It should reduce the number of flare-ups of type 2, since everyone would be protected again, but you'd also be back to the situation where anyone could be expos

It should reduce the number of flare-ups of type 2, since everyone would be protected again, but you'd also be back to the situation where anyone could be exposed due a vaccine derived case. The goal is to eradicate the disease completely so that the vaccine doesn't need to be used, since it can trigger cases. Going back to the trivalent (ie going back to distributing the type 2 vaccine widely) would be a step back from that goal, albeit maybe a necessary one.