While they've been around long before COVID-19, comorbidities are increasingly being discussed as vaccination rollout continues across the nation. Find out the meaning of comorbidity — plus how it affects coronavirus, according to experts.

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By this point in the coronavirus pandemic, you've likely become familiar with a veritable dictionary worth of new words and phrases: social distancing, ventilator, pulse oximeter, spike proteins, among many others. The latest term to join the dialogue? Comorbidity.

And while comorbidity is nothing novel in the medical world, the term is increasingly being discussed as coronavirus vaccination continues to roll out. That's due largely in part to the fact that some areas have moved beyond vaccinating only frontline essential workers and those 75 and older to now include people with certain comorbidities or underlying health conditions. For example, Queer Eye's Jonathan Van Ness recently took to Instagram to urge people to "check the lists and see if you can get in line" after discovering that his HIV-positive status made him eligible for vaccination in New York.

So, HIV is a comorbidity...but what does that mean exactly? And what other health issues are also considered comorbidities? Ahead, experts help explain everything you need to know about comorbidity in general and comorbidity as it relates specifically to COVID.

What is comorbidity?  

Essentially, comorbidity means that someone has more than one disease or chronic condition at the same time, according to the Centers for Disease Control and Prevention (CDC). Comorbidities are usually used to describe "other medical conditions that a person may have that can worsen any other condition they may [also] develop," explains infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. So, having a particular condition could put you at a higher risk for a worsened outcome if you happen to develop another illness, such as COVID-19.

While comorbidity has come up a lot in the context of COVID-19, it exists for other health conditions, too. "In general, if you have some pre-existing illness such as cancer, chronic kidney disease, or severe obesity, it puts you at risk for greater illness for a number of diseases, including infectious diseases," says Martin Blaser, M.D., director of the Center for Advanced Biotechnology and Medicine at the Rutgers Robert Wood Johnson Medical School. Meaning: A comorbidity is only when you have two or more conditions at the same time, so if you have, say, type 2 diabetes, you'd have comorbidity if you actually contracted COVID-19.

But "if you're perfectly healthy — you're in good shape and [have] no diseases — then you have no known comorbidities," says Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York.  

How does comorbidity affect COVID-19?

It's possible to have an underlying health condition, contract SARS-CoV-2 (the virus that causes COVID-19), and be just fine; but your underlying health condition may put you at higher risk of having a severe form of the disease, says Dr. Adalja. (FYI — the CDC defines "severe illness from COVID-19" as hospitalization, admission to the ICU, intubation or mechanical ventilation, or death.)

"Comorbidities often worsen many viral infections because they decrease the physiological reserve a person may have," he explains. For example, a person with chronic lung disease (i.e. COPD) might already have weakened lungs and respiratory ability. "Comorbidities can often cause preexisting damage at a site where a virus may infect," he adds.

This can increase the chances that COVID-19 will do more damage to those areas (i.e. the lungs, heart, brain) than it would in someone who is otherwise healthy. People with some comorbidities also may simply have an immune system that, in Dr. Russo's words, "is not up to snuff" because of their underlying health condition, making them more likely to get COVID-19 in the first place, he says. (Related: Here's Everything You Need to Know About Coronavirus and Immune Deficiencies)

But not all pre-existing conditions are equal. So, while having acne, for example, is not thought to cause serious harm to you if get sick, other underlying medical Issues — i.e. diabetes, heart disease — have been shown to raise your risk of severe COVID-19 symptoms. In fact, a June 2020 study analyzed data from peer-reviewed articles published from January to April 20, 2020, and found that people with underlying health conditions and the potential for comorbidity have a higher risk of developing severe illness and even dying from COVID-19. "Patients with comorbidities should take all necessary precautions to avoid getting infected with SARS CoV-2, as they usually have the worst prognosis," wrote the researchers, who also found that patients with the following underlying issues were at the highest risk of severe disease:

  • Hypertension
  • Obesity
  • Chronic lung disease
  • Diabetes
  • Heart disease

Other comorbidities for severe COVID-19 include cancer, Down syndrome, and pregnancy, according to the CDC, which has a list of comorbid conditions in coronavirus patients. The list is broken down into two sections: conditions that raise a person's risk for severe illness from COVID-19 (such as those already mentioned) and those that might increase your risk of severe disease from COVID-19 (i.e. moderate-to-severe asthma, cystic fibrosis, dementia, HIV).

That said, it's important to remember that the coronavirus is still a novel virus, so there's limited data and information on the full extent of how underlying conditions affect COVID-19 severity. As such, the CDC's list only "includes conditions with sufficient evidence to draw conclusions." (BTW, should you be double-masking to protect against coronavirus?)

What does comorbidity impact the COVID-19 vaccine?

The CDC currently recommends people with comorbidities be included in phase 1C of vaccination — specifically, those that are between the ages of 16 and 64 with underlying health conditions that increase their risk of severe disease from COVID-19. That puts them in line behind health care personnel, residents of long-term care facilities, frontline essential workers, and people aged 75 and older. (Related: 10 Black Essential Workers Share How They're Practicing Self-Care During the Pandemic)

However, every state has created different guidelines for its own vaccine roll-out and, even then, "different states will generate different lists," as to what existing conditions they consider to be of concern, says Dr. Russo.

"Comorbidities are a major factor determining who develops severe COVID-19, who requires hospitalization, and who dies," says Dr. Adalja. "This is why the vaccine is heavily targeted toward those individuals because it will remove the possibility of COVID being a serious illness for them, as well as decrease their ability to spread the disease." (Related: Everything You Need to Know About Johnson & Johnson’s COVID-19 Vaccine)

If you have an underlying health condition and you're not sure if it impacts your vaccine eligibility, talk to your doctor, who should be able to offer guidance.

The information in this story is accurate as of press time. As updates about coronavirus COVID-19 continue to evolve, it’s possible that some information and recommendations in this story have changed since initial publication. We encourage you to check in regularly with resources such as the CDC, the WHO, and your local public health department for the most up-to-date data and recommendations.