Keith Roach, M.D., syndicated columnist

DEAR DR. ROACH: Perhaps you have noticed all the commercials on television advertising every kind of medication you can think of. Occasionally, I will see an ad stating that if you take the medication they are advertising, there is a certain percentage of effectiveness quoted.

For example, one ad said that there was an 85% rate of protection for those who took the medication. My question is, what happens to the unfortunate few who are in the 15%? — D.D.

ANSWER: The answer really depends on the particular condition. Since you mention “protection,” I can think of many ads I see for the shingles vaccine. In this case, the vaccine is effective at preventing the disease entirely.

Medication taken regularly to prevent HIV infection (pre-exposure prophylaxis, or PrEP) is about 99% effective for people who are compliant with treatment. Unfortunately, when the rare person on PrEP does get an infection, they are more likely to acquire a drug-resistant strain, so the preventive treatment was not helpful for them in this case

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