Dr. Roach: Is strong reaction to COVID vaccine due to recent illness?

Keith Roach
To Your Health

Dear Dr. Roach: My neighbor was very ill with COVID-19 about three months ago. He has now mostly recovered. He had his first vaccine shot recently and had a severe reaction – so severe that when he contacted his doctor he was sent to urgent care.

I have a theory, but I don’t want to mention it to him unless you think it sounds reasonable. Because he had COVID-19, he acquired antibodies. Having the vaccine then caused in his body a reaction similar to the more severe reactions some people have to the second shot. I suspect that if he gets the second vaccine, his reaction will be even stronger.

Dr. Keith Roach

Must he get the second shot? Or might he have enough protection with the combination of the antibodies from having the virus and then the first vaccine? I think the stress of a severe reaction to a second shot might harm his overall health and might not be necessary.


Dear K.F.: Your theory is reasonable, and is quite plausibly the major reason that people who have had COVID-19 tend to have more side effects from the vaccine. You are also right that the second shot tends to present a greater reaction than the first, in any person, with or without a history of COVID-19, although that is not universal.

I do not recommend skipping the second shot. The studies we have, which show high effectiveness of the vaccines, were done on people who received both doses of the vaccine. While there certainly is some benefit from a single dose of vaccine, the second dose does seem to be critical.

Less than one person in 10,000 gets a serious reaction to the vaccine. A sore arm or a day (or even a few days) of fever and feeling bad are worth it to be as sure as possible to prevent an infection that has claimed the lives of millions of people. Two doses are also necessary to be considered “fully vaccinated,” which, according to the new Centers for Disease Control and Prevention guidelines, means far fewer restrictions.

Dear Dr. Roach: If your hair and fingernails grow really quickly, are you basically a healthy person?


Dear V.V.M.: This is an urban legend. Every person has a speed at which their nails will grow that is largely genetically determined, and a person in good health will grow nails at that speed.

Certain medical conditions, such as malnutrition and thyroid disease, can slow down nail growth. Nail growth is fastest at about age 10, then slows down a bit over the lifetime. Pregnancy may speed up nail growth temporarily. A supplement, biotin, which is a B-type vitamin, does increase nail strength and growth rate in people with brittle nails, but my clinical experience is that its effects vary quite a bit person to person. This is probably because most people get enough biotin in the diet, so a supplement doesn’t really add much. Incidentally, biotin makes the thyroid laboratory tests appear abnormal, but does not actually affect thyroid levels.

While poor health can slow nail growth, fast nail growth doesn’t necessarily mean good health.

Readers may email questions to ToYourGoodHealth@med.cornell.edu.