Just how long is this COVID19 crisis going to last: the science suggest it will be many months - perhaps until the end of the year.

background 100By Staff

March 21st, 2020

BURLINGTON, ON

 

The following was first published by the Globe and Mail earlier today under the headline: Deciding when to end social distancing won’t be easy.

It looks like the effectiveness with which people distance themselves is going to have a huge impact,” said Caroline Colijn, a professor at SFU and Canada 150 Research Chair in mathematics for evolution, infection and public health.

To examine what that means for Canada, Dr. Colijn tested a range of possible futures. Each begins in mid-March with a tiny fraction of the population infected by the virus.

Importantly, the scenarios show the high level of uncertainty that is built into models of this kind.

Based on a slight difference in how easily the virus can be transmitted from one person to the next – a number that is not yet known to high precision – the fraction of the total population that is infected during the peak of infections can vary by as much as 15 per cent.

Another unknown is whether the virus will become less active during the summer months. This is what happens with seasonal flu, another respiratory virus, but the same effect can’t be assumed for a virus to which the human population has never been exposed. However, even if there is a seasonal effect, it would likely only serve to delay the trajectory of the outbreak rather than significantly change it.

Where the scenarios can provide some clarity is in the comparisons between different options for how much social distancing should be applied and for what length of time. Those comparisons are captured here.

Why distancing matters
The basic strategy is simple. If everyone in the population is isolated from everyone else, the virus has nowhere to go and infections die out over the course of the incubation period of 14 days. In practice it doesn’t work that way. Families will isolate together and it could take a number of weeks for a virus to move within a family group. And there is still a need for at least some people to be out and about performing essential services, including caring for the sick.

THE POWER OF ISOLATION

Distance G&G 1

Three scenarios show the impact of different levels of social distancing on a population that is susceptible to COVID-19. In the final case the wave of infections stretches out to nearly a year but peak infections and total number of cases are both significantly reduced.

These three scenarios compare the trajectory of the pandemic when no measures are taken with what happens under medium and strong levels of social distancing. The measures are interconnected in complex ways. For example, school closings and work-from-home recommendations greatly reduce the spread of the virus between students and co-workers, but increase the potential for household and local community contact as people spend more time in their own neighbourhoods. Shutdowns of social venues, including restaurants and cafés, can reduce contacts still further.

With no measures in place, infections rise quickly and reach their peak by about June. At that point, up to one quarter of the population could infected at the same time. In a large Canadian city, this would amount to hundreds of thousands of cases, many of them severe.

In the medium scenario, schools and some businesses remain open but social contact is reduced by up to 40 per cent. Here the peak is lowered somewhat and shifted by a month or so. The bigger difference comes if social-distancing measures are strong, with most places where people gathered closed for the duration of the pandemic. Then the height of the peak could be cut by more than one half and it doesn’t arrive until the early fall, by which time health facilities may be better able to meet the flood of new cases.

All three scenarios end with a significant fraction of the population having been infected one year from now. With no distancing, that amounts to more than 70 per cent of the population before the virus burns out. With strong distancing, it’s more likely to be less than half the population.

GOING THE DISTANCE

Distance G&M 2

Here, the scenarios show what happens when strong social distancing measures are lifted after one month, three months and six months. The first two cases only delay the pandemic, the third significantly lowers its impact.

These scenarios show what happens when the strong distancing measures are lifted after one month, three months and six months. Whether distancing ends abruptly or gradually, there appears to be little benefit to ending the measures before the peak of the pandemic is over.

For example, ending after one month merely displaces the steep infection curve that occurs with no distancing by roughly the same amount of time. Ending after three months – about July 1 – spreads the peak out a bit more, but it still reaches 20 per cent of the population infected by the end of the summer. Only the six-month interval, which means lifting measures around Oct. 1, significantly breaks the shape of the infection curve. Here the range of uncertainty is greatest, with a few per cent to 15 per cent of the population infected late in the year.

