Two common respiratory viruses can fuse to form a hybrid virus capable of evading the human immune system and infecting lung cells.

Most vaccines are designed to provide immunity against just one pathogen. Vaccines for chicken pox (caused by varicella-zoster virus) were only developed to fight that one disease, for example.

Questions over the origins of the virus that sparked the Covid-19 pandemic have resurfaced a debate over a controversial type of research that can involve altering the genetic information of viruses.