Talk to Patients About: Why Do Some Vaccinated People Still Get Sick?
By Sean Price Texas Medicine February 2020

 (Click to watch a video of TMA physician leader David L. Lakey, MD, explain how some vaccinated people can still get sick.)


Every so often, physicians encounter a patient who still gets sick despite getting vaccinated against that disease. Patients naturally ask, how could this happen?

There are various reasons, says Alan Howell, MD, an infectious disease specialist in Temple.

For one, “We all get older, and the farther you get away from some vaccinations the immunity is going to wane,” he said. In other rare cases, immunity fails to take hold even in young, recently vaccinated people.

The problem is that no vaccine is 100% effective, according to the U.S. Centers for Disease Control and Prevention (CDC). Depending on the vaccine, 1% to 5% of vaccinated children fail to develop long-term immunity to diseases after vaccination. 

Waning immunity can make those percentages rise. So can failure to take the vaccine properly. Many vaccines require multiple doses, and not everyone gets all the required doses, CDC says.

Struggles with the annual influenza vaccine also feed incorrect perceptions about vaccines’ effectiveness, Dr. Howell adds. Vaccine makers must predict a few months ahead of time which flu strains will be most prevalent, and if they choose incorrectly the shot is less helpful at stopping flu.

The good news is that vaccine makers are creating more effective vaccines, Dr. Howell says. The newest shingles vaccine is a good example. Even people who had been previously immunized with the old vaccine, Zostavax, are now encouraged to get revaccinated with the new vaccine, Shingrix, because it provides greater, longer-lasting protection.

“The science behind vaccinations and what they do to help stimulate the immune system continues to improve,” Dr. Howell said.


Tex Med. 2020;116(2):45
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Last Updated On

February 24, 2020

Originally Published On

January 24, 2020

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Sean Price


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Sean Price is a reporter for Texas Medicine and Texas Medicine Today. He grew up in Fort Worth and graduated from the University of Texas at Austin. He's worked as an award-winning writer and editor for a variety of national magazine, book, and website publishers in New York and Washington. He's also helped produce Texas-based marketing campaigns designed to promote public health. Sean lives in Austin and enjoys hiking, photography, and spending time with his wife and two sons.

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