Measles: The Most Contagious Virus

What is Measles?

Measles (rubeola) is a highly contagious viral disease caused by the measles virus, a member of the Paramyxoviridae family. It's spread through respiratory droplets and aerosols and is so contagious that if one person has it, up to 90% of unvaccinated people nearby will become infected.

The basic reproduction number (R₀) of measles is 12-18, meaning each infected person spreads it to 12-18 others on average.[1] For comparison, COVID-19's original strain had an R₀ of 2-3. Measles is the benchmark for extreme contagiousness.

A History of Devastation

Measles has plagued humanity for over 1,000 years, likely evolving from a cattle virus (rinderpest). Before vaccination, it was a universal childhood disease; virtually everyone got measles before age 15.

For most children in developed countries, measles was unpleasant but survivable. But complications were common and sometimes devastating:

• Ear infections: In ~10% of cases; can cause hearing loss
• Pneumonia: Leading cause of measles death
• Encephalitis: Brain inflammation; occurs in ~1/1,000 cases; can cause permanent brain damage
• SSPE: Subacute sclerosing panencephalitis, always fatal; develops years after infection

In developing countries with malnutrition and limited healthcare, measles was catastrophic. Before the vaccine, measles killed an estimated 2.6 million children annually.

Immune Amnesia

One of measles' most sinister features is immune amnesia. The virus doesn't just cause acute illness; it wipes out 20-70% of the body's immune memory cells.

This means children who recover from measles lose protection against diseases they were previously immune to. Their immune systems must essentially be rebuilt. Studies show increased susceptibility to other infections for 2-3 years after measles.[2]

"Measles vaccination isn't just protecting against measles. It's preserving immunity to every other infection the child has fought off."

The Vaccine: John Enders and the Edmonston Strain

The measles vaccine is one of medicine's great achievements. Its development began with the work of John Enders, who won the 1954 Nobel Prize for growing poliovirus in cell culture, a technique that revolutionized vaccinology.

In 1954, Enders and colleague Thomas Peebles isolated measles virus from a 13-year-old named David Edmonston (the strain became known as the Edmonston strain). They attenuated the virus through repeated passage in cell culture, weakening it until it caused immunity without disease.[3]

The first measles vaccine was licensed in 1963. Maurice Hilleman at Merck further attenuated the strain, creating the vaccine used globally today. Combined with mumps and rubella vaccines, it became the MMR vaccine in 1971.

From Endemic to Near Elimination

Widespread vaccination transformed measles from a universal childhood disease to a rare one:

• Pre-vaccine US (early 1960s): 3-4 million cases, 400-500 deaths annually
• 2000: Measles declared eliminated from the US
• Globally: Measles deaths declined 74% between 2000-2019

Elimination means no sustained transmission; cases still occur from importation but don't spread widely. Achieving elimination requires ~95% vaccine coverage because of measles' extreme contagiousness.

The Wakefield Fraud and Its Consequences

In 1998, British physician Andrew Wakefield published a fraudulent paper in The Lancet claiming the MMR vaccine caused autism. The paper was eventually retracted, and Wakefield lost his medical license for ethical violations and data manipulation.[5]

But the damage was done. Vaccine coverage dropped in the UK and other countries. Measles outbreaks followed. The anti-vaccine movement, amplified by the internet and social media, continues to spread misinformation.

Decades of research involving millions of children have found no link between MMR and autism. But the myth persists, and children continue to die from a preventable disease.

The Current Crisis

After decades of progress, measles is resurging:

• Global cases: Rose 18% in 2022; 9 million cases estimated
• Deaths: 136,000 in 2022, mostly children under 5[4]
• Vaccine coverage: First-dose coverage dropped to 83% globally (target: 95%)
• Outbreaks: Major outbreaks in US, Europe, Africa, Asia in 2024

COVID-19 disrupted vaccination programs, leaving millions of children unprotected. Combined with vaccine hesitancy, this creates conditions for explosive outbreaks.

What's Needed

Measles could theoretically be eradicated: it infects only humans and has an excellent vaccine. But this requires:

• 95%+ coverage: Maintaining high vaccination rates everywhere
• Strengthened health systems: Reaching every child with routine immunization
• Combating misinformation: Building vaccine confidence
• Outbreak response: Rapid vaccination campaigns when cases appear

Every measles death is preventable. The tools exist. The question is whether we have the will to use them.