How does the measles vaccine work and why do outbreaks still happen?

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1. 1

   Measles vaccine (Wikipedia)

   WikipediaPublished Oct 6, 2026Checked Oct 10, 2026

   “Measles vaccine is a live attenuated vaccine that protects against becoming infected with measles. Nearly all of those who do not develop immunity after a single dose develop it after a second dose. When the rate of vaccination within a population is greater than 92%, outbreaks of measles typically no longer occur; however, they may occur again if the rate of vaccination decreases. The vaccine's effectiveness lasts many years. It is unclear if it becomes less effective over time. The vaccine may also protect against measles if given within a couple of days after exposure to measles. Measles is a highly contagious viral illness that can lead to serious complications, including pneumonia, acute encephalitis, and, in rare cases, long‑term neurological disease. Pregnant women are at increased risk of severe respiratory complications and adverse pregnancy outcomes such as pregnancy loss and premature birth. The vaccine is generally safe, even for those infected by HIV. Most children do not experience any side effects; those that do occur are usually mild (such as fever, rash, pain at the site of injection, and joint stiffness) and short-lived.”

2. 2

   MMR vaccine (Wikipedia)

   WikipediaPublished Oct 6, 2026Checked Oct 10, 2026

   “The MMR vaccine (abbreviated as MMR) is a combination vaccine against measles, mumps, and rubella (German measles). It contains the combined measles vaccine, mumps vaccine, and rubella vaccine into a single injection. After two doses, 97% of people are protected against measles, 88% against mumps, and at least 97% against rubella. The vaccine is also recommended for those who do not have evidence of immunity, those with well-controlled HIV/AIDS, and within 72 hours of exposure to measles among those who are incompletely immunized. It is given by injection. Measles is a highly contagious viral illness that can lead to serious complications, including pneumonia, acute encephalitis, and, in rare cases, long‑term neurological disease. Pregnant women are at increased risk of severe respiratory complications and adverse pregnancy outcomes such as pregnancy loss and premature birth. The MMR vaccine is widely used around the world. As of 2012, 575 million doses had been administered since the vaccine's introduction worldwide. Measles resulted in 2.6 million deaths per year before immunization became common.”

3. 3

   Measles and Rubella Elimination Trends in the WHO Eastern Mediterranean Region, 2023-2024: Progress and Recent Epidemiological Shifts.

   Vaccines (Farid et al.)Published Jul 27, 2026Checked Oct 10, 2026

   “Regional measles incidence increased from 110.8 to 116.3 per million population, while rubella incidence more than doubled from 1.9 to 4.3 per million. Large outbreaks in Yemen, Iraq, and Afghanistan disproportionally drove regional trends. MCV1 coverage remained stable at approximately 80%, while MCV2 coverage increased marginally from 73% to 75%. Only nine of 22 countries achieved ≥95% coverage for both doses in 2024. Persistent zero-dose populations, high dropout rates, and ongoing immunity gaps sustained transmission across multiple settings. The EMR remains off track to achieve measles and rubella elimination by 2030. Accelerated, equity-focused efforts are urgently needed to strengthen routine immunization systems, reduce zero-dose population, enhance surveillance capacity, and improve outbreak response-particularly in fragile and conflicted-affected settings.”

4. 4

   Lessons for Immunisation Policy and Practice From the Deadly Measles Resurgence in Bangladesh.

   Tropical medicine & international health : TM & IH (Haque et al.)Published Jun 25, 2026Checked Oct 10, 2026

   “Bangladesh is experiencing one of the deadliest outbreaks of measles in 2026, with at least 472 suspected child deaths and over 67,079 suspected cases as of 27 May 2026. It has happened primarily following a fall in measles vaccination coverage in 2025, largely due to the cancellation of a planned 2024 Measles-Rubella vaccination Campaign and major political unrest. This editorial, based on available surveillance data, disease transmission modelling and lower vaccination coverage, argues that the 2026 measles outbreak was predictable, preventable and needed prompt action and management. We urge attention to addressing the issues related to structural and programmatic barriers, political and financial gaps in the planning, challenges related to Supplementary Immunisation Activity (SIA) scheduling and recommended-to protect vulnerable high-risk communities.”

5. 5

   Risk and Spatial Spread of a Measles Outbreak in Texas.

   Viruses (Ndeffo-Mbah et al.)Published Jun 4, 2026Checked Oct 10, 2026

   “However, investigations into the geographic spread of this outbreak remain limited. We developed a measles transmission model parameterized with 2020-2024 measles-mumps-rubella (MMR) vaccination coverage and human mobility data in Texas. We conducted sensitivity analyses to evaluate how variation in model parameters affects outcomes. We compared model predictions to data from the 2025 measles outbreak and simulated scenarios for outbreak originating in different low vaccination counties. We found that an outbreak originating in Gaines County would have at least 80% probability of directly generating local outbreaks in eight neighboring counties in West Texas. The spatial spread was highly sensitive to the basic reproduction number (R0) and population-level MMR vaccination coverage. Outbreaks originating in counties with low MMR vaccination rates, such as Polk, Montague, or Limestone County, are likely to spread to large metropolitan areas such as Houston and Dallas. Measles has the potential to cause statewide outbreaks in Texas. Our modeling framework can inform county-level risk assessment and guide preemptive vaccination strategies.”

6. 6

   Serological Protection After Routine Measles-Containing Vaccination Among Children Aged 1-5 Years in Low- and Middle-Income Countries: A Systematic Review.

   Vaccines (Hussain et al.)Published Aug 31, 2026Checked Oct 10, 2026

   “Eighteen studies met the eligibility. These studies were from 14 LMICs across four WHO regions (61.1% African Region, 27.8% Eastern Mediterranean Region, 5.6% each South-East Asia and the region of the Americas). Reported MCV seroprotection following completion of the two-dose schedule generally ranged from 30.6% to 100%, with the highest levels (87-100%), but with evident lower protection in specific settings, such as rural Pakistan (30.6%) and Ethiopia (40-54%) despite having documented vaccination records. Lower protection was consistently associated with undernutrition, human immunodeficiency virus (HIV) infection, incomplete or delayed vaccination, younger age at first dose, and weak programme performance. Routine two-dose measles vaccination generally provides substantial serological protection among children aged 1-5 years in LMICs. Nevertheless, methodological heterogeneity and geographical evidence gaps limit direct comparisons and reduce confidence in cross-study interpretation.”