Why is measles so contagious?

Measles has R0 = 12-18 — one of the highest of any pathogen. It spreads through airborne droplet nuclei remaining infectious for 2 hours. Patients are contagious for 4 days before the rash appears — before anyone knows they are infected.

What complications does measles cause?

Complications in ~30% of cases: otitis media, severe diarrhoea, pneumonia (leading cause of measles death), encephalitis (1 in 1,000) and Subacute Sclerosing Panencephalitis (fatal, years later). Vitamin A deficiency dramatically increases severity.

What is measles immune amnesia?

Mina et al. (Science 2019, PMID 31672867) showed measles destroys 20-70% of pre-existing antibody repertoire. This "immune amnesia" lasts 2-3 years and explains why measles vaccination reduces all-cause child mortality far beyond measles deaths alone.

Why is measles resurging?

COVID-19 disruptions caused 40 million children to miss measles doses in 2021. Vaccine hesitancy and conflict-related disruption compound the problem. Susceptibility pockets accumulate until a spark ignites a major outbreak.

How many vaccine doses are needed?

Two MMR doses — first at 9-12 months, second at 15-18 months — provide >97% protection. Both are essential: the first fails to immunise approximately 5% of recipients.

What is the 95% herd immunity threshold?

Because measles R0 = 12-18, 92-95% of a population must be immune to protect unvaccinated individuals. Below this threshold, outbreaks occur in susceptible clusters including those with medical contraindications and infants too young for vaccination.

Can measles be eliminated globally?

Yes — elimination has been certified in several WHO regions. Humans are the only reservoir; the vaccine is highly effective. Barriers are programmatic: sustaining >95% coverage in every community worldwide and responding rapidly to outbreaks.

SSPE is a rare, uniformly fatal neurodegenerative disease from persistent measles virus — presenting 7-10 years after measles with intellectual deterioration, seizures and death. Occurs in approximately 1 in 10,000-100,000 cases; highest risk if measles before age 2. Entirely prevented by vaccination.

What is the role of vitamin A?

Vitamin A deficiency severely impairs measles immunity. WHO recommends high-dose vitamin A (100,000-200,000 IU by age) for all measles cases in LMICs — reducing mortality by ~50% in deficient populations.

What happened in 2022?

An estimated 9 million measles cases and 136,000 deaths occurred in 2022 — driven by the accumulation of missed doses during COVID-19 disruptions. 40 million children missed doses in 2021 alone — the worst decline in 30 years.

What is the Measles and Rubella Initiative?

The M&RI — WHO, UNICEF, CDC, American Red Cross and UN Foundation — coordinates global measles elimination strategy, funding and catch-up campaign support.

How does GMJ News cover measles?

GMJ News tracks WHO/CDC measles burden data, European outbreak alerts and vaccination coverage gaps. Measles resurgence in the WHO European region is directly relevant to Georgia's public health programme and PHIG's immunisation advocacy.

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Measles

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Measles is one of the world's most contagious infectious diseases — requiring 95% vaccination coverage for herd immunity — yet entirely vaccine-preventable with a two-dose regimen costing under US$1 (WHO). After decades of decline, measles has resurged: an estimated 9 million cases and 136,000 deaths occurred in 2022, driven by COVID-19 disruptions that left 40 million children under-immunised in 2021 alone. Measles resurgence is the clearest signal that immunisation systems need urgent reinvestment.

Key messages

Most contagious pathogen

Measles R0 of 12-18 makes it one of the most infectious pathogens known. A single case can infect up to 18 susceptible contacts; the virus remains airborne for 2 hours after an infected person leaves.

Vaccine-preventable, resurging

9 million cases and 136,000 deaths in 2022 — driven by COVID-19 disruptions that left 40 million children under-immunised in 2021. Measles resurgence is the clearest signal that immunisation systems need reinvestment.

95% threshold

Herd immunity against measles requires 95% vaccination coverage — higher than almost any other vaccine-preventable disease. Coverage below this allows outbreaks in unvaccinated pockets.

Immune amnesia

Measles destroys 20-70% of pre-existing antibody repertoire (Mina et al., Science 2019) — increasing susceptibility to other infections for 2-3 years. This explains why measles vaccination reduces all-cause child mortality, not just measles deaths.

Two-dose schedule

Two doses of MMR — first at 9-12 months, second at 15-18 months — provide >97% protection. Both doses are essential; the first fails ~5% of recipients.

Elimination achievable

Measles has been eliminated in several WHO regions. Sustained >95% two-dose coverage, strong surveillance and rapid outbreak response are the required components.

Key statistics

measles cases (2022)

WHO/CDC

136K

measles deaths (2022)

WHO/CDC

40M

children missed doses (2021)

WHO/UNICEF

95%

vaccination coverage needed

WHO

12-18

R0 of measles

CDC/WHO

2hr

virus infectious in air after patient leaves

WHO

Estimated measles deaths globally (thousands) 2000-2022 — WHO/CDC

Source: WHO and CDC. Major decline 2000-2016; resurgence 2017-2019; COVID-19 setback from 2021.

Glossary of key terms

R0
EpidemiologyBasic reproduction number — measles R0 of 12-18 is among the highest known. Herd immunity threshold = 1-(1/R0) = ~92-95%.

MMR vaccine
WHO/SAGELive attenuated Measles-Mumps-Rubella vaccine. Two doses provide >97% measles protection. First at 9-12 months; second at 15-18 months.

Immune amnesia
Mina et al. 2019Measles destroys 20-70% of pre-existing antibody memory — confirmed by VirScan profiling. Increases susceptibility to other infections for 2-3 years post-measles.

SSPE
WHOSubacute Sclerosing Panencephalitis — rare, uniformly fatal degenerative brain disease from persistent measles virus years after infection. Entirely prevented by vaccination.

Koplik spots
ClinicalPathognomonic white spots on the buccal mucosa — appear 2-3 days before the measles rash, enabling early clinical diagnosis.

Measles elimination
WHOInterruption of endemic measles transmission. Certified eliminated in several WHO regions. Requires sustained >95% two-dose coverage, strong surveillance and rapid outbreak response.