Health Advice



Should you switch your vaccine brand for a second booster?

By Keith Roach, M.D. on

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? -- T.A.

Answer: It is indeed true that the Moderna and Pfizer vaccines, although very similar, have different effects on the immune system. There are some experts who recommend switching vaccines, just as you've suggested. Both vaccines are excellent at preventing severe disease and at raising antibodies. But the types of antibodies are a little different, and the effects on T-cells, the other main arm of the immune system, are also different. I switched vaccines for my booster. Most of the studies showing benefit have used boosters of the same type as the original series, so that's also a perfectly good option.

Initial studies looking at booster shots that have been optimized for the omicron variant have not shown better outcomes than the original vaccine. So don't wait for a new formulation. All adults who received the Johnson & Johnson vaccine, anyone over 50 and anyone with moderate-to-severe immunocompromise who had their third dose four or more months ago -- those who are in the group recommended for a fourth dose by the Food and Drug Administration -- should consider scheduling. Those at highest risk -- such as older adults (over 75 or in a nursing home), those with diabetes or those with immune deficiency such as organ transplant -- should get a vaccine now.

People who had a recent (within one year) confirmed COVID infection AND three doses of vaccine have a high level of protection and probably do not need a fourth dose.

Dear Dr. Roach: At 82 years old, for the past four or five years, I have been experiencing knee pain when I climb stairs. I have no other issues with my knees. What is your opinion regarding mesenchymal cell injections? I have been overweight all my life. Currently I'm about 25 pounds overweight. -- C.V.G.

Answer: Mesenchymal cells are a type of stem cell, which under different conditions can develop into other types of cells. In theory, when injected in the knee, they can act to repair cartilage damage associated with osteoarthritis, the most common (but by no means the only) cause of chronic knee pain in an older adult.

There is not enough evidence to support the use of stem cell injection for knee arthritis. A recent trial following three individuals for five years after injection showed improvement at six months, then a steady deterioration, but still improved compared with pretreatment. Much larger trials are necessary before I could recommend this treatment. It is still considered experimental and you would have to pay out of pocket, outside a clinical trial.


Although it's not easy, losing only a few pounds can certainly improve symptoms, without any other treatment.


Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to or send mail to 628 Virginia Dr., Orlando, FL 32803.

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