Letter: Many challenges in engineering a virus

From Adam Grassly, London, UK

The idea of engineering a benevolent SARS-CoV-2 virus to wipe out an older, more harmful variant is interesting (Letters, 1 January). However, it poses a few challenges.

Engineering a variant that is more transmissible could go hand in hand with improving its ability to invade host cells, with a possible risk of causing a stronger, and more symptomatic, immune response.

Even if engineering a tame and friendly virus were successful, another problem would be genetic mutation. As a virus replicates, mistakes in the genetic code that are favourable are passed on and increase in number. Such mutations could code for a more deadly virus.