The R number, or reproduction number, of the novel coronavirus in Alberta has been trending down the last couple months, according to numbers provided by Alberta Health on Thursday.
The R number provides insight into how the virus is spreading and is determined by how many new cases a single case generates.
For example, a R number of one means one person infects one other person, while a R number of two means one person infects two others.
An R of two could create a situation where the virus gets out of control: one person infects two, who infect four, who infect eight, who infect 16, who infect 32 and so forth. Each doubling would happen roughly every five days, and in theory, the process only stops when the virus has infected the whole population, which in Canada’s case, would happen at about the four-month point.
In Alberta, the R number was 1.7 on April 8, 1.4 on April 28 and 1.2 on May 1.
“ still slightly more cases generated from each new case than we would like to see,” said Dr. Deena Hinshaw, Alberta’s chief medical officer of health, about the most recent R number of the virus.
“We would like to see that at one or lower. We’ll have to be watching very closely to see how that trends over time as we move into relaunch.”
University of Toronto epidemiologist Ashleigh Tuite said it is a good thing when the R number falls below one.
“That basically means that each case is, on average, making less than one new case, we’ve exited the exponential growth phase of the epidemic and we expect to be able to control the outbreak and, eventually, we hope that it would die out.”
Most of the province moved into Phase 1 of relaunch on Thursday, meaning some retail stores, restaurants and museums and galleries can now welcome patrons.
There is a slower phase-in of Phase 1 in Calgary and Brooks due to the fact that the two municipalities together make up three-quarters of the confirmed cases in the province.
The province may now be beginning to reopen its economy, but Dr. Hinshaw said it is important to keep up with public health measures like staying physically distant, washing hands frequently and staying home when sick.
Those measures can help bring the R number down.
“That could be that you’ve reduced the number of contacts that you have because of physical distancing, it could be that you’re really good at identifying people who are infected and isolating them, so that they’re not able to transmit to other people… that would be another reason how you would reduce that reproductive number and keep it below one,” Tuite said.
–with files from Patrick Cain
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