It's why vaccinations are still recommended for people with immune systems weakened by disease or certain medications. It's also important that your family, friends and caregivers get vaccinated, which will make it far less likely that they pass on the virus.

About 3% of US adults have weakened immune systems. Among them are people with HIV or AIDS, transplant recipients, some cancer patients and people with autoimmune disorders such as rheumatoid arthritis, inflammatory bowel disease and lupus.

COVID-19 shots weren't studied in large numbers of people with weak immune systems. But limited data and experience with flu and pneumonia vaccines suggest they won't work as well as they do in others. That means people with weakened immune systems should keep taking precautions like wearing masks and avoiding large crowds.

“It's prudent to use all the precautions you were using before you were vaccinated,” said Dr. Ajit Limaye, a transplant expert at University of Washington Medicine in Seattle.

Although most cancer patients should get vaccinated as soon as they can, people getting stem cell transplant or CAR T-cell therapy should wait at least three months after treatment to get vaccinated, according to guidance? from the National Comprehensive Cancer Network. That delay will make sure the vaccines work as well as they can.

For transplant recipients, researchers are looking at whether an extra dose? might make the vaccines more effective.

French guidelines recommend a third COVID-19 dose? for the immunocompromised, including organ recipients. Israel recently began giving an extra dose of the Pfizer vaccine to transplant patients and others with weak immune systems. Some U.S. transplant recipients seek out a third dose on their own in hopes of more protection even though the federal government hasn't authorized extra vaccinations.