Months after a pandemic that has caused more than 500,000 deaths worldwide, scientists are still trying to answer crucial questions about the coronavirus.
The main one of them: all about asymptomatic patients.
People who contracted COVID-19 but did not get sick and had no symptoms have been one of the most confusing factors in the ongoing public health emergency. Currently, the United States has more than 2.5 million confirmed cases of coronavirus, but many asymptomatic individuals are likely to have been forgotten by official accounts.
Now, scientists say that without a better understanding of how many people have been infected asymptomatically, it is difficult to know precisely how these people contribute to the spread of the virus and whether asymptomatic patients have developed antibodies or other protections that would confer some form of immunity. . against reinfection
Dr. Jorge Mercado, a pulmonologist and critical care physician at New York University’s Langone Hospital Brooklyn, said most of these questions stem from the fact that scientists are still not sure why some people who have When exposed to the virus, they become seriously ill, while others do not develop symptoms.
“We really don’t know much about this disease,” he said. “We know a little more than three months ago, but there are still many things for which we have no answers.”
Public health officials are still struggling to control the true number of people who have been infected. The Centers for Disease Control and Prevention said Thursday that the number of cases of COVID-19 in the US, including those that are asymptomatic, may be 10 times higher than what has been reported, which means that the true case count could be closer to 23 million.
“Our best estimate right now is that for every reported case, there are actually 10 other infections,” Dr. Robert Redfield, CDC director, said Thursday.
At first, many asymptomatic cases went unnoticed because states were dealing with a severe shortage of test kits and supplies that limited testing capacity to only the sickest of patients. As such, many asymptomatic people probably had no idea they were ever positive, said Dr. Marybeth Sexton, an assistant professor of medicine at Emory University in Atlanta.
“We tend to spot asymptomatic or mildly symptomatic people when we follow up on contacts, so when we find someone who is positive and start evaluating people they’ve been in contact with,” he said. “I think it will be a long time before we know for sure what the actual percentage is.”
Sexton added that the long incubation period for the virus has also created some confusion about how “asymptomatic” is defined. According to the CDC, it could take up to 14 days after exposure for someone to show any symptoms.
“There are people who are positive but really have no symptoms, and there are people who develop very mild or atypical symptoms, and then there are people who think they are asymptomatic until I ask them about some of the more unusual manifestations of COVID-19.” she said. “But sometimes all of these are grouped together as ‘asymptomatic.'”
People in all three categories, including presymptomatic ones, are believed to be able to transmit the virus, although there was again some confusion about the nature of the asymptomatic spread. In early June, the World Health Organization was forced to clarify that the coronavirus can be transmitted by people without symptoms after one of the agency’s leading infectious disease epidemiologists, Dr. Maria Van Kerkhove, stated that thought the asymptomatic spread of COVID-19 was “very rare.”
Van Kerkhove’s assessment was roundly criticized by scientists around the world. A day later, he explained that his response was based on several studies that had not been subjected to a peer review and made it clear that the WHO guidance remains in effect.
However, even if scientists are confident that asymptomatic people can be called silent spreaders, transmitting COVID-19 even if they show no symptoms, it is unknown to what extent these people are contributing to the outbreaks.
“Until now it has been very difficult to determine how much transmission is due to asymptomatic people and how much is due to people who become quite ill,” Sexton said.
Another big question is how the immune systems of asymptomatic people respond to the coronavirus and whether they will develop antibodies or other protections against the virus.
A study published June 18 in the journal Nature Medicine was the first to examine immune responses in asymptomatic patients with coronavirus. The researchers followed 37 asymptomatic people in Wanzhou Chinese District and compared them to 37 people with symptoms.
Although it was a small study, the scientists found that asymptomatic patients developed antibodies, which are protective proteins produced by the immune system in response to an infection. But the researchers found that the antibody levels among these individuals decreased in two to three months.
It is not yet known whether COVID-19 antibodies confer some kind of immunity, but if they do, recent results suggest that those protections may not last long, especially among those who are asymptomatic.
Mercado said it is possible that even low antibody levels may provide some protection, although more study is needed to know for sure.
“There is a ray of hope that an antibody response can at least decrease the chances that it will progress to serious illness,” he said.
Dr. Daniel Kuritzkes, chief of the Division of Infectious Diseases at Brigham and Women’s Hospital in Boston, said it is not entirely surprising that asymptomatic patients have a more modest immune response. But, he noted an intriguing finding from the Nature Medicine study that further blurs the definition of “asymptomatic” coronavirus patients.
In the CT scans of all study participants, the researchers found signs of lung inflammation, known as lung infiltrates, even in people who showed no symptoms. According to Kuritzkes, inflammation signatures were seen in 57 percent of the asymptomatic group, a “surprising” finding because CT scans are uncommon in people who don’t show symptoms of a respiratory infection.
“It makes you wonder if they really were asymptomatic, because they clearly had some pneumonia,” he said. “It just shows that the absence of symptoms is not the absence of infection.”
Sexton said the recent study, while small, reveals some insights into the immune responses of asymptomatic patients, but the results also show how much is unknown about this population.
“Until we know what transmission asymptomatic people are responsible for, it makes perfect sense to keep insisting that everyone should wear a mask,” he said. “If you fall into that category and wear a mask, that will prevent you from infecting people and eliminating those viral particles in the environment. And everyone who wears a mask is doing the same for you. “
