Is a measles spike a bellwether for other vaccine-preventable outbreaks?

Measles cases have risen precipitously in recent months — and that could be a sign of more vaccine-preventable outbreaks to come.

“Measles is usually a harbinger of other weaknesses in immunization programs,” said Chris Gregory, senior adviser for health at UNICEF.

In recent years, routine vaccination programs have been disrupted by the COVID-19 pandemic, conflict, and displacement. And now as social distancing efforts have been lessened in many countries, people are interacting at higher rates — giving the disease opportunity to spread.

“It is felt most strongly in low-income and low-middle-income countries,” said Dr. William Perea, team lead of the World Health Organization's department for vaccine preventable diseases outbreak reduction and recovery.

Measles is one of the world’s most contagious diseases and its symptoms are obvious, whereas other diseases might infiltrate communities at a slower, more subtle pace.

“Measles is not the most subtle of things. When you get a lot of kids in the community who are developing fever and rash in a short period of time, then you're gonna know about it,” Gregory said.

“We're really cognizant that we could well be seeing outbreaks of other diseases that might develop a bit more slowly. That could occur several years later after the pandemic just because of these immunity gaps that are developing,” he added.

In January and February, cases of measles increased by nearly 80% globally compared to the same period last year, with over 17,000 cases reported as opposed to nearly 10,000. Across the African continent, measles cases rose by 400% between January and March, compared with last year.

Outbreaks strike more countries

At least 95% of children need to be immunized with the two-dose vaccine in order for countries to protect communities from measles outbreaks.

Without high vaccination rates, the world will see cycles of spikes in measles cases every few years, Gregory said, adding that “the intervals between those spikes are somewhat unpredictable and the heights of those spikes are somewhat unpredictable.”

“Measles is one of the historically largest killers of children. And when we see measles outbreaks get to a sufficient size, we're going to see, unfortunately, quite a lot of deaths,” Gregory added.

In 2019, WHO reported the highest number of measles cases since 1996 — nearly 870,000 cases worldwide. The high caseloads were driven by really large outbreaks in countries. Nearly half of the cases in 2018 were from five countries — Democratic Republic of Congo, Liberia, Madagascar, Somalia, and Ukraine.

Between 2018 and 2020, nearly 8,000 children in DRC died from it. Madagascar saw over 1,000 deaths from measles in 2019.

Ukraine also had a major outbreak due to low immunization rates. Between 2017 and 2019, the country reported 115,000 measles cases. Immunization rates have improved but “overall population immunity remains low,” according to WHO.

“Now the ongoing war is greatly increasing the risk of a measles outbreak, with so many families displaced and staying in crowded, temporary accommodation, and many others unable to access health-care services," said Dr. Jarno Habicht, WHO representative in Ukraine, in a recent press release.

Because of the major measles outbreaks, there were some levels of immunity in communities in the years that followed from children that survived the disease — social distancing efforts necessitated by COVID-19 also had an impact on the spread of infectious diseases overall. But since then, enough unvaccinated children have accumulated to spur another round of large-scale outbreaks, Perea said.

In 2020, the coverage of the first dose of the measles vaccine dropped to 84% from 86% the year before — while that might seem small, it is a drop of 3 million children and is the lowest level of coverage since 2010, he said. Official data from 2021 is not yet available.

“For many other diseases, the impact of these disruptions to immunization services will be felt for decades to come,” Dr. Tedros Adhanom Ghebreyesus, WHO’s director-general, said in a press release.

While the global spike this year hasn’t been as high, of concern is that measles outbreaks are spread across a broader range of countries than in 2019, Gregory said.

The challenge is having so many countries respond on the scale that’s needed, in a timely manner, he said. At the onset of outbreaks, measles responses are localized, working to stop it from spreading in that community and then to other communities.

“This increase that we're seeing in so many different countries makes it really hard to find the resources to support all of those countries,” Gregory said. “If it was more localized, and in a limited number of countries, then the chances of controlling it are much better.”

Twenty African countries reported measles outbreaks in the first quarter of this year, as opposed to the same period last year, where only 12 had reported cases.

Some of the other diseases resulting from failure to immunize that could take longer to emerge as outbreaks include diphtheria, meningitis, whooping cough, polio, and yellow fever.

According to WHO, this is already starting to happen.

“Twenty-four countries confirmed outbreaks of a variant of polio in 2021, which is four more than in 2020. In 2021, 13 countries reported new yellow fever outbreaks in the African region, compared to nine in 2020 and three in 2019,” the agency said in a release.

Conflict, displacement, and COVID-19

Over the past year, there have been 21 large outbreaks, and the countries with the largest burden of measles cases include Somalia, Yemen, Afghanistan, Nigeria, and Ethiopia — all countries that have at least one part of their countries in conflict and less than 70% of their children fully vaccinated, with only 46% of children in Somalia having received the first dose as of 2020.

“​​A major commonality between those countries is that there have been challenges because of the conflicts in reaching certain communities,” Gregory said.

Conflict zones often don’t have functioning health systems or adequate cold chain systems, and organizing vaccination campaigns have extra layers of complications in terms of security and cost, Gregory said. It can also be difficult to make communities aware of vaccination campaigns, and ensure their safety when they do gather.

Somalia, which tops the list, is also facing widespread drought — the worst in 40 years. The measles cases have largely been reported from drought-affected areas. Displacement fuels outbreaks, as people live in crowded displacement camps.

“Whenever there's an influx of a new population, there's a possibility that you could be introducing disease into another population which wasn't there before,” Gregory said.

Malnutrition also makes children more susceptible to measles, Perea said. “At the same time, once the measles or the other infectious diseases affect the kid, they go into the malnutrition cycle quite easily,” he said.

And despite the COVID-19 pandemic being in its third year, disruptions persist. As of the beginning of April, 19 measles vaccination campaigns globally were still postponed — putting 73 million children at risk.

And meaningful improvements in surveillance have yet to return to pre-pandemic levels, Gregory said.

“That doesn't mean that there's not as many cases out there, we just might be detecting a smaller percentage of them,” he said. “Most countries have seen a decrease in the number of specimens that are getting to the labs for testing and the number of suspected cases that are being reported.”