If there is a miracle vaccine ? by the summer and parks can re-open safely and even if it is quite late in the season there might be appetite from the public to go to theme parks even when it is quite cold in November / December completely shifting the season I reckon.
The thing with vaccines is that it's in concept fairly quick to throw them together. I heard somebody in the field say it takes about two weeks to make a simple vaccine if you've got the virus isolated. The problem is testing and validating the vaccine. Both figuring out if it's safe for use and whether it's effective, but also in what doses to administer it, figuring out the potential side effects/complications, and determining which groups it would be safe for. You
really don't want to rush out something that causes birth defects or things like that (or if it does, at least you should document it so pregnant women can be advised not to take it). The trial patients need to be followed up for a long time to see if there are any long-time complications as well, so this is not a process that can be shortened by any meaningful length of time.
So yeah, the two weeks of lab work and chemistry need to be followed up by at least a year of trials. Even if by some outstanding chance they figured out the exact recipe for a perfectly working vaccine on their first try back in February, ensuring that it is working perfectly and determining its correct usage would still take a 1-1.5 years. Only then could they start manufacturing it in large quantities and ship it out, first and foremost to essential healthcare personnel, at-risk groups, other essential personnel, and only
then would it be available to the broader public. That may still be two years away.
On the bright side, however, finding a
treatment for the worst complications of the virus might not take as long. There's a decent chance that some drugs that are already FDA-approved as safe for use could be effective against the virus. What makes SARS-CoV-2 so dangerous is that it spreads quickly, the population doesn't have immunity against it, and there is no treatment. That first bit is why we're in lockdown, the second bit is what a vaccine hopes to address, but if the third bit can be addressed, the first two wouldn't be as critical anymore. Maybe then the lockdown could be eased and the parks could reopen. But I wouldn't bet on it happening at least until summer.