To be honest this is just really basic and normal medical science. Our natural immune system confers varying degrees of protection against even variants. Now we are supposed to be shocked. This is the extent of mainstream media reality distortion.
And they keep making a huge terrifying thing out of FLU. Flu always killed many vulnerable elderly and weakened people every year.
I agree with that to a point, but ...
Were the people who recovered from COVID "less likely than vaccinated to get infected during Delta wave" because they were already infected?
Or, perhaps, they are less susceptible to COVID due to their individual genetic and immunity profiles, making them capable of fighting off ALL variants?
Having COVID before may not be the complete cause of their resistance to COVID, but it might possibly be evidence of a natural ability to fight the virus without prior infection or vaccinations.
Just as there are immuno-compromised people in the population, it's reasonable to assume there are also people with exceptionally strong immunity responses. in every pandemic or epidemic, there have been survivors who were able to contract and survive the disease that may have killed millions of others.
I get that the article is trying to draw a comparison between the vaccine and natural immunity, with the implication that vaccines are lacking in their supposed ability to increase immunity response. But, we need to also recognize that a vaccine in a specific person with already low immunity to COVID won't be as effective as the vaccine in someone with very high immunity capabilities able to fight the virus without the vaccine.