What is the best way to eliminate measles?

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CLINICAL MATTERS

In the year 2000, the US Centers for Disease Control and Prevention (US CDC) declared that measles in the US had been eliminated. This meant that there was no continuous spread of measles in that country for more than twelve months. Sporadic cases from imported infections have occurred since then but have not caused widespread outbreaks due to high rates of vaccination. In fact, the vast majority of localized measles outbreaks with some limited spread have been seen in communities with low vaccination rates. Last month, the US CDC reported a death from measles in an unvaccinated child in Texas. This was the first measles fatality in the US since 2015. Aside from this death, 159 cases of measles have been reported in the outbreak area with 22 of these patients needing to be hospitalized at the time of this writing. Over half of the cases are not vaccinated, while 74 are of unknown vaccine status and only five are known to have gotten at least one measles vaccine dose.

Measles elimination is a historic milestone for any country because measles is one of the most contagious diseases in the world. During the pandemic, scientists were very concerned with the unchecked spread of Covid-19, which had an estimated reproductive number (R₀) of two to 2.5. In comparison, measles has an R₀ which is at least six times higher than Covid-19, ranging from 12 to 18. This means that for every one case of measles, 12 to 18 people get infected and each of those cases can then infect that number of susceptible hosts and so on. Measles spreads by respiratory aerosol, and an infected person will infect 90 percent of non-immune people with whom he or she come into close contact. Immunity can be achieved by previous infection or measles vaccination.

Before the discovery of the measles vaccine, millions of measles deaths occurred every year, mostly among children under the age of five. One in five people who contract measles will end up hospitalized and up to three in one thousand cases will die. The death rate is much higher in malnourished and immunocompromised populations, where up to 30 percent of people who develop measles pneumonia die. Subacute sclerosing panencephalitis or SSPE is another deadly complication of measles. SSPE involves a progressive inflammation of the brain which is almost always fatal and can occur years after the initial measles infection. SSPE is seen in about one in one thousand infections, especially among unvaccinated infants under 15 months of age. Among those who survive a measles infection, antibody production and the immune response are substantially impaired for months, making them more susceptible to other infections including those that cause deadly bacterial pneumonia.

The discovery of the measles vaccine in 1957 and its subsequent rollout has decreased the number of incident measles cases in the US by 97 percent. The vaccine is a live, weakened virus which is 95 percent effective in preventing measles in those 12 months and older after one dose, and 99 percent effective if two doses are given. Because measles is so contagious, elimination is possible only if 95 percent of a population is immune, either through vaccination or natural infection. This phenomenon is known as herd immunity and measles has the highest threshold compared to other vaccine preventable diseases due to its extreme transmissibility. If immunity dips below the 95 percent threshold, outbreaks are expected to occur and recur until herd immunity is restored. Measles outbreaks are the first outbreaks to occur among vaccine-preventable diseases, it serves as an early warning system that vaccine coverage is dropping. The current outbreak and rare measles death in the US is a harbinger of more outbreaks of vaccine-preventable diseases to come unless there is a timely intervention to restore vaccine-induced disease immunity.

What about closer to home? Measles outbreaks in the Philippines are unfortunately not unusual, and hundreds of unvaccinated Filipino children continue to succumb to measles every year despite the availability of the measles vaccine. From the peak vaccination years during DOH Secretary Juan Flavier’s tenure when vaccination programs were very popular and vaccines were being given even in fast food restaurants, vaccine confidence and uptake have gradually decreased over the years due to a number of factors. Increasing vaccine misinformation and disinformation, lack of budget, and increasing apathy have brought the vaccination rates below the herd immunity threshold. When the Dengvaxia controversy occurred, vaccination rates cratered and there were subsequent outbreaks of measles, chicken pox and even polio. Measles outbreaks are particularly deadly in a developing country setting due to the increased mortality that occurs in malnourished children. Outbreaks in countries like the United States tend to be less deadly due to better healthcare and nutrition, but going by the same thought process, properly following science-based policies should be stronger as well and there is no reason why measles outbreaks should occur.

So how do we stop a measles outbreak? Good medical care and the use of vitamin A can help patients recover. Infection control measures including quarantine and isolation are important. However, the mainstay of eliminating a measles outbreak hinges on an aggressive measles vaccine campaign to deny the virus new hosts. A strategy known as “ring vaccination” focuses on rapidly restoring measles immunity above the 95 percent threshold in the locations adjacent to the outbreak area. This involves a rigorous information dissemination and vaccination program in partnership with the local governments and the private sector. Most recently there was a measles outbreak in BARRM and this whole-of-society approach eventually worked, but it took several months to get it under control. 

One unique challenge the US is facing with their measles outbreak is that the new Department of Human and Health Services Secretary was formerly a leading figure in anti-vaxxer circles. Robert F. Kennedy Jr. expressed skepticism of vaccine safety and promoted discredited information linking vaccines to autism. He has quoted falsely inflated figures on the frequency of adverse reactions to routine vaccination. Most recently, he wrote an Op-Ed in which he did acknowledge that vaccination was needed to eliminate the current measles outbreak. While critics said that he did not push vaccination aggressively enough in the face of a public health emergency, many of us were stunned that he would even endorse and acknowledge that vaccines were safe and effective to begin with. For me, this is a start and while it isn’t ideal, it is something that medical societies and public health authorities can begin to work with to address this ongoing outbreak.

The measles vaccine has saved over 94 million lives in the last 50 years. It has been proven to be safe, with serious reactions occurring in less than one in one million recipients. This is thousands of times safer than achieving immunity through natural infection. These are the facts. It is a shame and a tragedy that people have to die needlessly because of false information. If the US doesn’t get its act together, many other vaccine preventable diseases will make a comeback and kill more people.