The Delta variant is a viral mutation of COVID-19 that causes more infections and spreads faster than early forms of SARS-CoV-2. What is known for now is that it is more than 2x more contagious than earlier variations, that it may cause more severe sickness in unvaccinated persons, and that even fully vaccinated people with Delta variant breakthrough COVID-19 infections can transfer the virus to others. Vaccinated people, however, appear to be sick and infectious for a shorter amount of time.