Answer:
he ability of some viruses to change their genetic material frequently is known as genetic variation or mutation. This process leads to the production of viruses with different protein molecules in their protein wall. The reason why a vaccine that worked against the old virus may not work against the new types is because the vaccine is specifically designed to target and neutralize certain proteins or antigens present on the surface of the old virus.
When a virus mutates and produces new types with different protein molecules, these new types may have altered antigens that are not recognized by the antibodies produced by the immune system in response to the old virus. As a result, the antibodies may not be able to effectively bind to and neutralize the new virus.
To illustrate this, let's imagine that the old virus has protein A on its surface, and the vaccine stimulates the production of antibodies that specifically target protein A. However, if the new types of the virus mutate and now have protein B on their surface, the antibodies produced by the vaccine will not recognize protein B. This means that the new types of the virus can still infect cells and cause illness, despite the presence of antibodies produced by the previous vaccine.
In essence, the genetic variation of viruses can lead to the production of new types with different antigens, making them resistant to the antibodies produced by a previous vaccine. This is why scientists and researchers continuously monitor viral mutations and develop updated vaccines to effectively target and neutralize these new types.