Blood tests will tell us when normal life returns
Serological tests will provide better picture of how COVID-19 has spread through the community
There’s been a lot of discussion about testing as the coronavirus outbreak has unfolded, but the really important COVID-19 test isn’t even in use yet.
And that’s the one that could well determine when it’s safe for life to head back toward normal.
Canada and the rest of the world are waiting for an accurate, reliable serological — or blood-based — test to be developed and approved for use.
Serological tests, Health Canada states, will play an important role “in assessing the true extent of COVID-19 in the general population.”
“But these are not simple things to develop and validate,” said Dr. Doug Sider, an epidemiologist and physician with Hamilton’s public health department. “This is a new organism.”
The current swab tests only look at the present by showing who is or isn’t infected.
It’s simply a yes or no result taken
at that point in time and the results can only give a vague outline of how COVID-19 has spread through the community . The swab tests also give no indication of the severity of the disease.
Many of the swab tests given so far haven’t been random. They’ve been targeted at people with obvious symptoms, health-care workers, and longterm care and retirement home residents.
It’s likely that current testing is ignoring a significant number of people who have been infected but developed no symptoms or only mild symptoms.
A serological test, ironically, looks at the past to predict the future.
The test, when eventually developed, will show whether or not antibodies — evidence the body has produced an immune response to infection — are present in blood.
When blood tests are rolled out, they can help show the numbers of people who have been infected, especially those who may not even know it, and what level of immunity might exist in the community.
A serological test is similar to election polling, where a sample of results, selected wisely, can give you a good picture of how the population as a whole is behaving.
It’s important for public health officials to know what proportion of people have immune protection to the novel coronavirus. Experts suggest that so-called “herd immunity” will require 60 to 70 per cent of the population to have protection, either from a previous infection or a vaccine, which is even farther down the road than a blood test.
Swab tests are only showing the tip of the iceberg, stated Dr. Timothy Evans, an expert at McGill University.
“What we can’t see, below the surface, are the people who’ve been infected but whose symptoms have been mild or nonexistent, as they were not tested,” Evans stated recently. “Serological testing will give us a sense of just how many people
make up the base of the iceberg.”
But serological testing isn’t going to answer all of the questions about when it will be safe to resume everyday life.
“The question is what does it mean if you have those antibodies?” said Dr. Mark Loeb, a McMaster University infectious diseases specialist.
“Does that protect you and if it does, how long does it protect you for? And that’s unknown.”
On April 24, the World Health Organization published a COVID-19 update with a worrisome warning on that topic. The WHO shot down the idea that previously infected people could be provided with an “immunity passport” that could allow them to return to work or travel.
“There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” the WHO stated.
There will also be the question of whether or not the province and public health departments will have the resources to ramp up blood sampling once a test is approved.
“Will we have the lab capacity?” asked Sider.
Sider said the city’s public health department would want to test hundreds of people to get an accurate picture of Hamilton’s infection rate.
“I’m not interested in a thousand people tested at the level of Ontario,” said Sider.
“But you’re talking about thousands if not tens of thousands of people who would need to be tested across the province to allow us to get an accurate picture in Hamilton, in Kingston, in Toronto, in Barrie and so on.”
The other challenge to developing a serological test is to ensure it doesn’t record a high rate of false positive results.
“We will learn a great deal from serological testing,” said Sider, “but we’ll also have to be extremely mindful about some of the potential limitations and how it helps us to understand, predict and prepare for the next possible waves of pandemic.”