We're now seeing a plethora of additional data showing that the Pfizer/BioNTech COVID vaccine "booster" restores the somewhat waning immunity/protection seen 5-6+ months after the first two doses were given to beyond the original protection levels for the 2-dose sequence. At this point, it's becoming pretty clear that being "boosted" should now simply be called "fully vaccinated."
While it was not a given that protection from the original 2-dose regimen would wane, many thought it might, since that is the case for a host of other viral diseases (tetanus, diptheria, polio, etc.) and vaccines which feature a delayed additional dose many months after the initial dose(s), so having a "booster" is commonplace in virology.
If we weren't in the middle of a pandemic that has now killed over 800K Americans (all but 20K unvaccinated) and over 5.2MM worldwide, we would have had the time to learn in longer clinical trials that a 3rd dose was needed, but we know now. That's how science works when new data become available. The other good
Specifically, over the last 2 days studies were published showing that: i) in Israel, deaths were cut by 90% for those (over 800K in the study) over 50 who were 3-dose recipients vs. 2-dose recipients (who are still relatively well-protected from severe illness/death vs. the unvaccinated, but not as well as they were) and ii) the CDC published data from Pfizer's randomized clincal trial of 3 shots vs 2 shots + placebo showing 95% efficacy for preventing symptomatic infections across all age 16+ groups (N=10,125).
In addition, very recent data also came out today from Pfizer from a laboratory study showing that serum samples taken from patients with 3 doses of their vaccine restores full immune system neutralizing antibody levels (to what was seen with 2 doses in previous variants) to the omicron variant, which is also good news. I think it's safe to presume that we'll see similar data for Moderna's mRNA vaccine (and perhaps even better, since theirs "waned' less after 6 months vs. Pfizer's).
Finally, early indications are the immune response suffers less waning than the 2-dose regimen, which is not surprising, given how the immune system often works in a prime-boost scenario as is used in many other vaccines. So it's quite possible the boosters will maintain high levels of neutralizing antibodies and T-cells/B-cells for up to a year or more. However, we simply don't know that to be true yet and we don't know whether omicron will have any impact on that. We should have 1-year data on people who were in the booster trials within several months. Hopefully we won't need annual boosters, but we might and to me given the extraordinary safety profile of these vaccines, that should be a non-issue for most.
First link below is to Dr. Eric Topol's (one of the most respected medical experts in the world, from Scripps) Twitter feed discussing all of these studies, briefly, and the next 4 links are to the relevant source scientific information/papers associated with the work discussed above .
https://twitter.com/EricTopol/status/1468941307166953475
https://www.nejm.org/doi/full/10.1056/NEJMoa2115624
https://www.cdc.gov/.../slides.../02-COVID-Perez-508.pdf
https://www.pfizer.com/.../pfizer-and-biontech-provide...
https://www.nature.com/articles/d41586-021-03592-2