Now we have a clearer picture of how COVID-19 enters our body.
What's been defined so far, is the "mechanism" of the infection.
The spike proteins of the coronavirus, bind to the receptor proteins on the surface of cells, to pierce into them.
Only cells with ACE-2, TMPRSS2, or Furin receptors can get infected.
But it has been hard to identify exactly where in the respiratory system, the infection begins, because by the time patients test positive, it's usually passed that stage.
But South Korean researchers from the Institute for Basic Science and Jeonbuk National University Hospital, have managed to capture the very first stage, of the infection.
And they found, the primary targets are "nasal ciliated cells".
Key COVID-19 receptors are concentrated in that confined part of nose, and are not detected elsewhere, not even in the mouth.
So that makes the nose the main gate for the virus to enter our body.
"This scientifically proves, how face masks can actually protect us from COVID-19.
But more importantly, why it is necessary to wear masks properly over your nose.
If you wear it like this, you can still,get infected."
The researchers also found,the nasal cells provide the only place for the virus to replicate during the first stage of infection.
This gives important clues for developing even more effective vaccines.
"Current COVID-19 vaccines are designed to prevent severe illness.
But now we know where the infection starts, we can develop vaccines that can more precisely prevent the primary stage of infection and stop the virus from spreading further."
The researchers say, those vaccines, if developed,can have a synergy when used with current vaccines.
Lee Kyung-eun, Arirang News.