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