minor impacts but agravate injury in [some|many|most|all] major
impacts'.

The only reports on it I've seen said it was likely to happen in only a
very few cases.

It also said that a major impact was not needed for injury to occur, as
even minor impacts could cause the effect (but presumably were less likely
to injure).

On the other hand, it also said that serious brain damage/death only
hapened in a very few cases.

But it went on to say that as rotational thingummies are more likely to
cause severe brain damage/death, then it's likely to be over-represented in
the more serious cases.

So yeah, more research needed!