By last week, more people in B.C. had recovered from COVID-19 than had tested positive for it.
As of April 8, 1,336 British Columbians had tested positive for the virus. But 830 of them are now deemed to have recovered, and should therefore now have immunity.
In other words, it should be safe for them to resume normal activities, like going to work, since they are no longer infectious and should now have some immunity to the virus.
But the number of British Columbians who are immune could be a lot higher than 830, since many people exposed to the virus never get sick, or have only mild symptoms, and therefore never get tested.
In a paper published in medRxiv, a group of Oxford University scientists say that in the weeks between an outbreak and first recorded deaths, “the accumulation of significant levels of herd immunity” should have already occurred in a given population.
The problem is that there may be no way of knowing just how many people already have immunity in a given population without widespread and reliable seroprevalence testing.
Serology-based tests don’t test for the virus itself – they test for the antibodies that result after someone has been infected.
Serological tests could be a valuable tool, both for epidemic modelling, and for the economy, since it would tell public health officials who might be able to go back to work without the risk of infecting anyone or getting infected themselves.
Stephen Cann, clinical professor with the University of British Columbia’s (UBC) school of population and public health, said seroprevalence testing could be helpful, in terms of getting a better understanding of the disease’s prevalence, but said testing for the active virus is still more important.
“It could be useful,” he said. “You can’t test the whole population, but trying to get a rough estimate by random sampling could give you an estimate of how widespread the disease is.
“I think overall the COVID testing is more important. That’s something that could be added on, but it would be of secondary importance.”
He agrees that serological tests could be valuable in economic terms, since it could verify people to go back to work.
“As each week passes, the economic burden increases quite bit, so if you are using it to certify people to go back to work, it might be useful from that perspective – just in terms of the economy.
“The data we have so far seems to suggest if you had the infection then you’re not going to get it again, probably, this season. It may mutate over time. It may change next season.
In the absence of serological tests, public health officials are left with some very blunt tools – shutting down significant parts of society and the economy – which may be effective in delaying viral spreading, but is devastating for the economy.
Serological testing might allow for a much more targeted approach. Germany is said to be flirting with the idea of using blood tests to issue “immunity certificates,” for example, that would allow those people to resume normal routines.
One new serological test, developed by Cellex, has been approved by the Food and Drug Administration in the U.S., but Health Canada is in no rush to approve it here.
“These tests are also being accepted for review; however, the World Health Organization does not currently recommend serological tests for clinical diagnosis and Health Canada is following this advice,” Health Canada said in an email to Business in Vancouver.
“Research into serological testing is ongoing within Canada and worldwide. The department is working with the National Microbiology Laboratory to validate testing and research, along with expert advice, so that we can have confidence in the test results.”
In the absence of either seroprevalence testing, or more widespread testing for the virus, a group of UBC engineers and data scientists suggests that the best yardstick might be intensive care numbers.
Daily confirmed case numbers, based on testing, don’t provide an accurate picture of how widespread the virus may be within a population, because they are only snapshots.
“In an ideal world, yes, we would test everybody,” said Guy Dumont, a UBC professor of electrical and computer engineering, who specializes in adaptive and predictive control. “Unfortunately we’re not there, and we’re still quite some time away from having simple, cheap and rapid tests.”
Dumont and two of his UBC colleagues recently proposed an “on-off” intervention approach, based not on total COVID-19 cases but on intensive care numbers.
At some point, as the number confirmed cases begins to fall, the restrictions now in place will be lifted. But there could be a second and even a third wave, requiring those blanket restrictions to be put back into place.
“One suggested public policy to relax social distancing measures is an on-off approach, where some restrictions are lifted when the number of new ICU cases is below a threshold, and are put back into place when it exceeds a certain number,” they write.
Using ICU numbers as well as demographics – age and region, for example – restrictions could be imposed or relaxed in a more targeted way, as opposed to on-again off-again blanket shutdowns.
“Relaxing all restrictions when the number of infections has come down will only lead to a second surge in infections that will overwhelm our hospitals and lead to a higher mortality rate,” Dumont and his colleagues write.
In the “feedback modulation” approach that they propose, restrictions would be put into place, and relaxed, based on ICU numbers, not total confirmed cases, and would be more discriminating.
“We could have restrictions that are age-based,” Dumont said. “We could have restrictions based on the health status of people. We know that people with chronic conditions…are more susceptible. And we could also have restrictions based on geography.
“To be clear, we don’t want to speak in place of the public health experts,” Dumont said. “The only thing we’re saying is we think we have an additional tool here that they should find useful.”
Jason Goto, CEO of AnalysisWorks, which analyzes health data, has been studying how Canada stacks up against other countries when it comes to managing the pandemic.
He said the feedback modulation approach that Dumont and his colleagues are proposing seems reasonable, though he thinks it’s a bit premature.
“At some point we need to figure out our ‘release valve’ on getting back to normal, and critical care capacity is the best way to do it for sure,” he said.
But he added: “First things first. We here in B.C., in Canada and across the world need to consistently reduce our daily new numbers before we introduce the idea of getting back to normal.”
Goto said there simply isn’t enough testing being done, so the daily case numbers published each day in B.C. may not be giving the full picture of just how prevalent the virus is in B.C.
“Unless we test everybody, or start doing randomized testing on the general population, we are never going to know the ‘real numbers,” Goto said. “Given the scarcity of tests currently available, our only option is really randomized testing.”
On April 13, B.C. public health officer Bonnie Henry said she has gotten word that a serology-based test will be available in Canada soon.
“I’m very excited to know that that’s going to be coming online in the next week, 10 days,” she said. “We’ll talk more about this later this week about how we can use serology to better understand the pandemic so far and how we can use it to support our measures going forward.”
