Dear Dr. Roach: My wife and I are both in our late 60s. She has gotten three doses of the Pfizer vaccine, and I have gotten three doses of the Moderna, only because that was what was available when we got our first dose. Because of our age, we are considering getting a second booster dose. I know the recommendation is that either vaccine would be fine, but we’ve heard that since the two vaccines attack the virus differently, it might be a good idea to switch vaccines, so I would get the Pfizer and she would get the Moderna. What are your thoughts?