SARS was eradicated. MERS was eradicated.
Every other coronavirus we've discovered, though, remains in circulation.
That raises an obvious question: Which way will SARS-CoV-2 go?
Have we missed our window to rid ourselves of it? Now that it's mutating into more infectious forms, is it destined to remain with us for the rest of our lives?
Or is there still a chance that we can take it out for good, that effective vaccinations will eliminate its ability to survive by spreading from person to person?
The World Health Organization (WHO) thinks it's too late for that kind of optimism. Its leaders were openly discussing COVID-19's future as endemic -- that is, permanently circulating -- as early as last May, arguing that even at that time there had been too much transmission of the novel coronavirus for it to ever be fully eliminated.
Back then, the comparison point for WHO emergencies chief Dr. Michael Ryan was HIV. While HIV remains an active virus, it is closely monitored and there are effective treatments. Ryan suggested the virus that causes COVID-19 could end up in the same position.
That's one possibility. Another is that the virus starts attacking its hosts differently or targeting different hosts, becoming even more dangerous.
Ryan referenced this scenario much more recently. Asked Jan. 25 about the possibility of SARS-CoV-2 becoming endemic, he noted the long history of diseases that are now thought of as "diseases of childhood," but started out by attacking all age groups.
"Very often the disease – and this is a sad fact – in historical terms, very often killed many, many people and then as the disease moved into younger people, as older people became immune, the only new susceptibles were in younger kids as they were born," he said.
Another possibility, in-between those two extremes, is that the emergence of COVID-19 variants is hinting at the path forward.
The B.1.1.7 variant was first identified in the United Kingdom, and has been detected in nearly 400 COVID-19 patients in Canada, according to CTV News data. One of its hallmarks is that it appears to be more infectious, spreading more easily from person to person.
That's normal behaviour for a virus, according to Dr. Sumon Chakrabarti, an infectious diseases specialist at Trillium Health Partners in Mississauga, Ont. He told CTVNews.ca that just as humans try to keep viruses at bay, viruses adapt to better evade our defences and to stop themselves from killing too many of us.
"Naturally, with pandemics, you'll see that viruses may start to become more transmissible – but then they become less severe," he said Feb. 3 via telephone.
"They don't want to kill the host. That's not advantageous to it from an evolutionary standpoint."
-- with files from CTV --