Does body size affect how well a COVID vaccine works? Experts weigh in
If someone has a headache, they may take an ibuprofen pill. If they have a really bad headache, that person may take more than one.
In other words, they’re increasing their dosage to guarantee relief from their pain. And oftentimes, older, heavier or taller people may need more of the medicine to benefit from its therapeutic effects.
But does the same thinking apply to the COVID-19 vaccines? Not quite, experts say, because medications and vaccines have different goals that work in different ways.
“Vaccines work differently because it’s not about having a certain level of it in your blood, it’s about stimulating the immune system, and most people’s immune system’s will react to a very small amount of whatever it is that they’re being exposed to,” Dr. Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security, told McClatchy News.
“So, it’s not a dose-response relationship. It’s about finding the perfect dose for the immune system to get the right amount of stimulation, and for most vaccines, it’s pretty much ‘one size fits all,’” Adalja added.
Just think about how tiny viruses and bacteria are. The coronavirus is 60 to 140 nanometers across. For reference, a sheet of paper is about 100,000 nanometers thick.
All it takes is a microscopic amount of virus to make someone sick. “That type of principle really applies to vaccines,” too, Adalja said.
“Because immune systems have evolved to respond to such minute quantities of something they deem foreign, for most vaccines it’s the same dose no matter what your size is,” he said.
This also means a person’s size doesn’t affect how quickly they are able to gain immunity from a COVID-19 vaccine, Adalja added.
Developers of the Pfizer-BioNTech vaccine — the first coronavirus shot to be given emergency use authorization — studied how body mass index (BMI), or the measure of body fat based on height and weight, may affect their vaccine’s ability to offer protection against the virus.
The scientists did not find any differences in efficacy among people who are underweight, overweight, obese or in the normal weight range with a single dose, according to Dr. Susanne Doblecki-Lewis, an associate professor of infectious diseases at the University of Miami Miller School of Medicine.
“In other words, the volume of distribution of the drug which is injected into a single muscle and then starts a reaction is independent of the size of the individual and the subsequent immune response,” Doblecki-Lewis, who was the principal investigator of the Moderna COVID-19 vaccine trial at UM, told McClatchy News in an email.
“This is similar to many other medications that do not rely on the distribution within fat or other parts of the body,” she added.
There are some exceptions when it comes to vaccines, though. For example, adults are given higher doses of the Hepatitis B vaccine than children, whereas kids are given higher doses of the Tdap (Tetanus, Diphtheria, Pertussis) shot than adults.
It’s possible children may receive different doses of a COVID-19 vaccine than adults, but scientists will only know the answer after clinical trials determine how much is safe and effective for them.
Researchers with Pfizer-BioNTech and Moderna are testing their coronavirus shots in children as young as 12. No vaccines have been tested in kids younger than that.
Nearly 9 million people in the U.S. have received their first dose of a COVID-19 vaccine as of Monday, according to a Centers for Disease Control and Prevention tracker.
This story was originally published January 12, 2021 at 12:22 PM with the headline "Does body size affect how well a COVID vaccine works? Experts weigh in."
