Editor's note: Information on the COVID-19 crisis is constantly changing. For the latest numbers and updates, keep checking the CDC's website. For the most up-to-date information from Michigan Medicine, visit the hospital's Coronavirus (COVID-19) webpage.

On May 13th, the Centers for Disease Control and Prevention updated its guidance for people who'd been fully vaccinated against COVID-19. If at least two weeks had passed since your final shot, you were cleared, the CDC stated, to return to normal life.

Yet the CDC only briefly mentioned one group that should remain cautious, even if they're fully vaccinated: those who are immunocompromised.

These are people whose immune systems don't mount a strong — or sometimes any — response to potential invaders, which already leaves them more vulnerable to infection and illness, including COVID-19.

Adding to the problem is that COVID-19 vaccines may not provide as much protection for some who are immunocompromised compared to the general population.

"The limited data that we have creates significant concerns that vaccines against COVID-19 may not be as effective in immunosuppressed patients," says Daniel Kaul, M.D., director of the Transplant Infectious Disease Service at Michigan Medicine.

But the situation is complex. If you are immunocompromised or have a loved one who falls into this category, here's what you need to know.

Jump to sections about:

What causes people to be immunocompromised

Why immunocompromised people should get vaccinated

The timing of vaccination for immunocompromised people

How to measure your response to the vaccine if you're immunocompromised

Why immunocompromised people shouldn't go "back to normal" yet

How immunocompromised people should remain cautious after vaccination

How long immunocompromised people will have to be careful in their daily activities

What people with loved ones who are immunocompromised can do to protect them

What causes people to be immunocompromised?

A lot of different people are lumped under the immunocompromised umbrella. Those with autoimmune or inflammatory conditions, such as rheumatoid arthritis, lupus and inflammatory bowel disease, certainly qualify.

HIV is another culprit of immunosuppression as are stem cell transplants and blood cancers like leukemia and lymphoma.

Yet another group of immunocompromised people are those who take medications that artificially weaken their immune systems. These can be:

• People receiving chemotherapy, immunotherapy or other aggressive treatment for cancer

• Those who have had organ transplants and are taking drugs that keep their bodies from rejecting their new organs

• Anyone with an autoimmune condition who's on medication to try to prevent their immune system from attacking itself

Should immunocompromised people get vaccinated against COVID-19? If so, when?

Yes. Immunocompromised people are at greater risk of contracting the coronavirus and of developing more severe cases of COVID-19, so it's crucial they get vaccinated.

But protecting yourself from the coronavirus if your immune system is suppressed isn't always as simple as getting a jab once or twice in the arm.

For a portion of immunocompromised people, the timing of their vaccination becomes more important as a result of their condition.

For instance, the National Cancer Institute recommends those receiving aggressive chemotherapy wait to get vaccinated until their blood cell counts start to return to normal levels. (Ask your doctor if you're not sure whether your chemo qualifies as "aggressive.")

The NCI also suggests that people who have had a certain type of immunotherapy called CAR T-cell therapy and stem cell transplants delay vaccination until at least three months after their treatment ends.

Many health systems already offer programs that allow those who have had stem cell transplants to repeat their childhood vaccinations since all the immunity they developed to contagious diseases is partially lost when their stem cells are replaced.

Michigan Medicine's re-vaccination initiative generally starts at six months post-transplant, but John Magenau, M.D., the adult clinical BMT director of the Blood and Marrow Transplantation Program at Michigan Medicine, says patients who've discussed the issue with their transplant physician and decided the benefits outweigh the risks of COVID-19 vaccination could get the vaccine as early as three or four months after their stem cell transplants.

Kaul recommends those who have had solid organ — i.e., liver, heart, kidney, lung, pancreas — transplants wait to get the COVID-19 vaccine until one to three months after their operations.

The American College of Rheumatology has created detailed guidelines around vaccination timing for people with autoimmune and inflammatory conditions as well as recommendations for which medications should be paused when patients get the vaccine.

They vary widely depending on the medication and how well the underlying disease is controlled. But Jiha Lee, M.D., a clinical assistant professor of rheumatology and internal medicine at the University of Michigan Medical School, pointed to the guidelines around rituximab, a powerful medication used to treat certain autoimmune conditions and cancers, as some of the most important to note.

She says vaccination should be delayed until at least five months after the last infusion of this potent immunosuppressant and that it should preferably be scheduled four weeks before the patient's next cycle of rituximab.

"We've had instances where patients were not aware of this information and received vaccination without an immune system response," she says.

A New York-based study, too, found that 66% of patients on rituximab did not generate antibodies after receiving the COVID-19 vaccine, and a negative response was more likely if a patient was vaccinated closer to their last dose of the potent immunosuppressant. (Jump to, "So, if I don't produce antibodies in response to the vaccine, do I need to be concerned about whether the vaccine is working for me?" for more information.)