PLANKING THE CURVE

Distance G&M 3

If even stronger levels of social isolation are enforced, this scenario suggests that the number of infections within the community can be suppressed during the initial weeks and held to less than 50 cases per million people at any one time. However, the curve might still rise gradually, propelled by a few cases, and there would remain a constant risk of infection re-entering from other locations. When enforcement stopped, infection rates would be expected to rise quickly.

On Thursday, Canada’s Chief Public Health Officer Theresa Tam said the country must not only flatten the infection curve but attempt to “plank” it. That means pursuing every possible measure to its fullest, including social distancing and rapidly identifying new cases and isolating anyone who may have been exposed to the virus.

In that scenario, the pandemic does not take off. While the cumulative number of cases may run into the thousands, it only amounts to a tiny fraction of the population. In the model, this means reducing all contacts outside of the household by more than 90 per cent. If it works, community infections could be kept relatively low.

This option would require even harsher measures than Canadians are already practising. And since the vast majority of the population still has no immunity to the virus, there remains a strong likelihood that the infection rate will soar as soon as measures are lifted. And even if the virus is extinguished within the community, there remains the risk of it being reintroduced from elsewhere.

Return to the Front page
Print Friendly, PDF & Email

4 comments to How long is this COVID19 crisis going to last: the science suggest it will be many months – perhaps until the end of the year.

  • Reality time is that you can’t bend this curve significantly while you let people come in with fresh infections. We are still doing this, and until that gets stopped, you are just “delaying the curve,” not bending it. As of yesterday, 82% of infections are travel related. We are getting very concerned with corner cases – kids hypothetically spreading virus on a playground and theoretical “symptomless carriers.” Possible. However, we have an example from South Korea that had success without closing schools, for instance. But did focus on measuring everyone’s temperature. The bulk of highly contagious carriers had close contacts with those they infected and were actively sick. Thus where Tom is correct is that when infected are identified and placed under “self quarantine”, this needs to be monitored or enforced. This exactly what South Korea did – monitor – find – trace – isolate. They did not, however, randomly close things based on theoretical transmission and leave things like the subway open. Plus, we are getting lots of stores, “shrinking hours,” and closing extra days. This is simply jamming more people in the store at once – the opposite of what we want. Thus, I’d prefer to put a focus on isolating travellers, enforcing isolation, tracing contacts and spooling up health resources – this is the South Korea solution. Less focus on trying to close everything and freeze everyone in place a time-limited solution with people needing groceries, work etc … China reportedly did make that work in Wuhan, but as they release the lockdown they get fresh cases in and sort of spark up again. We go two glaring errors with letting new cases in, and if you are going to allow subway and GO Train – containment seems unlikely.

  • Joe Gaetan

    At the moment the Canadian case infection rate (date adjusted) is tracking closely to the experience in Italy. The question is, did we as a country act soon enough to “planck” the curve. Self isolation,hand washing, and social distancing are behaviours we need to take seriously, as short of a vaccine that’s all we as individuals can do.

  • Tom Muir

    Right off;

    – to plank we have to get testing, testing, testing, ramped up for everyone asap to the millions to identify the infected and get them isolated.

    We know how to do it so get it implemented assembly line style. This testing has been advised for months by WHO and many others.

    – Can someone in charge make the list of the strictest possible measures for the planking examples. Perhaps Dr. Tam can be contacted about this, although this is just an example of need for leadership in getting this together.

    – If people are still complacent order them in place.

    Stay Home. We can get fresh air and can get food in innovative and collaborative ways, but avoid all contact possible.

    Nobody ever said this was easy (except stupid T south of the border). It’s hard just to think about doing the things needed to suppress the infection rate immediately, as the planking figure shows.

    We have started this but now we need to bear down and push to get the infection numbers and the trend downward that we need and are capable of. No slacking

    It will be a very big and fatal mistake if we fail in this – Follow the Mayor.

    • Phillip Wooster

      Testing is absolutely critical–apparently Japan and Singapore, two countries which seem to have contained this virus fairly well, did the same thing–identified the infected and rigorously followed up on all contacts.

Leave a Reply