It originally had a higher rate of side effects than many other vaccines because it was a locally replicating live virus. This is why vaccinated people typicall

It originally had a higher rate of side effects than many other vaccines because it was a locally replicating live virus. This is why vaccinated people typically have scars because it would create a local infection and a lesion on the arm. In some rare cases this would go systemic and result in a full scale infection, so when it was locally eradicated the mass vaccination program ended in the US (1972). Apparently the modern vaccine uses an attenuated virus so it’s less likely to cause issues. I assume that’s what is used if you elect to take it for travel in Switzerland.