.... unless of course the advice comes from.. you know... a doctor.
I see my specific post got removed and I suppose I should have been more general, so I'll just say this:
Immunocompromised patients are at higher risk for serious complications from COVID infection even with full vaccination.
Johnson and Johnsons vaccine, while still highly effective, was never as effective as either of the mRNA vaccines(Pfizer and Moderna). Boosters have now been recommended for both of these vaccines for immunocompromised patients, but as of yet no recommendation has been made about J/J.
Hypothetically, if I had an immunocompromised patient who had been immunized with a J/J vaccine, I would believe them to be inadequately protected. Since J/J is both in short supply and has not been recommended for a booster, that patients options would be either remain as they are and hope for the best, or start a new vaccination series with either Pfizer or Moderna. Since the vaccines dont elicit exactly the same response, a single dose of Pfizer or Moderna would not count as a "booster" to the original J/J shot and so would still need to be followed by a second injection of the same vaccine at the appropriate interval.
Please note the above is for educational and informational purposes and is intended only as something to consider discussing with your own personal physician.