Months into the pandemic, the scientific community’s understanding of Covid-19, the illness caused by the new coronavirus, is rapidly evolving. New reports of patients testing positive, or appearing to suffer symptoms months after initial diagnosis, continues to generate concern that people who have had Covid-19 are getting infected anew.
Here is the latest on what we know, and don’t know, about the possibility of becoming sick with the virus more than once.
I recently recovered from Covid-19. Does that mean I can’t get it again?
Most scientists say that people who have had Covid-19 gain some immunity to the virus that causes it. What they don’t know is whether that protection lasts a few months, a few years or a lifetime.
What factors affect immunity?
The immune system wards off infections by producing antibodies that fight invaders. A range of hereditary and environmental factors, including diet and sleep patterns, typically affect the strength and longevity of those defenses.
Immunity also depends on the pathogen. For example, infection by the virus that causes measles confers lifelong immunity. Others, like the influenza virus, can mutate so rapidly that protective antibodies might not recognize them during a reinfection.
The novel coronavirus mutates more slowly than the influenza virus. That gives researchers hope that any natural immunity, or vaccine, would offer more lasting protection. Even if someone gets sick again, researchers believe a second infection might be milder than the first.
How soon would my body produce antibodies to fight the novel coronavirus after an initial infection?
The U.S. Centers for Disease Control and Prevention says antibodies develop within one to three weeks after infection.
A study involving 34 hospitalized cases in China found that two patients, both in their 80s, produced antibodies within three days of symptom onset. The rest produced them two weeks after symptoms first surfaced. The findings were vetted by other experts and published in an academic journal in March.
Is there any good news?
A group of Chinese researchers reported this month that they had infected six rhesus macaques, allowed them to recover and then reinfected four of them 28 days after the first infection. None became sick again, showing their immune system shielded them from a second infection.
The research, published in Science, says, however, that more studies are needed to understand whether the immune system can shield individuals from reinfection over longer periods of time.
Then why are some people testing positive again?
Roughly 450 South Koreans tested positive for the virus again after meeting the criteria for recovery and being discharged from isolation. The Korea Centers for Disease Control and Prevention re-tested more than half of those people and found no evidence of the live virus circulating.
Peer-reviewed research studies have shown that viral fragments can circulate even after an individual is symptom-free. That doesn’t mean that people are still sick or infectious.
How do I know I’ve fully recovered?
Clinicians have mixed views on what constitutes recovery because long-term data aren’t yet available. Guidelines vary across the globe.
For example, the CDC says that infected individuals are considered recovered if they test negative for the novel coronavirus twice, with tests approved by the U.S. Food and Drug Administration taken at least 24 hours apart.
Or, individuals must be fever-free for three consecutive days and show an improvement in their other symptoms, including reduced coughing and shortness of breath. At least 10 days should have passed since their symptoms first surfaced.
Some survivors testing negative for the virus say that certain symptoms, such as a loss of taste and smell, can linger for months after other symptoms are gone. Agencies