The number of people in the study is too small to really make much in the way of definitive conclusions. But it is certainly enough that a larger study should occur.

In the meantime, since vitamins are cheap and not dangerous at these doses, it seems a reasonable measure to go ahead and take them. They might help, there's weak evidence to suggest that they might, and they shouldn't hurt. However, it's important not to overdose. I know that at least vitamin D is dangerous if overdosed. Most people as they get older are low in vitamin D anyway.

In my mind this is something like masks were months ago. Maybe they help, maybe they don't, but the risk of wearing a mask or taking vitamins is pretty negligible, and there are common-sense reasons to believe they might be helpful. Until better experimental results are available, you should use common sense approaches to reduce your risks. They might not work, but the harm of doing them is negligible.