It looks like I have to respond to your comment.
There many scientific journals, but not all are good. The same goes for scientists. There is no requirement that any scientific paper be significant or worthwhile. Most papers, even if the work was done well, don't stand the test of time.
The potential problems of PNAS publications, has been well known among scientists for many years. In fairness, there are many good papers printed in PNAS, and the reputations of most members of the US National Academy of Science are excellent. Some journals have continuing reputations that hold up over the years. I can mention Nature, Science, among others.
However, there are many so-called scientific journals that will publish pretty much anything that's neatly typed. Any grad student in the sciences, has to learn which journals are worth reading and which journals publish less interesting papers, or even junk. In any given field, there is a pecking order of these journals. Every field has one or two journals that are considered as the trusted journal of record by most of the scientists in that field.
That's one reason why changing fields of research is difficult. One has to learn all over again, which journals and which scientists are good, and which are filler, or worse. As a grad student, I learned to regularly read Nature (there is now a whole series of Nature journals), Science, PNAS, The Journal of Biological Chemistry, Biochemistry, and The Journal of Bacteriology. Later in my career, I switched to cancer research, and I had to learn, all over again, which journals to trust. That process was much faster the second time around.
In addition, over the years there has been great proliferation of journals. Some newer ones are excellent, and others are junk. In cancer research, I have seen some so-called journals that publish stolen work without any effort to identify obvious plagiarism. The entire paper was copied word-for-word including all the figures and tables, by some Chinese authors, from a paper published a year and a half earlier! (To be fair, I also know of Chinese authors who regularly publish excellent work.) As a result, a reader always has to develop an eye for what seems good and what seems like junk. This why I am so wary of non-scientists who read scientific literature but jump to wrong conclusions.
This is also why you should be wary of my own words here on AH in regards to Covid-19. I know biological chemistry, molecular biology, cancer basic research, and cancer clinical research. Other the years, I've developed a good working knowledge of immunology, as it applies to cancer. However, I've never cut my teeth on infectious diseases, their treatment or their prevention. I've never tried to hide that. You may have noticed that whenever TLS Guy speaks about clinical aspects of treating Covid-19, I nod to him. This is all part of a good scientific education – you must learn to recognize what you know – what you don't know – and you must never ever fool yourself.
Sorry for the long-winded rant, but you touched a nerve. [//END RANT]
