Don’t even have to bring anything, early smallpox vaccines were little more than ground up pox sores rubbed into a cut. But it worked a hell of a lot better than no vaccine.
Noticing the connection between cowpox and smallpox helped develop a safer vaccine, but prior to that in China and India they invented variolation (grinding up and applying the scabs to cause a milder infection) centuries before European vaccination experiments: https://en.wikipedia.org/wiki/Variolation