evidence: You can pass COVID-19 to someone else both before and while you are sick. Adults may be able to infect others before signs of being sick develop. Most people are contagious five to seven days after becoming sick. Some people pass the virus without feeling sick at all. Young children and people with weakened immune systems may be able to infect others for an even longer time. [...] Being unvaccinated or not being up to date on COVID-19 vaccinations also increases your risk of severe COVID-19 outcomes.