The Health 202: Coronavirus keeps spreading. But at least we’ve learned more about it.

Coronavirus: FI Strategy to Stop the Spread

Coronavirus infections are swelling in the United States, which hit 5 million cases over the weekend.

But so is the body of research on how the novel coronavirus spreads and affects people.

Dozens of studies have now been published in top medical journals, providing critical information to public health officials and medical professionals attempting to get a handle on the virus. More understanding of the virus is critical, as its aggressive spread around the country confounds President Trump’s efforts toward an economic rebound and threatens to keep schools and workplaces shuttered through the fall.

There’s a lot left to learn. But some of the blanks are starting to be filled in, now that researchers around the world have had six months to study it (check out The Post’s database of questions and answers about the pandemic).

Here are some things we learned about the virus over the summer — and some questions that persist:


Can asymptomatic people spread the virus?

Researchers are still trying to discover whether people without visible symptoms spread the virus at similar rates as those with symptoms. There’s been a considerable amount of confusion around this question, particularly after the World Health Organization appeared to suggest the virus isn’t spread asymptomatically — and then walked back its pronouncement the next day.

It seems clear that asymptomatic transmission does occur. People with no symptoms carry the same level of virus in their nose, throat and lungs as those with symptoms, according to a South Korean study of 303 people published last week in JAMA Internal Medicine.

The study was the first to distinguish between patients who didn’t develop symptoms initially and those who did develop symptoms later on — which can cause some confusion when looking at asymptomatic spread. Based on their observations, the researchers estimated that 30 percent of infected people never develop symptoms.

Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said last week he thinks the figure is closer to 40 percent.

“The good news about covid-19 is that about 40 percent of the population have no symptoms when they get infected,” Fauci said, but he added that asymptomatic people “are propagating the outbreak, which means that you’re going to infect someone, who will infect someone, who then will have a serious consequence.”

Are some people immune to the virus without ever getting it?

There is some very early, tentative evidence suggesting a segment of the world’s population may have partial protection thanks to the immune system’s “memory” T cells, which are trained to recognize specific invaders.

People may derive this protection from standard childhood vaccinations or from previous infections by other coronaviruses, such as those that cause the common cold, my colleague Ariana Eunjung Cha reported.

“This might potentially explain why some people seem to fend off the virus and may be less susceptible to becoming severely ill,” National Institutes of Health Director Francis Collins remarked in a blog post last week.

“On a population level, such findings, if validated, could be far-reaching,” Ariana wrote. “ … In communities in Boston, Barcelona, Wuhan and other major cities, the proportion of people estimated to have antibodies and therefore presumably be immune has mostly been in the single digits. But if others had partial protection from T cells, that would raise a community’s immunity level much higher.”


How many untested Americans have already had the virus?

The head of the Centers for Disease Control and Prevention estimated in June that there were roughly 10 times more coronavirus infections in the United States than had been confirmed through testing.

There were just 2.4 million confirmed cases when CDC Director Robert Redfield made that estimate — which, if accurate, would have translated to 24 million cases at the time. Confirmed cases have since doubled, to more than 5 million — meaning the virus may have swept through tens of millions of people.

Redfield based his estimate on the results of antibody tests, which examine a person’s blood for indicators that the body fought off an infection, Lena H. Sun and Joel Achenbach wrote.


How does the virus travel?

Scientists initially thought the virus easily spread on surfaces, similar to how other viruses operate. That’s why much of the initial public health advice centered around hand-washing and disinfecting surfaces.

Now public health experts think SARS-CoV-2 is primarily spread through person-to-person contact.

In May, the CDC updated guidance on its “How COVID-19 Spreads” website to say that “the virus spreads easily between people.” The agency also acknowledged the virus may spread other ways, such as through touching contaminated objects or surfaces, but clarified “this is not thought to be the main way the virus spreads.”

“The virus travels through the droplets a person produces when talking or coughing,” Ben Guarino and Joel wrote. “An individual does not need to feel sick or show symptoms to spread the submicroscopic virus. Close contact means within about six feet, the distance at which a sneeze flings heavy droplets. Example after example have shown the microbe’s affinity for density. The virus has spread easily in nursing homes, prisons, cruise ships and meatpacking plants — places where many people are living or working in proximity.”


Do children spread it?

Children only rarely get seriously ill or die of covid-19, the disease the virus causes; data on hospitalizations and deaths make that clear. But whether — and to what extent — they can spread the virus to others asymptomatically is still murky.

Studies are also conflicting on whether the age of children affects their likelihood of spreading the virus. One study conducted at a Chicago hospital found children younger than 5 with mild to moderate cases of covid-19 had much higher levels of virus in their noses than older children and adults — suggesting they could be more infectious, Ariana, Haisten Willis and Chelsea Janes reported.

But a study out of South Korea examining household transmission seemed to reach an opposite conclusion. It found children under age 10 did not appear to pass on the virus readily, while those between 10 and 19 appeared to transmit the virus almost as much as adults did, my colleagues wrote.


Which organs does Covid-19 attack?

The lungs appear most susceptible to the virus. Researchers have also found the pathogen in parts of the brain, kidneys, liver, gastrointestinal tract, spleen and in the endothelial cells that line blood vessels, along with widespread clotting in many organsAriana and Lenny Bernstein reported.

But researchers have been surprised to discover little inflammation on the brain, despite previous reports about neurological symptoms related to the coronavirus. The same goes for the heart. While physicians warned for months about a cardiac complication they suspected was myocarditis, autopsy investigators found no evidence of the condition.


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