The Centers for Disease Control and Prevention has reported new findings on COVID that comes as Americans are contemplating holiday gatherings celebrated virtually or socially distant with face coverings.

We already know that being inside can increase the possibility of coronavirus transmission because of the virus’s ability to linger—and concentrate—in the air, especially in spaces that are not well-ventilated.

The CDC had said that for individuals to get infected they need to be in contact for, on average, 15 minutes within six feet of someone who is positive for COVID. That’s because experts believe that people need to be exposed to a certain level of virus—a so-called “infectious dose” of virus—before they’re infected.

The CDC is now saying that they’ve documented a case in which infection occurred without 15 minutes of straight contact. In this case, transmission occurred over multiple brief encounters. The person who got infected was wearing a mask but was around a mixed group, with some wearing masks and others not.

Transmission indoors can be influenced by a number of factors: how good the ventilation is, how infectious the person is, how easily the virus moves through a particular space and whether or not masks are being worn.