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# Ontario measles outbreak of 2377 cases contributed to Canada losing elimination status
- URL: https://www.coios.me/ontario-measles-outbreak-of-2377-cases-contributed-to/
- Published: 2026-10-31T11:16:56.000Z
- Updated: 2026-11-01T07:06:40.000Z
- Description: Ontario's 2377-case measles outbreak mainly affected unvaccinated young people; its strain was detected in the USA, Mexico and the Netherlands.
- Author: Daniel Ryan
- Tags: Behavioural science, Infection and pandemics, Canada, #peer-reviewed, #new, #item, #source-2026-10, #score-78

This descriptive cohort study covered 2377 measles cases reported to Ontario's surveillance system from October 2024 to October 2025\. Cases met an outbreak definition combining epidemiological, clinical, laboratory and viral sequencing criteria. Most cases (90.3%) were in historically under-vaccinated communities; 73.0% were aged 19 or under and 89.2% were unvaccinated. There were 166 hospital admissions (7%), 13 ICU admissions, 51 infections in pregnancy, 10 congenital infections and one infant death. Sequencing of the N450 genotyping region found a previously unseen variant, later detected in the USA, Mexico and the Netherlands. The analysis is descriptive only, and vaccination status was unknown for 4.1% of cases.

*Why it is interesting: Measles became re-established in a country that had achieved elimination, with transmission concentrated in under-vaccinated communities. Viral sequencing traced the outbreak strain to several other countries, and WHO gave it a formal reference name, MVs/Ontario.CAN/47.24.*

Source

[BMJ, 28 October 2026](https://doi.org/10.1136/bmj-2026-101123?ref=coios.me)

Paper

Impact of a large measles outbreak associated with transmission in the Americas and Canada's loss of measles elimination status: descriptive cohort study

Authors

Wilson SE, Lim GH, Aloosh M, Chang On A, Coghill CL, Harris T et al.

DOI

10.1136/bmj-2026-101123

Type

Peer-reviewed article

Design

Descriptive cohort of outbreak surveillance cases, Ontario, n=2377 over 49 weeks, Oct 2024–Oct 2025, with viral sequencing and phylogenetics

Verdict

New finding

Driver

[Infection and pandemics](https://www.coios.me/d-infectious-disease/)

Free full text

[Free to read at the publisher](https://doi.org/10.1136/bmj-2026-101123?ref=coios.me)

Attention

1 citation (Crossref) · as of 2026-11-01