Finally, there's one big asterisk to vaccination for immunocompromised people: Outside of those with HIV, this population wasn't studied in the large clinical trials Pfizer-BioNTech, Johnson & Johnson and Moderna conducted to see whether their vaccines worked. So how well the COVID-19 vaccines protect immunocompromised people remains unclear — although initial studies raise concerns that protection might not be as strong.

If we're not sure how well the COVID vaccines work in immunocompromised people, why should these people get vaccinated?

No. 1: Any protection is better than none.

"While it's highly likely that vaccines in immunocompromised people won't be as effective as they are in immunocompetent people, because that's true in most vaccines, we hope they'll provide a degree of protection, even if it's not complete," Kaul says.

No. 2: In general, immunocompromised people haven't experienced severe health issues as a result of the COVID-19 vaccines.

No. 3: Immunocompromised people are not all the same in the way their immune systems react to threats.

If you're on a short course of traditional chemo, for instance, your immune system tends to be weaker — but only temporarily. (This is not the case if you have an underlying health condition that permanently depletes your immune system.)

Once you're done with chemo, your immune system will likely recover, so you probably don't need to be concerned about mounting less of a response to the vaccine, as long as you time your COVID-19 vaccination around when you're not actively receiving treatment.

On the other end of the spectrum are people who have had organ transplants. They need to be on immunosuppressing medication for life; otherwise, their bodies could reject their new organs.

And emerging data shows they may be more susceptible to COVID-19 after getting vaccinated than the general population.

In a recent study, researchers from Johns Hopkins University analyzed more than 600 people who'd undergone liver, heart, kidney and other organ transplants and had received two doses of either the Pfizer-BioNTech or Moderna vaccines.

Fifty-four percent had an antibody response after at least one dose of the vaccine, yet the levels of their antibodies were consistently lower than what's seen in those with healthy immune systems.

In comparison, a study of more than 100 people with autoimmune and musculoskeletal conditions — including lupus, Sjogren's syndrome, inflammatory arthritis and mixed connective tissue diseases — found that 74% had generated antibodies after just one dose of the COVID-19 vaccine.

So, if I don't produce antibodies in response to the vaccine, do I need to be concerned about whether the vaccine is working for me?

Not necessarily.

A quick antibody 101: Antibodies are proteins that attach to what the immune system deems enemies — typically organisms like viruses or bacteria. When the antibodies bind to the "enemies," this may prevent disease from developing and serves as a signal to the rest of the immune system that these are uninvited guests who need to be dealt with pronto.

As a result, researchers have used the antibody response as a measure of immunity against select viruses and bacteria, including the influenza viruses and the bacteria that causes pneumococcal diseases, of which pneumonia is the most common.

And past studies have shown that certain groups of immunocompromised people don't have the same kind of antibody response as the general population to the flu and pneumococcal vaccines, partly because of the medications they take.

SEE ALSO: The Forecast for COVID Vaccines for Kids

But antibodies are just one part of a very complex system. The immune system includes lots of other components that are essential in defeating everything from the common cold to COVID-19. And those other elements may be reporting for duty in large numbers after you get the vaccine, but an antibody test won't tell you that.

Plus, just because the antibody response served as a decent metric for other vaccines does not necessarily make it the best or only way to assess your immunity to COVID-19.

"Every virus is different, and every vaccine is different," Kaul says. "Different vaccines stimulate different parts of the immune system, so we can't necessarily say that you're protected if you generate antibodies or not."

"In time, I think we'll get more information," he says. "The clinical trials that were done on vaccines may tell us what parameters we can measure in the blood or in cells that correlate with immunity. But right now, we don't have that information for anyone, let alone immunocompromised people."

Although researchers are studying antibody tests in clinical trials, Michigan Medicine does not recommend getting them after vaccination. Right now, the FDA has recommended against antibody testing post-vaccination since, as Kaul says, "we don't really know what to do with the results."

"What we know with 100% certainty is the much more important thing that in immunocompetent people, the vaccine works," Kaul says. "One of the most important things to keep an eye on going forward is how frequently will fully vaccinated immunocompromised people develop severe COVID-19? If this is happening at a high rate, it would suggest that the current vaccination strategy for immunocompromised people is not getting the job done."

So, why can't immunocompromised people just go back to normal, like everyone else?

First off, there are plenty of locations where no one should go "back to normal" yet. (Check out "Confused About the Latest Mask Rules? Read This" for more details.)

Second: Unfortunately, we're still gathering data about the likelihood of an immunocompromised person developing a severe case of COVID-19 or dying from the disease after getting the vaccine. Protection will probably vary widely among people whose immune systems are suppressed in different ways.

