Measles outbreak traced back to Mennonite gathering, Ontario’s top doctor says

An ongoing outbreak of measles in Ontario has been traced back to a large gathering in New Brunswick last fall that was attended by guests from Mennonite communities, the province’s top doctor says.

Chief Medical Officer of Health Dr. Kieran Moore sent a memo to Ontario public health units on March 7 in which he revealed the connection to the New Brunswick gathering, particularly as it pertains to a rise in measles cases in southwestern Ontario.

• What you need to know about the spike in measles cases in Ontario

A report from Public Health Ontario last week noted that the province has seen a total of 470 cases associated with the New Brunswick outbreak between October 18 of last year and March, 19 of this year.

Public Health Ontario said that a total of 34 measles cases in the province that are associated with the New Brunswick outbreak have required hospitalization, including two that needed treatment in intensive care.

All but two of the cases that required hospitalization were in unimmunized individuals, including 29 children.

“Over 90 per cent of cases in Ontario linked to this outbreak are among unimmunized individuals,” Moore warned in his memo. “Cases could spread in any unvaccinated community or population but are disproportionately affecting some Mennonite, Amish, and other Anabaptist communities due to a combination of under-immunization and exposure to measles in certain areas.”

The New Brunswick outbreak was declared over on Jan. 7 but Public Health Ontario has said that it continues to see new cases associated with the original outbreak.

Notably, Public Health Ontario has said that the number of cases in Ontario linked to the New Brunswick exposure increased by 120 between March 14 and March 19.

It also said that all but seven of the 440 confirmed measles case in Ontario so far this year have been “linked” to the “multi-jurisdictional outbreak” that originated in New Brunswick.

The cases have spanned across 11 public health units, though no cases have been identified in Toronto.

“The sharp increase in the number of outbreak cases and the geographic spread in recent weeks is due to continued exposures and transmission among individuals who have not been immunized,” Public Health Ontario said in its March 20 report.

New vaccine guidance

In Ontario, children typically receive two doses of measles vaccine – the first at one year of age and the second when they are four to six years old.

However, in his March 7 letter Moore recommended fast-tracking immunizations for individuals who live, work or otherwise spend time in the Grand Erie and Southwestern local public health units where he said that the risk of exposure is “higher.”

So far those two public health units have accounted for approximately 71 per cent of all measles cases in Ontario.

Moore is recommending that infants in those communities receive one dose of measles, mumps, rubella (MMR) vaccine between six months and 11 months, with two additional doses delivered after they turn one.

He says that children over the age of one should also receive their second dose of the vaccine “as soon as possible” rather than waiting until they are four to six years old.

As well, Moore is recommending that adults born before 1970 receive a second dose of vaccine. Ontario only began administering a second dose of the measles, mumps, rubella (MMR) vaccine in 1970.

“The provincial vaccine supply is being monitored and additional doses of vaccines are being ordered as needed,” Moore said in the letter. “Thank you for your continued efforts in ensuring Ontarians are protected from vaccine preventable diseases.”