Very likely that by the time a vaccine is ready for clinical use (say, a year, optimistically, going by historical precedent), the virus will probably have already spread enough such that a vaccine will only really be useful for countries that haven't had it.
It will take time to verify the exact way the virus spreads will continue to take a while. If it can be spread before symptoms appear, then that will obviously make it harder to control the spread of it.
Finally, I wouldn't place the blame solely to the anti-China people who have an interest in making it seem like the "sky is falling". Some people want to exaggerate things to advance their own exposure, some people are just a lot more trigger-happy with posting alarming news in general, some people may be genuinely scared and latch onto the most exaggerated news due to fear, and there are some people who are anti-vaxxers, racists, or general trolls as well, all on social media.
Some may be spreading disinformation deliberately, some maybe doing so unknowingly.
