Blood tests can incorrectly detect coronavirus and may not be key to reopening nations yet, say experts
Even if some tests are more reliable, they cannot yet reveal whether someone is immune to the virus or not
Countries around the world are hailing blood tests as the key to freeing regions under lockdown. But can such tests — which detect the body's weapons called antibodies against the new coronavirus — tell whether people have fought off the virus and returned to normalcy?
At this stage, most experts believe antibody tests are imperfect. "We should keep in mind that there is a range of errors for these tests," Dr Tara C Smith, from Kent State University College of Public Health, told MEA WorldWide (MEAWW).
She added that these tests are capable of giving rise to two kinds of errors. It might incorrectly detect antibodies when people have none: false positives. Conversely, it might not detect antibodies even when the person does have them. The errors suggest these tests might not paint an accurate picture of COVID-19 prevalence in a community.
Even if some tests are more reliable, they cannot yet reveal whether someone is immune to the virus or not. According to the World Health Organization (WHO), these tests can show how widespread the infection is in a community. Data on immunity will take longer to come.
"There are a lot of countries that are suggesting using rapid diagnostic serological tests to be able to capture what they think will be a measure of immunity. Right now, we have no evidence that the use of a serological test can show that an individual has immunity or is protected from reinfection," WHO's technical lead on COVID-19, Dr Maria Van Kerkhove, said in a press briefing.
What are population-level antibody tests saying?
Experts are not writing off antibody tests yet. They are important. "If we find that a much larger percentage of the population has been infected than we currently assume, it may allow us to think about getting back to some semblance of 'normal' more quickly," Dr Smith said.
But early data indicates low levels of infection. The WHO estimates that only 2% or 3% of people appear to have antibodies to suggests an infection.
This estimate is lower than what experts had predicted. Dr Kerkhove said though the number of people infected would be higher, she stressed it was still too early to conclude. "Initially, we see a lower proportion of people with antibodies than we were expecting. A lower number of people are infected," she added.
Only 3% of the 7,000 people tested in the Netherlands developed antibodies against the disease. In a German town, the infection prevalence stood at 14%. But there are outliers. Studies carried out in two US counties — Santa Clara and LA county — suggest infection rates are much higher than official figures.
The Santa Clara study calculates that 2.5 – 4% between 48,000 and 81,000 of the population — in the county have had COVID19. The infection rate, according to the study, is 50-85 times higher than the official tally.
"Even though most experts agree that the real number of infected people is higher than the reported numbers, 50-85 fold higher than reported would be quite crazy. In research, we like to say that extraordinary claims require extraordinary evidence," Dr Pleuni Pennings from San Francisco State University, wrote in a blog post.
Earlier this week, another group of researchers released survey data on residents from Los Angeles County. According to them, antibody tests reveal that infection rates are 28 to 55 times more than the actual numbers.
What is more concerning is that both studies used an unvalidated antibody test. They used China's Hangzhou Biotest Biotech. The company, according to NBC, was recently banned from exporting COVID-19 tests by China because it had not been vetted for accuracy.
According to WIRED, the lead researcher of the LA county study acknowledged the test’s origins and added they were exported legally before the ban.
More inaccurate tests in the market
The US Food and Drug Administration (FDA) has approved only four antibody tests so far: Cellex, Ortho Clinical Diagnostics, Chembio Diagnostic Systems, and the Mount Sinai Laboratory.
But the agency has allowed more than 90 unapproved antibody tests to flood the market. The WHO has warned against the use of rapid antibody tests for diagnosis. Other countries have learned it the hard way. Britain purchased millions from China, only to realize they did not diagnose people with mild-to-moderate disease
"The problems mainly happen with rapid tests," Dr Giorgio Palù, an Italian microbiologist and former president of the European Society for Virology, told The New York Times. "They will never be able to tell the spread of the virus because they do not have the required sensitivity and specificity."
More large-scale testing in the pipeline
In a bid to speed up the reopening, New York governor Andrew Cuomo announced a plan to randomly select 3,000 people for antibodies. He said he would make his decision based on data and testing.
Other large-scale sample studies are currently underway. The National Institute of Health is looking for antibodies in six metropolitan regions in the US. Toward the end of the year, these tests will evolve into a nationwide survey with help from the Centers for Disease Control and Prevention (CDC).
In addition to helping scientists understand the extent of infections and immunity, it will also help develop vaccines.
In Europe, Germany has kickstarted a large-scale COVID-19 antibody testing to monitor infection levels in four hard-hit regions. According to the Robert Koch Institute, Germany's federal disease control and prevention agency, the tests will reveal how many people in the have gone through infection and are therefore immune.
Ulrike Leimer-Lipke, a doctor involved in the testing, told Euro News: "We know that, especially in Germany, a lot of people already had it. And it is also very important for them, especially if they have a grandmother, mother or father whom they look after, to know whether they are already immune."