Several interesting takes on what will happen to vaccine trials once Emergency Use Authorizations (EUA) are given to the first vaccines.
TLDR: The placebo groups may be screwed up thanks to unblinding or volunteers exiting and getting the approved vaccines.
The Vaccine Tightrope
Clinical trial success rates for vaccines against infectious diseases are (according to these estimates) the absolute best in any therapeutic area in the whole industry. Now, that means that a full one-third of those trials are successful, as opposed to about 3% of the oncology trials
We may get into a situation where an interim readout of the data show that a vaccine may well be working, but that granting an immediate EUA has a real danger of blowing the statistics for the complete trial.
Early approval of a COVID-19 vaccine could stymie the hunt for better ones
“What’s really important is that the science does continue,” says Seth Berkley, who helps run the COVID-19 Vaccine Global Access Facility, an international effort to develop and manufacture a portfolio of COVID-19 vaccines. He explains that the world needs multiple vaccines against the pandemic coronavirus. Not only might some work better than others, but factors such as cost or side effects mean some might offer benefits to specific groups, such as the elderly, pregnant women, or those in low-income countries. “Even if multiple ones work, they may have characteristics that are particularly important for one population versus the other,” says Berkley, who also heads the advocacy group Gavi, the Vaccine Alliance.