There are reports Trump is trying to buy exclusive access to a potential coronavirus, probably by buying the German firm (report). As you would expect Germany is resisting. I could see the EU passing a rule unusually quickly to block any such sales of any company to ensure the EU countries get first call on any vaccine produced in the EU.

Come Jan 2021, if not before, that would see the UK excluded from the EU protection and bidding for the vaccine against the economic might of the US and China. According to a leaked report the UK might still be affected by the crisis during the first quarter of 2021. This would certainly fit with reports in early March that the vaccine might take a year to get to market.

No one during "project fear" predicted precisely this, but many predicted the UK being squeezed between the EU and the other big players like the US and China, and that could certainly happen.

If that proved to be true, it could also mean that (in retaliation) the US could put mainland Europe at the back of the queue for any vaccine produced by the US. So, "come January 2021" we could be in a better situation than if we had remained.