Research is ongoing, but the CDC says those who are immunocompromised may still need to take extra precautions, even after vaccination

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Ever since the pandemic began, public health officials have warned that people who are immunocompromised need to be especially cautious to try to avoid catching COVID-19. Now that the COVID-19 vaccine is available to all Americans over the age of 12, there are still warnings for immunocompromised people to be careful-even if they're fully vaccinated.

In fact, the Centers for Disease Control and Prevention (CDC) specifically says this online: "If you have a condition or are taking medications that weaken your immune system, you may NOT be fully protected even if you are fully vaccinated. Talk to your healthcare provider. Even after vaccination, you may need to continue taking all precautions."

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Credit: AdobeStock / Photo Illustration by Jo Imperio for Health

If you're not immunocompromised or if you don't have a close friend or family member with a weakened immune system, you probably haven't given this much thought. But if you or someone you know does fall into the immunocompromised population-of which there are an estimated 10 million people in the US alone, according to the Johns Hopkins Bloomberg School of Public Health-it's understandable to have questions. Here's what you need to know.

What does it mean to be immunocompromised, again?

People who are immunocompromised have a weakened immune system, according to the National Cancer Institute (NCI). That means they aren't able to fight infections and other diseases as well as others who aren't immunocompromised.

There are several health conditions and diseases that can cause a person to be immunocompromised, including AIDS, cancer, diabetes, malnutrition, and certain genetic disorders, NCI says, and some medications and treatments like anticancer drugs, radiation therapy, stem cell, or organ transplant can also make a person immunosuppressed.

Why might immunocompromised people not be fully protected by the COVID-19 vaccine?

In general, people who are immunocompromised may not respond to vaccines as well as those who aren't immunocompromised, John Sellick, Jr., DO, an infectious disease expert and professor of medicine at the University at Buffalo/SUNY, tells Health. "We knew this was going to be a problem with the COVID-19 vaccine all along," he says.

Research has also found that SARS-CoV-2, the virus that causes COVID-19, can cause more severe illness in people who are immunocompromised and even survive longer in their bodies because their immune systems generate a weaker response.

But there isn't a ton of research about how much protection the COVID-19 vaccine will provide to people who are immunocompromised. "We are still beginning to learn about the immune response generated by patients who are immunocompromised after COVID vaccination," Prathit Kulkarni, MD, assistant professor of medicine in infectious diseases at Baylor College of Medicine, tells Health. "In some instances, it is possible that patients who are immunocompromised might not generate as robust an immune response." As a result, he says, "they may remain susceptible" to contracting COVID-19, even if they've been fully vaccinated.

A recent study published in JAMA found as much. That study analyzed data from people who received organ transplants and an mRNA COVID-19 vaccine-the two currently available in the US of that kind are made by Pfizer and Moderna-and found that only 15% had antibodies to the virus after the first vaccine. After the second dose, 54% had the antibodies.

But Dr. Sellick says it's slightly tricky to apply those findings to all people who are immunocompromised, given that they only studied one segment of the immunocompromised population-that is, people who received organ transplants. "The problem is defining what 'immunocompromised' is," he says. "It's not just transplant patients."

"The state of being immunocompromised is quite variable," Dr. Kulkarni explains. "Some forms of immunocompromise, such as chemotherapy for leukemia or medications that need to be taken after organ transplantation, can be quite significant. There is a range of what constitutes the immunocompromised state, and different situations might pose a different risk."

The data also just looked at antibodies, which are only one aspect of immunity, Dr. Sellick points out. And, he says, doctors "don't really understand" at this moment how other immune factors like T cells may impact a person's immunity to the virus. Dr. Kulkarni agrees. "The effects of vaccination on response from T cells, another part of the immune system, are also not fully known at this point," he says.

There's also this to consider: Immunocompromised people weren't included in the original clinical trials for the COVID-19 vaccines. "For practical reasons during the middle of the pandemic, it was needed to proceed quickly to determine the safety and efficacy of the COVID vaccines," Dr. Kulkarni says. "This did create a gap in our understanding of the immune response to vaccine in this particular group of patients." But, he adds, "research is actively ongoing in this area to help us understand the situation further for these patients."

So what should you do about the COVID-19 vaccine if you're immunocompromised?

Experts say it's still important to get the vaccinated, and the CDC also recommends this. "Currently, immunocompromised patients are recommended to receive any of the standard COVID vaccines," Dr. Kulkarni says.

The vaccine is especially important for people who are immunocompromised because they "could be at higher risk for a worse outcome from COVID-19 depending upon their particular type of immunocompromised state," Dr. Kulkarni says. And that, he says, is why mask use and physical distancing are still important if you have a weakened immune system-even if you are fully vaccinated.

It's unclear at this point what will be done to make the COVID-19 vaccines more effective in people who are immunocompromised. "Maybe we'll do what we do with dialysis patients and give booster doses," Dr. Sellick says. "We also have high-dose vaccines for influenza that give you more antibodies-a higher dose could be a possibility for COVID-19."

In fact, a small study in the Annals of Internal Medicine suggests a booster may be helpful for at least some patients. The study involved 30 organ transplant recipients, all of whom either had no or very low levels of antibodies against the virus after their initial two doses of an mRNA vaccine (Pfizer or Moderna).

Two weeks after receiving a third dose of vaccine-either Pfizer, Moderna, or Johnson & Johnson-patients' antibody levels were checked again. Six patients who started off with low antibody levels after the first two doses wound up with higher antibody levels after the booster. Among the remaining 24 patients with no antibodies at the start, six has higher levels and two had at least low levels after a third dose.

The authors of the study say the findings point to the need for clinical trials to assess whether organ transplant patients should receive a booster dose.

Ultimately, Dr. Sellick says, there are still questions about the effectiveness of the vaccine in people who are immunocompromised. "We're just not there yet," he says.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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