Question

Why is it difficult to make vaccines for viruses? All known viruses must be tested against new vaccines.
Vaccines are very small so it is difficult to determine if the molecule fits.
All known vaccine molecules must be tested to find the right one.
Viruses mutate to attack the vaccine molecules so new ones must be continually produced​

Answer 1

Viruses mutate to attack the vaccine molecules so new ones must be continually produced​ is why it's difficult to make for them.

What is a Vaccine?

This is defined as a  biological preparation that provides active acquired immunity to a particular infectious disease.

Viruses mutate and attack the vaccine molecules and continue its replication process which is why it's difficult to make vaccines for them.

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