They are not quacks, they are scientists. Using the scientific method they have taken a theory and tested it. The results have been forwarded for peer review. They have all failed peer review. It is called "The Scientific Method".

It can be quite funny, and scientists find themselves testing very strange theories or ideas. The more bizarre ones are awarded here https://www.improbable.com/ig/winners/

This is good stuff and on occasion something good comes from it - like the guy that looked at the properties of tangled string then came up with a solution to headphone cables. Something we all are grateful for.

So the guys you cited above are not necessarily quacks, they are scientists and they believe that they have discovered something. As yet nobody has been able to recreate the science nor validate the theory. If they do, something will happen, if they don't there is no need.

None of the scientists cited above question the effectiveness of the vaccines themselves by the way, so they are not speaking out against vaccines.

The vaccines work, the three scientists cited above agree.