Question: Surely if you inserted a virus into someone it would make their condition worse? They would not be able to use simple antibiotics as viruses reproduce in cells.

Louisa Chard answered on 18 Jun 2010:

You are right that they would not be able to use antibiotics. They do not work for viral infections at all, but many people get this confused and want to be prescribed antibiotics for viral infections so I’m really pleased when I hear that people are aware of the differences between viral and bacterial infections. However, the viruses that we use only produce mild infections like colds at the most, some no symptoms at all and the persons immune system can quite easily clear the virus after a few days so it can’t do much damage. All the the viruses we use have already been used and licenced in humans (one is licenced for cancer treatment already and one was used as a vaccine for smallpox eradication) so they are considered safe for use, even in people who are unwell. When we make new viruses as cancer treatment we need to get a good balance between safety and efficacy (how well it works) and this is tested extensively in the lab.