Are we starting to flatten the curve?

The Citizen has asked a group of medical and research experts to answer reader questions about COVID-19. Here’s today’s query, on whether we’re seeing an impact from our actions (we’ll try to answer other questions as we receive them).

Public health experts have noted that the COVID-19 curve may be flattening in British Columbia. At the same time, we are being told that, despite this good news, we should continue to keep a physical distance and perhaps even more intensely. Why?

(Courtesy of Earl G. Brown, emeritus professor of virology, University of Ottawa)

To effectively slow an epidemic, the number of new infections must be reduced and the number of sick who recover must increase. If physical mitigation approaches are abandoned too early, effectiveness is reduced and a rapid resumption of epidemic growth will ensue. The initial response in British Columbia is encouraging but is not yet fully effective; therefore, as a population we must be guided by epidemiological principles and modelling to slow the pandemic so we can effectively deal with everyone who needs care.

A bit more detail:

The virus causing COVID-19 (SARS-CoV-2) must infect new people to continue to exist in the human population. If we isolated every patient until they no longer shed virus, we could end the pandemic now. However, this is no longer a practical solution.

We have passed from the first phase of pandemic response — which is containment of all infections (identifying all the sick with isolation and those they are in contact with) — to the mitigation phase to lessen the disease’s impact. The R0 (rate of spread of infection) for the COVID-19 virus is around 2.2, which means that one infected person will infect more than two others, such that each cycle of infection and spread takes around two weeks to produce repeated doublings (this is termed exponential growth). That’s one week for the initial patient to become ill enough to spread infection and another one week for the newly infected to become sick. Thus, two weeks is the bare minimum length of isolation to interrupt one iteration of this cycle of infection, especially as patients can transmit virus for longer than that.

The objective of physical distancing is to lessen the severity of the pandemic in the population by slowing and blocking its spread.

This, in turn, will lessen the demand for life-saving medical treatment and, hopefully, delay the pandemic to the end of a respiratory virus season that already puts a large demand on intensive care. If our hospitals are overrun with severe patients, the mortality rates will go up because patients that could live with life support will die due to a shortage of it. In Canada, 2.5 per cent of diagnosed cases need intensive care (half of what is seen in China).

In addition to slowing the progression of infections, we will gradually increase the resistance of the whole population by “herd immunity” through the increase in the number of recovered patients who hopefully will be protected from reinfection. This will decrease the R0 to less than one, which assures virus extinction at that point.