The third one.
Do Vampire-Like Proteins Make Coronavirus More Contagious?
The virus causing the ongoing COVID-19 pandemic, SARS-CoV-2, has spread far more quickly than any other coronavirus in recorded history. Why is it so contagious? One possibility is that its spike protein is better at breaking into human cells because it contains a part that resembles a proteinaceous infectious particle, or ‘prion‘.
https://www.forbes.com/sites/jvchamary/2020/04/17/prion-like-coronavirus/amp/