DEAR DR. ROACH: Recently, in the middle of all the news about the newly circulating delta COVID-19 variant, a friend of mine flew to Mexico with her husband and teenage daughter for a five-day resort vacation. After she returned, she went to an outdoor concert with a group of friends, and the following day went to an indoor event with several good friends. The day after that, she began developing flulike symptoms and went to the doctor, who told her she had COVID. At her insistence, all the people she had been in close contact with, as well as her husband and daughter, were tested for COVID. My friend drinks alcohol (wine and margaritas) recreationally nearly every day. Could that have had an effect on her immune system? — J.T.M.

ANSWER: I’m afraid your friend has made some unwise choices. The delta variant is much more infectious than the previous variants of SARS-CoV-2, the virus that causes COVID-19. Indoor events are much more likely to allow spread of the virus, so I recommend not attending large indoor events, and to use masks when you are indoors with anyone besides your own family. This is true if you are in an area of substantial or high transmission, which nearly all of North America is in at the time of this writing.

Alcohol absolutely has multiple effects on the immune system. Alcohol has deleterious effects on the gastrointestinal system, on the lungs and the rest of the respiratory system, and on the various cells of the immune system directly. Because of these effects, alcohol makes a person more susceptible to, and more likely to get severe disease from, COVID-19.

In general, the greater the dose of alcohol, the worse the effect on the body’s systems. A half-glass of wine a day has minimal ill effects. However, it sounds like your friend may be drinking more than that.

It is not at all necessary to be a drinker to get COVID-19 disease, but excess alcohol consumption absolutely makes the risk of acquiring COVID-19, and of developing complications, significantly worse.

DEAR DR, ROACH: I am 73-year-old male and a frequent platelet donor — 18 to 22 times a year for past six years. I used to donate blood (I’m A positive) four to six times a year. I did both before regularly donating platelets due to what I believed there was a greater need for platelets. Is it safe to give platelets so often? — B.M.C.

ANSWER: Thank you for donating. There are national shortages in both blood and platelets, but platelets are critically low in many areas, and must be used within five days of donation, so a steady supply of donations is essential.

A single donation of platelets is about 3 to 4 billion platelets, which are needed for blood clotting. One donation will not cause the donor’s platelets to go too low, but there is a risk of too-low platelets with excess donations.

For this reason, the U.S. Food and Drug Administration has placed a limit of 24 donations per year. At this level, low platelets in the donors were rarely seen. You are donating at a safe level.

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— 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 ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.