system
Given the following post, respond as if you're commenting on Reddit:
human
Question: fully vaccinated + catch covid19 == booster dose?

Since a few weeks we read about more and more fully vaccinated people catch COVID, often mild cases.  I wonder what effect this has on the immune system of the affected people.  I am specifically thinking about the group of people who become ill enough to notice symptoms and get tested, but not enough to end up needing treatment in a hospital or ICU.  Could the effect in them be similar to a booster shot, or even a variant-specific booster?  Has this been studied already, or are there any studies in progress?
gpt
In theory you're right, exposure to SARS2 is in some ways equivalent to a booster dose. Whatever spike specific T and B cells you had should expand and, if you happened to catch one of the variants, your antibodies will probably adapt to that variant. 

There havent been any studies that ive seen, its too soon really. Right now we are learning that vaccinated people can still catch and spread the virus, and that the infection can be symptomatic. 3-6 months from now we will be able to look at those people and compare their antibody, B and T cells to those of people who got the vaccine but avoided the virus. 

It should be noted that we still dont really know what constitutes "better immunity". High antibody titers seems like it would be good, but there is little indication that antibodies are very important for protection. People who arent able to mount an effective B cell response arent getting more sick, its T cells that are the key.