The Centers of Disease Control and Prevention has issued new guidance regarding people who are infected with the coronavirus.
“People who have tested positive for COVID-19 do not need to quarantine or get tested again for up to three months as long as they do not develop symptoms again,” the CDC said in its updated guidance. “People who develop symptoms again within three months of their first bout of Covid-19 may need to be tested again if there is no other cause identified for their symptoms.”
The guidance, which pertains to quarantine, was updated last on August 3rd, but was first reported Friday by the New York Times. Throughout the pandemic, the CDC has not typically alerted the public when it updates one of its guidelines, even when the information is noteworthy.
The update was interpreted by the Times and several other media outlets to suggest that people who are infected with COVID-19 are conferred some, albeit perhaps not lasting immunity.
But late Friday, the CDC issued a statement saying, "Contrary to media reporting today, this science does not imply a person is immune to reinfection with SARS-CoV-2, the virus that causes COVID-19, in the 3 months following infection. The latest data simply suggests that retesting someone in the 3 months following initial infection is not necessary unless that person is exhibiting the symptoms of COVID-19 and the symptoms cannot be associated with another illness."
But some scientists have speculated that 3 months may be the duration of immunity for those who are infected. In June, a study published in Nature showed that a high proportion of patients began to show decreasing levels of immunity 2–3 months after infection. Moreover, especially in cases where individuals are asymptomatic or have less severe symptoms, the antibodies may not last very long.
The results threw into question the idea of governments issuing "immunity passports" that would enable infected individuals to travel and return to work.
Initially, experts believed that people diagnosed with covid would develop antibodies that result in immunity for at least a year. SARS and MERS, two other coronaviruses produce antibodies that are believed to last about that long.
But the scientific community, including the World Health Organization, has stopped short of saying that those who developed antibodies have immunity.
"There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection," the WHO said in April.
One concern has been the reliability of the antibody tests themselves.
Still, some have pointed to limitations of the June study. It had a small sample size, that of 74 people in China. Critics also argued that the researchers failed to take into account immune cells known as memory T and B cells that can also fight the virus and trigger new antibodies when another infection occurs.
"That antibodies decrease once an infection recedes isn’t a sign that they are failing: It’s a normal step in the usual course of an immune response," a pair of Howard Hughes Medical Institute professors wrote in a New York Times op-ed. "Nor does a waning antibody count mean waning immunity: The memory B cells that first produced those antibodies are still around, and standing ready to churn out new batches of antibodies on demand."
The authors also argued that the presence of declining antibodies does not mean that a vaccine will not offer lasting protection against the virus. Vaccines, they write, can produce a far better antibody response than natural infections.
While there have been anecdotes of people getting covid a second time, doctors said there was no evidence of a second infection.
The story has been revised to include a new statement from the CDC clarifying its guidance.