But, if the vaccine provides a lower level of immunity for at least some of these folks, and they're more vulnerable to contracting the coronavirus already, it's essential that they're careful about where they go and with whom they spend their time.

So, what should I do if I'm immunocompromised and have been vaccinated?

"I advise my patients to follow the guidelines as if they're not vaccinated, to exercise maximal caution," Lee says. "I tell them you're better protected than you were before, but that doesn't mean you have the same degree of protection as somebody who doesn't have your condition or is not on your medication."

"These are difficult decisions that each person has to make on their own," Kaul says, "But my general advice would be to take sensible precautions if the coronavirus is still circulating at high levels in your community."

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That means avoiding crowds as well as socially distancing and wearing a mask, preferably an N95 if you can find one, in all indoor settings where you have to interact with someone who may not be vaccinated. Think: grocery stores and gyms.

Small outdoor gatherings are safer than those indoors with people who are vaccinated, which, in turn, are safer than indoor functions with people who aren't vaccinated. Going mask-free is OK in the first two situations, Kaul says. But talk to your doctor about your risk level based on your specific medical history and medications. And, if you feel safer with a mask, wear one.

In addition, try to be thoughtful about your travel plans.

A vacation that involves driving to a remote beach where you can avoid high-risk contacts is relatively safe whereas more transmission has occurred during longer international flights, so you should steer clear of those if possible.

Especially since you 1) may have difficulty traveling back to the United States depending on the visitor restrictions in that specific country and 2) if you have an underlying health condition or medical needs, the health systems in many countries — including Brazil, Mexico and parts of Asia — remain strained, and it will likely be difficult to find medical care in an emergency.

Finally, take extra caution if you're immunocompromised and you have children who aren't yet vaccinated or aren't eligible to be vaccinated. Try to minimize your kids' exposures if they're under 12 especially.

"It's another tough situation," Kaul says. "You can't keep kids away from each other forever."

If I'm immunocompromised, how long do I have to remain this careful?

More research is being done on this topic, so there will ideally be more information about which types of immunocompromised people are most vulnerable to COVID-19 after getting the vaccines and how best to measure immunity as time goes on.

Magenau is optimistic about the outlook for those who have had stem cell transplants, given their lack of side effects and even a few immune system responses he's seen to COVID-19 vaccines in some patients.

"In lieu of good data, we're making an educated guess while informing patients about their risks and benefits," he says. "But I'm encouraged. We're not letting this slow down our practice. We are also encouraging caregivers to strongly consider receiving the vaccine."

Michigan Medicine plans to record vaccine responses in people who have had stem cell transplants as part of a research collaboration with the Blood and Marrow Transplant Clinical Trials Network, and the rheumatology division has created a registry to document any side effects and flares that arise in those with rheumatic diseases after vaccination.

Conversations are also being had about ways to make the vaccines more effective for immunocompromised people.

In the same way the Johnson & Johnson vaccine is often recommended as a booster shot for those who have some natural protection against COVID-19 because they've already been infected with it, immunocompromised people may eventually get additional doses of the vaccine — or doses of a different COVID-19 vaccine than they were originally inoculated with — to boost their immune system's response.

SEE ALSO: Should Pregnant and Breastfeeding Patients Get the COVID-19 Vaccine?

This tactic has worked well in the past for immunocompromised people who don't respond to the flu vaccine.

"We don't have hard data yet," Lee says, "but I think this is going to be on the horizon."

Ultimately, certain classes of immunocompromised people may be encouraged to limit their exposure to riskier people and settings until a large portion of society is vaccinated.

"It's really going to depend on herd immunity," Lee says. "People with rheumatic illnesses can take all the precautions, however, if the people they're surrounded by are unvaccinated or the COVID-19 infection rates are continuously rising, it becomes harder because they have diseases that won't go away, and a lot of them are committed to these high-risk medications for life. So I think their ability to return to normalcy will depend largely on how the community continues with vaccination efforts."

"It's a difficult situation," Kaul says. "There isn't necessarily an endpoint on it. I don't think we're going to be able to entirely eradicate the spread of COVID-19, so in a way, people who are immunocompromised are most dependent on others getting vaccinated because that can decrease the spread."

What should I do if a person I love is immunocompromised?

You can get vaccinated.

Although masks do provide some protection for the wearer, they're largely about protecting others.

And, because of the uncertainty around whether the COVID-19 vaccine protects immunocompromised people to the same degree as the general population, this vulnerable group must rely on those around them to reduce their risk of getting sick.

"When individuals are making decisions about being vaccinated," Kaul says, "one thing they might want to consider is that they're protecting their neighbors, the people they go to church with, the people they socialize with who may be immunocompromised and may not be able to respond as well to the vaccine."

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