In 2003 for example, prior to adoption of the current International Health Regulations, the WHO did advise travellers to avoid Toronto during the SARS outbreak. Then-mayor Mel Lastman may not have known about the WHO — "I don't know who this group is," he told CNN — but he wasn't wrong to criticize the UN health agency's travel advice at the time.
It did little to limit the impact of SARS globally, but it had a massive effect on the economy of Canada, and Toronto in particular, where the tourism industry alone lost an estimated $1.1 billion.