OTTAWA -- Answering criticism that the federal "COVID Alert" app only works on newer smartphones, Dr. Theresa Tam says it's one of many tools in fighting the novel coronavirus.

The app released last week is meant to tell users if their phones have recently been close to a phone registered to someone who volunteers that they've tested positive for COVID-19. But it works only on phones released in the last five years or so because it needs a relatively recent operating system.

Critics say that will leave out poorer and older Canadians, who are more likely to use older devices and suffer worse effects from the virus.

Tam said she's heard that criticism and understands it, but the app isn't supposed to be a comprehensive solution to the pandemic.

"It may not be the broadest coverage that you need," Tam said in an Ottawa news conference Tuesday, "but what if, for example, before you walked into a pub, before you walked into a nightclub or places where there may be a bunch of people you may not know, who are not in your specific social circle, where notification is particularly important?"

Younger people with newer phones are an "extremely relevant" target for the app, she said, as are people working in offices who might have more current employer-issued devices.

"Despite these gaps, we need to have a go at using it," Tam said.

A spokesman for the Treasury Board said Tuesday that as of Monday evening, the app had been downloaded 1.3 million times.

He said it's not possible to track how many exposure alerts had been sent out.

Tam said we need to use every tool we have to fight the pandemic, even if they aren't perfect.

"For the hard-to-reach populations, public health will still be doing, as rapid as possible, the contact tracing ... that's required," Tam said.

This report by The Canadian Press was first published Aug. 4, 2020.