Toronto Mpox Clade Ib: New Cases & Updates

Toronto public health officials have confirmed the first cases of the mpox clade Ib variant in the city and province of Ontario, signaling a potential shift in the circulating strains of the virus. While mpox hasn’t disappeared – 155 cases were confirmed in Toronto in 2024 alone – this marks a change from the dominant IIb strain seen since the 2022 outbreak. This isn’t simply a case of a new variant appearing; it highlights the ongoing global circulation of mpox and the increasing likelihood of diverse strains entering Canada through international travel.

Since the initial global outbreak in 2022, mpox (formerly known as monkeypox) has largely been associated with the IIb clade, particularly within networks experiencing close, intimate contact. Clade Ib, however, is more commonly found in parts of Central and Eastern Africa. Its appearance in travelers to Europe and now Toronto suggests increased international spread, potentially linked to relaxed travel restrictions and evolving transmission dynamics. The fact that prevention and treatment protocols remain the same for both clades is reassuring, but it doesn’t diminish the need for vigilance.

The concentration of cases in Toronto’s downtown core in 2024 suggests specific community-level transmission patterns that public health officials will likely continue to monitor closely. This localized clustering emphasizes the importance of targeted outreach and vaccination efforts within high-risk populations.

The Forward Look

The identification of clade Ib in Toronto is a critical early warning. We can anticipate several key developments in the coming months. First, increased genomic surveillance will be essential to track the prevalence of both Ib and IIb strains and identify any further emerging variants. Second, public health messaging will likely be updated to emphasize the ongoing risk of mpox, even for those previously vaccinated against the IIb strain. While prior smallpox vaccination offers some protection, a targeted mpox vaccine is still recommended.

More broadly, this situation underscores the need for sustained investment in global health security. The rapid spread of mpox, and now the emergence of different clades in new regions, demonstrates how quickly infectious diseases can cross borders. Expect to see renewed calls for international collaboration on vaccine development, distribution, and surveillance – not just for mpox, but for other potential pandemic threats. The focus will shift from reactive outbreak control to proactive, preventative measures, including bolstering global capacity for early detection and rapid response.