I think @blm1007blm1007 and Sue have provided reasonable explanations for MD’s advice. The MD could have misspoken or the OP is severely immunocompromised (“no antibodies” was mentioned” and the MD may think an exception is appropriate. If I were patient, I’d ask why he thinks I’d be exception to guideline.
My pulmonologist makes thoughtful and deliberate decisions and welcomes discussion. If he told me, after I questioned it, that he thought I needed another, I’d follow his advice. If my young PMD (or first pulmonologist) suggested it, I’d be reluctant,