Hundreds of people might have been exposed to measles at Montreal NATO summit: public health

This undated image made available by the Centers for Disease Control and Prevention on Feb. 4, 2015 shows an electron microscope image of a measles virus particle, center. (Cynthia Goldsmith/Centers for Disease Control and Prevention via AP)

Public health officials said Friday that hundreds of people may have been exposed to an unvaccinated person with a confirmed case of measles during the NATO parliamentary assembly in Montreal last month.

This marks the city's first known contagious measles case since July.

People may have been exposed between Nov. 23 and 26, though "the risk of infection is considered very low for individuals who have been adequately vaccinated," said Geneviève Paradis, a spokesperson for Montreal public health, in an email to CTV News.

An alert was issued to health-care professionals in Montreal Friday, noting the locations of potential exposure:

• The 70th Annual Session of the NATO Parliamentary Assembly at the Palais des congrès de Montréal on Nov. 23, 24 and 25.
• The Montreal airport on Nov. 26 before 5:09 p.m.
• Air Canada Flight AC417 leaving Montreal-Trudeau airport from Gate A49 on Nov. 26 at 3:09 p.m. en route to Toronto-Pearson airport at Gate D31, landing at 4:38 p.m.
• The Toronto-Pearson airport on Nov. 26 between 4:38 p.m. and 9:18 p.m.
• Air Canada Flight AC890 leaving Toronto-Pearson airport at Gate E71 at 7:18 p.m. on Nov. 26 en route to Italy's Rome-Fiumicino airport in Terminal 3, landing on Nov. 27 at 9:40 a.m.

The alert said the person with measles also attended other events related to the NATO summit, including:

• A private event at the Montreal Science Centre (La Passerelle and La Perspective rooms) on Nov. 23 from 7 p.m. to 9:30 p.m.
• A private event at the restaurant Pangea (104, rue Saint-Paul Est) on Nov. 23 from 7 p.m. to 11p.m.
• A private event at Cirque Éloize (417, rue Berri) on Nov. 24 from 7 p.m. to 11:30 p.m.
• The Westin Montréal (70, rue Saint-Antoine Ouest) between Nov. 23 and 26;
• The DoubleTree by Hilton Montréal (1255, rue Jeanne-Mance) between Nov. 23 and 26
• The Humaniti Montréal (340 De la Gauchetière West) between Nov. 23 and 26.

A measles outbreak in Quebec that emerged in early 2024 ended in June, with 51 confirmed cases, though a few additional cases have been reported since then, according to Quebec public health. Officials conduct an investigation whenever a measles case is confirmed to determine the source of the infection and find out who may have been exposed.

Measles is a highly contagious disease and people who are more at risk of complications include babies under one year old, people with a weakened immune system, and pregnant people who are not adequately vaccinated against measles.

More information on the disease and how to get vaccinated is available on the Government of Quebec website.