In this specific case boosters are likely unnecessary because pancreatic cancer isn’t contagious and if it works all the persons current cancer cells are dead.

As to the need for boosters, it’s more a question what benefit a booster provides vs its risks and costs. Frequent measles boosters aren’t recommended in the US in large part because the disease is already rare here. COVID is however still very common which changes the exposure risks part of the equation.

This is also why vaccine boosters for measles are recommended when you travel to specific countries. https://wwwnc.cdc.gov/travel/page/travel-vaccines

I'd be fine with spending €100 per year on each of ten vaccines that each need annual boosting, if that reduced by merely 10% my risks from each of the top ten likely causes of death and QALY reduction at whatever my age is in any given year of my life.

This isn't that cheap, not yet at least, but I think "what's the cost?" is a much more important question than "does it need boosters?"

I am not entirely sure why you are getting downvoted. It says right in the study

> Vaccine-expanded T cells were durable, persisting up to 2 years despite post-vaccination mFOLFIRINOX treatment

So yes, that seems to suggest you may have to keep going back every couple years for more boosters.

Covid MRNA vaccines short lived effect was more to do with the characteristics of the virus and the way our immune systems generally function, IMO.