There is a potential paradox here because of original antigenic sin (from the paper name): basically the vaccines only present one antigen whereas in natural infection there are multiple antigens. Once the immune system learns one it generally doesn’t learn more on the next exposure (actual infection). Combine that with the antigen presented by the vaccine (spike protein) being the more frequently mutating antigen and you can have a scenario exactly like the GP describes.

>This doesn't make any sense; the vaccine confers immunity.

Obviously not look at the virus particles in wastewater (Netherlands) for example : https://coronadashboard.government.nl/landelijk/rioolwater

The Virus seems to stick around in countries with high vax rates and to disappear in countries with very low rates.

Additionally the immune systems of vaccinated individuals display strange behaviour toward tolerating the virus as you can read in the following study:

"the described class switch towards non-inflammatory IgG isotypes, which otherwise rarely occurs after vaccination or viral infection, may have consequences for the choice and timing of vaccination regimens using mRNA vaccines."

https://www.medrxiv.org/content/10.1101/2022.07.05.22277189v....

They may be talking about immunological imprinting[1] - Something possibly resulting in a less than optimal immune response - from the initial vaccine creating highly specific antigens, thus not as comprehensive as an initial natural infection might give to prime the immune system against the virus and its variants. [1] https://en.wikipedia.org//wiki/Original_antigenic_sin