Biden to announce 'historic partnership': Merck will help make Johnson & Johnson coronavirus vaccine

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19. In general, there is pre-set criteria for efficacy of vaccines

and that is at least 50% effective. COVID-19 vaccine guidance (FDA PDF).

The FDA's cutoff for Covid-19 vaccine effectiveness is 50 percent. What does that mean?
No vaccine is 100 percent effective, but some work better than others.

Nov. 3, 2020, 4:58 AM EST
By Jacqueline Stenson

Over the summer, the Food and Drug Administration announced that in order for an experimental Covid-19 vaccine to get the green light, it would need to be safe and “prevent disease or decrease its severity in at least 50 percent of people who are vaccinated.”

In fact, no vaccine is 100 percent effective, but some work better than others. One of the most successful is the measles vaccine — two doses are 97 percent effective in preventing the disease, according to the Centers for Disease Control and Prevention. Still, 50 percent sounds like a far cry from 97 percent.

“I know that 50 percent does sound low but that is still some protection, and some protection is better than no protection,” said Dr. Jeff Kwong, professor of public health and family medicine and interim director of the Centre for Vaccine Preventable Diseases at the University of Toronto.

Based on the effectiveness threshold the FDA has set for a Covid-19 vaccine to be approved or granted emergency use authorization, it’s possible a vaccine becomes available that helps only half of people receiving it, while offering no benefit to the other half. It’s also possible that a vaccine could have different effects in different people – helping to prevent disease in some people while reducing the severity of Covid-19 in others.

https://www.nbcnews.com/health/health-news/fda-s-cutoff-covid-19-vaccine-effectiveness-50-percent-what-n1245506

Even with the annual flu vaccine(s), you are lucky to get 50 - 60% effectiveness if they can target the right ones that will end up in circulation here in the northern/western hemisphere.

Here is the general process for vaccine development - https://www.fda.gov/vaccines-blood-biologics/development-approval-process-cber/vaccine-development-101