The vaccination felt like most others — a slight pinprick in M.'s  upper arm, followed by the application of a Band-Aid and advice to monitor the injection site for any unusual reactions.

The vaccine, however, is unlike any other. It's not meant to protect against the coronavirus, or any germ, for that matter. 

It is meant to protect against a deadly opioid overdose.

When M. (who requested that her full name not be used to protect her identity) got the shot this Tuesday, she became just the sixth person to receive it.

"It's very powerful now that I think about it," she said of participating in the trial, just a few hours after getting the vaccine.