Measles vaccination coverage has steadily declined since the beginning of the COVID-19 pandemic, according to a report published on Nov. 23 by the World Health Organization (WHO), the United States Centers for Disease Control and Prevention (CDC) and several university researchers, including Matthew Ferrari, director of the Center for Infectious Disease Dynamics at Penn State. Specifically, in 2021, a record high of nearly 40 million children missed a measles vaccine dose, with 25 million children missing their first dose and an additional 14.7 million children missing their second dose.
The team noted that the decline is a significant setback in global progress toward achieving and maintaining measles elimination and leaves millions of children susceptible to infection.
“Measles is one of the most contagious human viruses and can be quite serious if there aren’t sufficient resources to manage symptoms,” said Ferrari, who has worked with the WHO for the last 10 years to estimate the global burden of measles cases. “In under-resourced settings, as many as 5% of children infected with measles could die, and the likelihood of severe outcomes is higher in younger kids.”
Ferrari explained that globally, measles vaccination occurs through two mechanisms — parents bringing their kids in for routine visits at health facilities and large-scale community-based campaigns that try to reach those who have poor access to health facilities.
“Both of these mechanisms were disrupted because of COVID-19,” he said. “Many children missed their scheduled opportunities for vaccination over the last three years, and now is a critical time to allocate resources to making up that vaccination gap before those communities experience large outbreaks.”
In a release, WHO Director-General Tedros Adhanom Ghebreyesus said, “The paradox of the pandemic is that while vaccines against COVID-19 were developed in record time and deployed in the largest vaccination campaign in history, routine immunization programs were badly disrupted, and millions of kids missed out on life-saving vaccinations against deadly diseases like measles. Getting immunization programs back on track is absolutely critical. Behind every statistic in this report is a child at risk of a preventable disease.”
To determine the global number of measles cases, Ferrari led the team’s development of a statistical model that integrates surveillance data collected from health facilities across the world to estimate the number of cases that likely occurred but were not recorded.
“The vast majority of measles cases occur in the community and are not recorded by health systems,” he explained.
To determine the number of measles fatalities, Ferrari co-developed a model of the case fatality rate, or the percentage of cases that result in fatalities.
“We integrated data from many studies around the world to develop a model to predict the likelihood that a case will result in a death,” said Ferrari. “By summarizing the patterns in specific places and times we were able to develop a model that could predict the case fatality rate in places and times where there were no studies.”
The modeling results revealed that an estimated 9 million cases and 128,000 deaths from measles occurred worldwide in 2021. Twenty-two countries experienced large and disruptive outbreaks, with 18 of these occurring in Africa.
The team estimated that global coverage with a first measles vaccine dose increased from 72% in 2000 to a peak of 86% in 2019 but decreased during the COVID-19 pandemic to 83% in 2020 and 81% in 2021, the lowest measles vaccine coverage recorded since 2008. In addition, only 71% of children received their second measles-containing vaccine dose in 2021.
“Most children — more than 80% — will be protected by the first dose, but those that are not have very little protection at all,” said Ferrari. “The second dose is critical for catching up those kids that weren’t protected by the first dose.”
The team noted that coverage of 95% or greater of two doses of measles vaccine is needed to create the herd immunity that would ultimately protect communities and achieve and maintain measles elimination.
“The record number of children under-immunized and susceptible to measles shows the profound damage immunization systems have sustained during the COVID-19 pandemic,” said CDC Director Dr. Rochelle P. Walensky in a release. “Measles outbreaks illustrate weaknesses in immunization programs, but public health officials can use outbreak response to identify communities at risk, understand causes of under-vaccination, and help deliver locally tailored solutions to ensure vaccinations are available to all.”