DEAR DR. ROACH: You recently posted a couple of articles about the respiratory syncytial virus (RSV) vaccine and the benefits versus the risks. I know the risks are based on data. But I wonder how many people have severe reactions to the vaccine, and it doesn’t get reported because they don’t end up going to the hospital or the doctor.

I recently received the latest COVID and RSV vaccines, and four days later, I started experiencing extreme nausea and vomiting for two days, along with muscle aches, tingling, and hot and cold flashes. I was miserable and couldn’t sleep. This happened over the weekend. If it had lasted until Monday, I would have gone to urgent care. But by Monday morning, I was feeling better, so it was never reported.

I’m a 67-year-old female in relatively good health. But I feel like someone older experiencing what I experienced over the weekend could be very dangerous. I tried to drink as much water as I could, but it made me nauseous, as did any food. So, I ended up being pretty dehydrated. My point is that my fairly severe reaction was not reported, and I wonder how underreported these data really are. — T.B.

ANSWER: I am sure you are right that many adverse vaccine events are not reported. Most patients don’t report expected side effects from vaccines, and even when they do, a minority of providers will make a report to VAERS, the Vaccine Adverse Event Reporting System at the Centers for Disease Control.

However, providers are mandated by law to report certain serious adverse events from vaccines (those that are listed in the table of reportable events, which is vaccine-specific) or any adverse event that is listed by the manufacturer, which would prevent the person from getting any more doses of this vaccine.

I report unexpected side effects to VAERS, although most of my colleagues do not always do so. Many people do not know that they can also self-report to the VAERS system by going to VAERS.HHS.gov/reportevent.html.

The data on adverse events that I generally use for my column do not come from self-reports or physician reports; they come from the original studies on the vaccines, where all adverse events are carefully reported.

For RSV in particular, this means a study published in 2022 from Belgium, which showed that 72% of vaccine recipients (and 28% of the recipients who received a placebo, plain salt water) had at least one adverse reaction. The most common symptom was pain at the injection site (61%), but headache, fatigue and muscle aches were also fairly common.

Nausea and vomiting were not reported as side effects in the paper for RSV. However, nausea and vomiting were reported in 9% of Moderna COVID-19 vaccine recipients, compared to 8% in the placebo group. Taking the two vaccines at the same time makes side effects more likely and also makes it impossible to tell for certain which vaccine caused the side effect.

You are correct that there is underreporting of adverse effects from vaccines; however, in the vast majority of cases, the side effects from the vaccine are relatively mild and much less dangerous than getting the actual disease.

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. (c) 2025 North America Syndicate Inc. All Rights Reserved