In late February, the government of Osaka, Japan, announced that a female tour bus guide in her 40s may have caught COVID-19 for a second time. Around the same period, reports from China indicated that some patients were being readmitted to hospitals days or weeks after getting discharged with negative tests.
Stories about coronavirus patients testing positive for the illness after they thought they had recovered have cropped up around the world ― including in the U.S., where a WNBA player in Arizona said she believed she was on her second infection.
“It’s just so unknown; we have to be extra careful,” Phoenix Mercury guard Sophie Cunningham told reporters earlier this month.
Cunningham is correct that there is still much we don’t know about how the virus functions and that we should, therefore, take care to follow safety protocols. But scientists would like you to take reinfection stories with a healthy dose of skepticism.
Is it technically possible to get COVID-19 two separate times? Yes, Buffalo University infectious disease professor Thomas Russo told HuffPost this week. But how likely that is ― and how exactly it happens ― is “really something we don’t know yet,” Russo said.
One huge factor is the accuracy of coronavirus testing.
No COVID-19 test is absolutely perfect, and differences in their designs and materials can mean that some are more or less accurate than others. For example, the Food and Drug Administration issued a warning to labs earlier this month about a test called BD Max, alerting them that one study found an increased risk of error: 3% of results using that test were false positives. The type of test a patient receives is generally up to her health care provider.
Because the diagnostic tests are designed to look for parts of the virus’s RNA, false positives can also arise when a dead fragment of the virus is detected in a patient ― meaning that the patient made a recovery but still has bits of the virus’s genetic material in his system that are not infectious.
Variables in testing mean that a number of possible scenarios could play out. It’s complicated, too, because we know that symptoms of COVID-19 can vary widely. Some people do not experience any at all while others present them for weeks, even if they don’t have a severe case. Scientists are still learning why.
Given all of that, a patient could falsely test positive then accurately test negative before she actually picks up the virus and falls ill, leading her to suspect she might have had it twice.
In another case, a false negative test could lead a patient to believe he’d recovered when he was actually still battling the virus.
Others might accurately test positive, appear to get better over several weeks, then test positive again ― but the test merely picked up dead fragments. That appeared to be the case for a health care worker in Hawaii, who tested positive three weeks after recovering from symptoms.
In Osaka, it remains unclear what precisely happened with the tour bus guide. She tested positive in late January and tested negative several days afterward before returning three weeks later to a health care center with a sore throat and again tested positive for COVID-19.
We don’t know exactly how antibodies protect us from this virus.
When a person is infected with a virus, she often begins producing antibodies as a defense mechanism that helps prevent reinfection. Unfortunately, we don’t know a lot about how COVID-19 antibodies work and how much protection they may give us.
A recent study from King’s College London ― the largest of its kind so far ― suggested that the antibodies might not be as effective as hoped. When scientists looked at the immune responses of more than 90 COVID-19 patients, they found a steep drop in antibodies three months after infection. (The study has not yet been peer-reviewed.)
“People are producing a reasonable antibody response to the virus, but it’s waning over a short period of time, and, depending on how high your peak is, that determines how long the antibodies are staying around,” the study’s lead author, Dr. Katie Doores, told The Guardian.
Doores’ research helps support the idea that the new coronavirus may be able to reinfect people year after year, like the flu ― which could mean that any vaccines approved to fight the virus’s spread may have limited effectiveness.
Antibodies aren’t the body’s only defense mechanism, though.
“Decreasing antibodies doesn’t necessarily mean that you’re going to be susceptible for reinfection. There’s a very important part of our defenses called cellular immunity, and some of these cells are memory cells for producing antibodies,” Russo said. “There’s also other types of cells that could directly kill the virus,” he said, such as T cells that eliminate infected cells.
“It’s something that people are keeping an eye on very carefully,” Russo said.
He continued: “I think that it’s somewhat encouraging that we’ve had millions of cases around the globe, and the fact that we haven’t had any clear-cut reinfections certainly suggests that the host response to natural infection must be protection at least for a few months.”