The South African strain shares at least one of these mutations and also appears to be increasing in prevalence there, which is sort of an independent test of the hypothesis, albeit (I think) with weaker data.
So too early to be sure, but good reason to be alarmed and to take action. However, these strains are likely elsewhere already. One hopes that they are at a low enough level that they will not spread, but so far attempts to contain spread have been disastrous in Europe and the US. The quick action to suspend travel now is good, but it doesn't mean much if uncontrolled spread within borders is tolerated. The more people get infected, the more mutations will randomly occur in the virus - and some of them may increase spread, or make it more lethal, or make it harder to defend against with natural immunity or with our present vaccines (only increased spread has been suggested for this new variant, not the other possibilities). Allowing the virus to run free through your population is idiotic for many reasons, it turns out.
EDIT: Going based on prior knowledge, the vaccines *probably* protect against these strains too. But we have no data about this and it's far too early to be confident. Wearing masks and avoiding other people definitely protects you.