The Ninety-Five Line
Measles is the most contagious virus we routinely vaccinate against. Stopping it takes near-total immunity. The world has been stuck short of that line for fifteen years, and the gap is now showing up as outbreaks.
Two-dose coverage WHO says each community needs to stop measles circulating. Global first-dose coverage in 2024: 84%.
One case can infect a dozen or more
The basic reproduction number (R₀) is how many people one case infects in a fully susceptible population. The higher it is, the more of a community has to be immune to stop spread: roughly 1 − 1/R₀.
At R₀ 12–18, measles needs higher immunity than any other disease on this chart. One dose of MMR is about 93% effective and two doses about 97%, which is why the target is 95% coverage with both doses.
The virus can linger in a room's air for up to two hours after an infected person leaves, and infects up to 9 in 10 unprotected close contacts.
R₀ values are typical textbook ranges (Anderson & May; CDC/WHO). Real-world R₀ varies with setting and population density. Thresholds are calculated as 1 − 1/R₀.
Most of the world sits below the line
Vaccination coverage on one scale from 50% to 100%. The dashed red mark is the 95% target.
countries, dose 1 (2024)
(2024)
(2024–25 school year)
Sources: WHO/UNICEF WUENIC 2024; Population Medicine LMIC analysis (2025); CDC kindergarten vaccination survey 2024–25 (exemptions hit a record 3.6%).
A decade of gains, then fifteen years flat
Global first-dose coverage climbed 12 points in the 2000s, stalled at 84–86% through the 2010s, dipped during COVID-19, and has only partly recovered.
WHO/UNICEF estimates (WUENIC), via CDC MMWR "Progress Toward Measles Elimination" series. Only reported years are plotted; lines connect them.
Deaths fell 88%. Cases are climbing again.
Since 2000 the vaccine has saved about 59 million lives. But in 2024 there were more infections than before the pandemic, and outbreaks in more countries.
Immune amnesia. In unvaccinated children, measles wiped out 11% to 73% of the antibodies they already had against other pathogens, leaving them open to infections they had already beaten. Mina et al., Science, 2019
North America's measles-free status is slipping
US cases in 2025 were the highest since 1992. Canada lost its elimination status in November 2025. PAHO reviews the US status in November 2026.
That is nearly eight times 2024's 285 cases. 93% of confirmed cases were unvaccinated or of unknown status, and 11% were hospitalised.
A country loses elimination status after 12 months of continuous spread of one viral lineage. Canada had held the status since 1998.
Closing the gap is a records check away
The 95% line is met or missed one family, school and clinic at a time.
Check your records
Two MMR doses are about 97% effective, for life. Adults born after 1957 with no record or blood test can still get vaccinated.
Travelling with a baby?
CDC advises infants aged 6–11 months get an early MMR dose before international travel. It doesn't count toward the usual two.
Know your school's number
Coverage is local. A state can average 93% while single schools sit far below the line, and outbreaks start there.
Measles is the canary for every other vaccine program. It's so contagious that it shows up first wherever coverage slips.