5 things we still don't know about COVID-19

Scientists have already learned an extraordinary amount about COVID-19 in the one year since its emergence, but there's still a lot we don't know.

"In terms of understanding anything in any real detail, we've got miles and miles to go," Maureen Ferran, PhD, an associate professor of biology at Rochester (N.Y.) Institute of Technology, told CNN. "This is going to keep virologists and public health officials busy for decades."

Below are five questions about COVID-19 that the world still doesn't have the answers to: 

What is the origin of the virus?

  • Initially, the virus was thought to be tied to a Wuhan, China, market selling live animals, but a Lancet study found a third of initial patients had no direct link to the market.
  • Scientists believe the virus likely originated in the wild.
  • Studies have found evidence that the virus may have been circulating in the U.S. and Europe in December 2019, months earlier than initially thought. 
  • The World Health Organization is investigating whether the virus could have been circulating before the first cases were identified in China in December.  

Why does it affect some people more than others?

  • First identified as a respiratory illness, COVID-19 is now known to prompt a range of symptoms and complications. Scientists don't know how long these effects last.
  • Children tend to have less serious COVID-19 infections because they have fewer ACE2 receptors in their noses, which are how the virus gets into our cells. However, scientists don't yet understand why older people have such a high COVID-19 death rate, or why the virus affects some people so much more than others.

How is the virus spread?

  • The virus is spread via human transmission, but there's debate over how exactly that happens.
  • Scientists say the key way the virus is spreading is via droplets, which are sent into the air when someone coughs or sneezes, and masks can help prevent their spread.
  • Some scientists believe the virus is also spread by aerosols, much smaller particles that can stay suspended in the air for hours and travel long distances. Cloth masks can't protect against aerosol transmission. 
  • It's also unclear what amount of the virus is needed for someone to get infected.  

How long is someone who survived COVID-19 immune to the virus?

  • While it is possible to get infected twice, it is very rare at least six months after someone is infected. 
  • Scientists don't know how long natural immunity from the virus lasts because the virus hasn't been with us for long enough.
  • Though scientists are optimistic about the vaccine, they don't know whether the virus will mutate in a way that will render a vaccine ineffective. The longer it takes to vaccinate large swaths of the population, the more opportunity it has to mutate.  

When will the pandemic be over? 

  • It will likely take years to vaccinate most of the world's population — something that is necessary to stop the spread — and polls show that some people aren't willing to get the vaccine. 
  • A vaccine still doesn't offer guaranteed protection. Even if someone is vaccinated, scientists don't yet know whether it's possible they could get the virus and spread it, even if they don't get sick.
  • The virus could mutate and become less deadly or infectious, but it could also become more virulent.  

More articles on public health:
Number of COVID-19 hospitalizations, state by state
US flu activity still unusually low: 6 notes from CDC's FluView report
Number of people willing to get COVID-19 vaccine rising, surveys find


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