What do you mean with that? Nic the NZer … The 'virus' mutates meaning its specific RNA sequence can change when it reproduces. But hopefully the vacine still works for new mutated virus strains. This doesn't have to be true however. Flu vacines for example don't seem to handle a wide range of flu variants. Andre … There was nothing intended to be about other illnesses in what I wrote. Sacha and Nic both picked up where I explained the control group got something else other than the vaccine that might have more side effects that a pure placebo, which is why I didn't want to use placebo for what was given to the group. But what was given to the control group was different for the different trials. Hence the reason for using the words "something else".