I think the psychological effects of avoiding places where large numbers of people gather will linger for a while. People might not want to go where infections could easily be spread. There's also the impact on the economy to consider. How many days of sick leave/quarantine leave can you take before your wages take a hit? Or your job position entirely? Would you still save up for a holiday next year?Why would 2021 be impacted, out of interest? They think there might be a vaccine by 2021, so the threat of the virus itself would in theory be gone.
Besides, it will take a while to get the vaccine out to everybody and to fully eradicate the disease. I'm not sure if the outbreak will be over (or, a worrying thought, even back to current levels) by this time next year. It usually takes months of clinical studies to get a vaccine approved, and that process can't be rushed without increasing the associated risks. In this case I believe the risk acceptance criteria will be quite a bit higher than usual, but I still don't think there will be a vaccine ready for the general public for quite some time still, even in developed countries.