Just two months ago, the discovery that two people infected with the coronavirus had no symptoms was such big scientific news that it was published in the New England Journal of Medicine.
Now, it is becoming clear that much, if not most, of the spread of the virus is by infected people who don’t get sick. New evidence comes from a Boston homeless shelter, an Italian town, a California county, and a Navy aircraft carrier.
“With regard to COVID-19, we’re learning that stealth in the form of asymptomatic transmission is this adversary’s secret power,” Rear Adm. Bruce Gillingham, surgeon general of the Navy, said at a briefing earlier this month.
That secret power has huge implications for curbing the pandemic, and further dampens the prospects for safely reopening the United States before therapies or a vaccine are available.
Here is an overview.
Last month, German researchers shared a study of nine hospitalized patients. The patients released, or “shed,” coronavirus in their sputum and stool very early in their infections, and for up to a few weeks after symptoms ended. That suggested people might be infectious before and after they were sick, which would make stopping the spread even tougher.
Meanwhile, health officials were reassuring the public that asymptomatic transmission was unusual, and the virus mostly spread in droplets sneezed or coughed by a sick person.
More and more data contradict that reassurance.
The Navy tested the entire 4,800-member crew of the coronavirus-stricken aircraft carrier Theodore Roosevelt. Over 600 sailors tested positive, yet 60% of them had no symptoms such as fever, fatigue, or cough, Reuters reported.
At a Boston homeless shelter, an outbreak prompted testing of 397 people. Of the 146 people who tested positive, none was considered symptomatic, CNN reported.
In Santa Clara, Calif., Stanford University researchers early this month used Facebook to recruit a representative sample of 3,330 residents. Using blood tests that look for disease-fighting antibodies to coronavirus — a sign of previous infection — the researchers estimated that between 2.5% and 4% of the population had contracted the virus. That suggested the actual number of infections was 50 to 85 times more than the number of confirmed cases.
In Vo, Italy — where that country’s first coronavirus death occurred — the whole town was locked down in early March and all 3,000 inhabitants were tested. Not only did this enable containment of the virus, but it provided epidemiological clues.
“At the time the first symptomatic case was diagnosed,” a University of Padua researcher wrote in the Guardian, “a significant proportion of the population, about 3%, had already been infected — yet most of them were completely asymptomatic.”
In the U.S., diagnostic testing for COVID-19 has gone from practically nonexistent to severely rationed. Big companies are now marketing the complex molecular tests, but the number of tests per day has plateaued at about 145,000, according to the COVID Tracking Project. Testing continues to be plagued by backlogs and shortages of needed chemicals, swabs, and face masks.
The bottom line: If you are infected but don’t have symptoms — as lots of people apparently are — you can’t get a diagnostic test.
Michael Mina, an epidemiologist and infectious disease specialist at Harvard University’s Chan School of Public Health, said testing has been so inadequate that estimates of rates of transmission, death, and immunity are shots in the dark.
“How off we’ve been is hard to say,” he said during a teleconference last week.
A simpler type of test that measures blood antibodies — like the test used in Santa Clara — is just beginning to be marketed. In theory, a person who has recovered from COVID-19 will have antibodies that confer protective immunity — at least for a year or two.
Antibody tests have been touted by health and government officials as a way to identify workers, particularly those in essential jobs, who can safely lead the return to normal life.
But just like coronavirus diagnostic tests, antibody tests have been plagued by problems. The logistics of antibody surveillance, called “seroprevalence” testing, are unclear, so researchers and health departments (including Chester County’s) have randomly jumped in to start doing it.
The accuracy of antibody tests is also unclear, partly because they are basically unregulated. The U.S. Food and Drug Administration said companies could market such tests without regulatory review — and then warned companies to stop falsely claiming their tests were FDA approved or authorized.
“The FDA has really swung the pendulum, in my opinion too much,” Mina at Harvard said. “Things are getting [to market] that probably shouldn’t be.”
On Saturday, FDA Commissioner Stephen Hahn issued a statement saying its approach to COVID-19 testing “has been a careful balancing of risks and benefits to meet urgent public health needs,” and the agency “still expects tests to be validated.”