dissecting the medical names into numbers & looking at table of elements, clues into the nature or essence of it.

(H7N9) = (11) = (2)
(A/H7N9) = (12) = (3)
(A=Avian) = (1)

COVID-19 = (9)

C 3
O 15
V 22
I 9
D 4

3+15+22+9+4=53=8
3+1+5+2+2+9+4=26=8
3+6+4+9+4=26=8

8+19=27=9
8+1+9=18=9
8+10=18=9
8+1+0=9

(H7N9) = (11) = (2)
COVID-19 = (9)

9+2=11
11=K

..

Oxygen is the chemical element with the symbol O and atomic number 8

Fluorine is a chemical element with the symbol F and atomic number 9.

Sodium is a chemical element with the symbol Na (natrium) and atomic number 11

by using the number value of both names broken down threw sum addition.
(A=1) (1+1=2)

COVID-19 = (9)
H7N9 = (11)

matching the numbers 9 & 11 into the table of elements & matched them to..

Fluorine=(9) & Sodium=(11).
..

Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water.

It is used to make most fluorine-containing compounds; including the commonly used pharmaceutical antidepressant medication fluoxetine (Prozac) and the material PTFE (Teflon).

https://en.m.wikipedia.org/wiki/Fluorine

https://en.m.wikipedia.org/wiki/Hydrogen_fluoride

https://en.m.wikipedia.org/wiki/Hydrofluoric_acid

https://en.m.wikipedia.org/wiki/Fluoroantimonic_acid

https://en.m.wikipedia.org/wiki/Electronegativity

https://en.m.wikipedia.org/wiki/E_number#