Why do some people get sick?

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Months in the event of a pandemic, which has caused more than 500,000 deaths worldwide, scientists are still trying to answer crucial questions about the coronavirus.

Chief among them: all that concerns asymptomatic patients.

One of the most confounding factors in the public health emergency was people who contracted COVID-19 but were not sick and had no symptoms. The United States has more than 2.5 million confirmed coronavirus cases, but it is likely that many asymptomatic people have fallen through the cracks in the official account.

Now scientists say that without a better understanding of how many asymptomatic people have been infected, it is difficult to know precisely how they contribute to the spread of the virus, and whether they have developed antibodies or other protections that would confer some type of immunity against reinfection.

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Dr. Jorge Mercado, a pulmonologist and physician care critic at New York Langone University at Brooklyn Hospital, said that scientists are still not clear why some people who have been exposed to the virus fall very sick, while others develop no symptoms.

“We really don’t know much about this disease,” he says. “We know a little more than we did three months ago, but there are still a lot that we don’t have answers for.

Public health officials are struggling to get a handle on the actual number of people who have been infected. The Centers for Disease Control and Prevention said Thursday that the number of COVID-19 cases in the US – including those that are asymptomatic – may be 10 times higher than what has been reported, which means the real number of cases could be closer to $ 23 million.

“Our best estimate is that, currently, for each case, that the reported, that there are 10 other infections,” Dr. Robert Redfield, director of the CDC, said Thursday.

From the start, many asymptomatic cases went unnoticed because states faced severe shortages of test kits and supplies, which limited the ability to analyze only the sickest patients. Many asymptomatic people probably had no idea that they were still positive, said Dr. Marybeth Sexton, an assistant professor of medicine at Emory University in Atlanta.

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“We tend to pick up asymptomatic or slightly symptomatic people when we do contact tracing, so that when we get someone who is positive and we start testing people they have been in contact with , ” she says. “I think it will be a long time before we know for sure what the real percentage is.” “

He added that the long incubation virus has also led to some confusion over how “asymptomatic” is defined. According to the CDC, it could take up to 14 days after exposure for someone to show no symptoms.

“There are people who are positive, but really have no symptoms, and there are people who are going to develop very mild or atypical symptoms, and then there are people who think they are asymptomatic up to “Ask you about some of the rarest manifestations of COVID-19,” she said. ‘But sometimes these all come together as’ asymptomatic.’ “

It is believed that people in three categories, including those who are presymptomatic – can transmit the virus, although there was still some confusion about the nature of asymptomatic spread. In early June, the World Health Organization was forced to specify that coronavirus can be spread by people without symptoms, according to one of the top infectious disease epidemiologists agency, Maria Van Kerkhove said she thought asymptomatic spread of COVID-19 was “very rare. “

Van Kerkhove’s assessment has been widely criticized by scientists around the world. A day later, she said her response was based on several studies that had not been peer reviewed, and clarified that the WHO recommendations are still standing.

Yet even if scientists are sure that asymptomatic people can be said to be silent spreaders of COVID-19 transmission even if they don’t have symptoms, he doesn’t know how much they are contributing to the epidemic.

“It has been very difficult so far to pinpoint how much transmission is due to asymptomatic and how bad it is because of people who get sick enough,” He said.

The other big unknown is how asymptomatic people’s immune systems respond and whether they will develop antibodies or other protective measures against the virus.

A study published June 18 in the journal Nature Medicine was the first to examine the immune responses in asymptomatic coronavirus patients. Researchers followed 37 asymptomatic people in China’s Wanzhou district and compared to 37 people who have symptoms.

Although it was a small study, the scientists found that asymptomatic patients developed antibodies, protective proteins in the immune system produced in response to infections. But the researchers found that the antibody levels in people decreased within two to three months.

It is not yet known if COVID-19 antibodies confer any type of immunity, but if they do, recent results suggest that protections may not last long – especially among those who are asymptomatic.

Mercado says it is possible that even low levels of antibodies could offer some protection, although more studies are needed to know for sure.

“There is a glimmer of hope that an antibody response can at the very least reduce the chances that you will progress to a serious illness,” he said.

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Dr. Daniel Kuritzkes, head of the infectious disease division at Brigham and women’s Hospital in Boston, said it is not at all surprising that asymptomatic patients would have more modest immune responses. But he noted an interesting finding, by the nature of the study’s medicine, that more blurs the definition of “asymptomatic” coronavirus patients.

In CT scans of all study participants, the researchers found signs of lung inflammation, known as pulmonary infiltrates, even in people with symptoms. Signatures of inflammation were seen in 57% for the asymptomatic group, a “surprising” finding because it is not common to perform CT scans on people who are not showing symptoms of a respiratory infection , Kuritzkes said.

“You have to wonder if they were really asymptomatic, because clearly, they had pneumonia,” he said. “It just goes to show that the absence of symptoms is not the absence of infection. “

Sexton said that the recent study, while small, reveals a glimpse of the immune response in asymptomatic patients, but that the results also show how much remains unknown about this population.

“Until we know how much asymptomatic transmission people are responsible for, it’s an incredible amount of sense to keep pointing out that everyone should wear a mask,” she said. “If you happen to be in this category and you wear a mask, that will keep you from infecting people and putting these viral particles in the environment. And everyone wearing a mask is doing the same for you. “

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