Why Are Some People More Susceptible to Infection?

Heidi Zapata, MD, PhD, assistant professor of medicine (infectious diseases) at Yale School of Medicine, is fascinated by microbes—bacteria, viruses, fungi, and parasites too small to be seen with the naked eye. “That’s what led me to infectious diseases,” she said.

Zapata’s interest grew when she found that, among her patients, the same microbe could produce mild disease in one person and an overwhelming sepsis in another.

“I truly want to understand the individual immune response,” she said. “Why are some people completely asymptomatic while others die from the same infection?”

Zapata’s research focuses on understanding how aging, HIV infection, and comorbid conditions affect the innate immune response in humans. Currently, she is investigating how the adipose tissue immune microenvironment contributes to the body’s overall immune response.

In a Q&A, Zapata discusses the factors that influence a person’s immune response, ways to increase our immunity, and her hopes for tailored medicine.

Everyone is different. For example, some older adults are running marathons, while others are sick with numerous comorbid conditions. There is an incredible amount of human variation when it comes to responding to infections. We all have an individual immune response, and we need more research to understand why that is.

Evidence shows that men and women respond differently to infection because different parts of their immune systems are enhanced. Men have a more robust innate immune response, while women have more of what we call an adaptive and memory immune response. So even biological sex plays a role.

Age is also a factor. During the COVID-19 pandemic, older adults had more severe disease than young people. Another example is the West Nile virus, which is going around right now. Some people don’t even realize they have the virus, while others, especially older adults, will develop severe symptoms such as meningitis and encephalitis.

Comorbid conditions, like diabetes, and an individual’s level of immunocompromise also play a role. Ongoing cancer, a transplant, or drugs that change your immune system all contribute to how we respond to a microbe.

There are some simple things we can do. First of all, it’s important to be on top of your medical conditions. If you have diabetes or high blood pressure, make sure they’re well-controlled.

Consider getting vaccinated—there’s a new COVID booster, flu shot, and RSV vaccine—especially if you are an older adult.

Eat less greasy, fatty foods, which can cause inflammation. A lot of investigation has been done on the Mediterranean diet and its anti-inflammatory effects. Eating healthy makes a difference.

Ultimately, I hope we can tailor interventions to individuals. A vaccine for a healthy young adult should be different from one given to an older person who’s immunocompromised.

It’s important that this line of research continues because COVID-19 is probably not our last pandemic.

Yale School of Medicine’s Department of Internal Medicine Section of Infectious Diseases engages in comprehensive and innovative patient care, research, and educational activities for a broad range of infectious diseases. Learn more at Infectious Diseases.