambitious yet attainable goal. But, given all the other public health priorities, the eradication of measles probably won’t be accomplished in the near future. Remember smallpox eradication essentially started in 1798 with the jeering of Edward Jenner when he introduced vaccination with material from cowpox lesions in milkmaids that cross-protected against smallpox virus infections in humans. Approximately 200 years later (1980), the WHO declared smallpox eradicated. It may be a long road until we reach the end of measles virus. But, it shouldn’t take 200 years.   

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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