This is the big one. Preventing serious illness is obviously great, but without preventing infection/transmission it becomes a bit of a slog. One vaccine is one serious illness or death prevented at best. With this, it has the multiplicitive effect that every vaccination is a chain of transmission broken and a boost on our road to re-emergence
A lot of people assumed this was the case anyway, which is fair enough as it turns out, but having it confirmed is obviously great news.