A clever way has been worked out to make a vaccine, that uses a live virus, safer but without compromising on its effectiveness;
“...The researchers created a SMART vaccinia virus that replicates normally to induce protection, but can be turned off in response to antibiotics if the person who has been vaccinated develops complications that are serious enough to require intervention. "We basically made the virus susceptible to antibiotics," says Verardi. ...”
-this basic principle can be applied to other vaccines, that uses a live virus, known to sometimes cause serious complications in some vaccinated people thus making them much safer.