Canada faces the alarming possibility of losing its measles “elimination” status as an outbreak of the disease is spreading across the country. 

The designation, set by the World Health Organization, is in jeopardy if sustained transmission is not stopped by October, a year after the outbreak first began in Canada.

By May 10 of this year, there had already been 2,161 measles cases — 1,888 confirmed, 273 probable — according to the Canadian government’s health website. In all of 2024, Canada recorded a total of 146 cases.

The outbreak in Canada dwarfs the number of cases in America, which has a population eight times that of Canada. So far this year there have been 1,046 confirmed measles cases reported from 31 jurisdictions in the United States, according to the Centers for Disease Control and Prevention. Measles was officially eliminated from the United States in 2000.

Elimination status is defined as the absence of regular, endemic transmission of the virus within a country or specific region. Unlike eradication, which is the global cessation of person-to-person transmission, elimination only pertains to a specific geography. A country risks losing this status if the virus continues to spread for more than a year.

“The risk is substantial,” a public health physician with Public Health Ontario, Sarah Wilson, who has been closely monitoring the outbreak, told the Canadian Broadcasting Corp. “It is a very different situation than what we experienced in the last decade since measles elimination was achieved.”

Canada currently has the highest number of measles cases in the Americas, according to the Pan American Health Organization. Canada’s vaccination rate declined between 2019 and 2023, to 83 percent from 90 percent, according to the PAHO, leading to speculation that that could be a cause.

Measles is one of the most contagious infectious diseases in the world, more so even than influenza, chickenpox and Covid-19. The high level of transmissibility is the main reason measles outbreaks spread rapidly, particularly in areas with low vaccination rates.

Ontario has reported a surge in measles cases, with the province now seeing more weekly cases than it did in an entire decade after achieving measles elimination. Last week, there were 194 new cases for a total so far this year of 1,654.

The Americas achieved a historic milestone in 2016, becoming the first region to eliminate measles entirely. However, after outbreaks in Venezuela and Brazil, the region lost this status three years later, only to regain it in 2024. Now, with Canada’s outbreak, the region’s status is once again at risk.

Brazil’s efforts to address its outbreak could provide a potential roadmap for Canada. Targeted vaccine campaigns, expanded molecular testing to track the virus, and training rapid response teams were key strategies in ending its outbreak, according to PAHO.