The trials for Pfizer's drug are being given to people with confirmed diagnoses. So the goal is to see if they can develop a drug that's effective as a treatment.

Conversely, the Merck drugs testing is aimed at seeing if they can develop a preventative type of medication. This trial is going to involve people who live with someone who has a lab-confirmed symptomatic case of COVID. And the goal is to determine if the drug has an effect on whether or not people get it at all.