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Vexing questions about COVID-19 scientists still can't answer


While scientists and physicians are learning more about the novel coronavirus every day, there is still much that we don’t know about the pandemic.


We compiled several of the murkier questions about the disease with the intention of updating them when more data become available.

Can you get COVID-19 twice or are you immune for life after recovering?

"We really  don't know."


There have been few, unsubstantiated accounts of individuals in Japan and China testing positive for SARS-CoV-2 after fully recovering from COVID-19, but the science is still uncertain.


“There is some anecdotal evidence of reinfections, but we really don’t know,” Ira Longini at the University of Florida told New Scientist.

It may be that the tests those patients were given were faulty. However, if people do not develop immunity, then we all could be reinfected until an effective vaccine becomes available.


How long can you be infected yet show no symptoms? And if you are asymptomatic, how long are you contagious?


Unknown. One analysis of the Diamond Princess cruise ship outbreak showed that nearly a third of the 104 infected passengers remained asymptomatic even after an average of 10 days of observation at the Self-Defense Forces Central Hospital in Japan.


If you are asymptomatic, then you are contagious for a period of time, but how long is not known. The kind of testing to screen for asymptomatic infections is not yet available, according to the Guardian.


What percentage of carriers are asymptomatic?


Unknown. The data aren't clear, but a study in Iceland found that 50 percent were asymptomatic.


If you have a mild infection, you can test positive by throat swabs for days and even weeks after being ill. When is it safe to be around others?

Unclear. But one study that has not been peer-reviewed suggests that those who were only mildly sick can’t infect others by about 10 days after first getting symptoms, according to the medical journal Stat.


Is there any way to know whether someone has had COVID-19 in the past?


Not yet. However, antibody tests to check for a prior infection are reportedly under development.


Can the new coronavirus linger in the air for hours?


Plausible, but likely very rare: Coronaviruses are generally thought to be spread from person to person through respiratory droplets, according to the CDC. However, a recent National Institutes of Health study found that under lab conditions, SARS CoV-2 — the virus that causes COVID-19 — can exist in an aerosolized form. (The pathogen becomes suspended in a gas.) Under such limited conditions, it has a half-life of 2.64 hours in still air, meaning half the virus' particles have become inactive after that amount of time, and half of what remains become inactive after another 2.64 hours. After 24 hours, only a tiny fraction of the original, potentially active particles would survive.

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