A panel of independent advisers from the Centers for Disease Control and Prevention will meet on Thursday to discuss whether some patients may need additional doses of the COVID-19 vaccine.
There is growing concern that patients with weakened immune systems – including those with autoimmune diseases, HIV patients, cancer patients and organ transplant recipients – may be vulnerable to COVID-19 even after full vaccination.
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Such patients may require a second or third dose of the vaccine, depending on which vaccine they have received. (Modern and Pfizer-BioNtech’s mRNA vaccines require two doses, while the Johnson & Johnson vaccine requires only one.)
For example, Israel has begun offering a third dose of the Pfizer vaccine to people with weakened immune systems.
While vaccines still appear to reduce the risk of hospitalization and death in immune-compromised people, “there is clearly a difference between those patients and those with normal immune systems,” says an occupational medicine specialist. , said Dr. Melanie Swift, co-chair of Mayo Clinic’s COVID-19 Vaccine Allocation and Distribution Workgroup.
Céline Gounder, an infectious disease specialist and epidemiologist at New York University at Bellevue Hospital, said such an update to vaccine recommendations would not mean that “vaccines don’t work.”
“That means we’re still figuring out the best dosing regimen,” Gounder said.
As the highly infectious Delta variant spreads across the country, “it makes it all the more important that we have a very strong immune response” from vaccines, Gunder said. The CDC reported Tuesday that the variant accounts for 83 percent of new cases in the US.
It is not unusual for vaccines to require multiple doses. human papillomavirus The vaccine is given in two doses, and a third to people with weakened immune systems. two or three doses of vaccine for prevention brain fever Depending on the type of vaccine also needed. And this Hepatitis B vaccine Up to four shots are given.
independent panel of experts, called Advisory Committee on Immunization Practices, Thursday’s meeting is not expected to suggest changes to vaccine guidance. The panel also discussed additional doses last month, concluding that there was not yet enough evidence that they were needed for the general population.
But increased immunity may be necessary in some groups. a study of Cancer Patient Published in June found that even if such patients responded well to the vaccines, it is not clear how long their protection might last.
other research May found different immune responses among some cancer patients, “particularly patients with blood cancers, what we call hematologic malignancies, who also require highly immunosuppressant drugs,” Gounder said.
Organ transplant recipients may also require additional doses. They must take medicines to suppress their immune systems so that their bodies do not reject the new organs. Those drugs can also reduce the body’s response to vaccines.
A small study of 30 organ transplant recipients published in June suggested the need for a third dose. Even though all participants were fully vaccinated with Moderna or Pfizer-BioNTech vaccines, most had no antibodies to the virus. Others had low levels of antibody response.
A third dose, the researchers said, somewhat enhanced the antibody response, but more studies are needed to determine which patients may benefit the most.
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Whether an additional dose will eventually be needed can be analyzed in two ways. Are fully immunized patients facing breakthrough infections that are making them sick? And do blood samples from those patients indicate lower levels of immunity than patients with normal immune systems?
Looking at the immune response goes beyond measuring antibody levels, Swift said.
“Some of these people will never develop a measurable neutralizing antibody, but does that mean they are not safe?” he said. Antibodies are not the only measure of the strength and strength of the immune system. Other cells, such as T cells and memory B cells, also play a role, but they are not easily measured in laboratory tests.
All three manufacturers of authorized COVID-19 vaccines in the US are investigating the safety and effectiveness of additional doses.
National Institute of Allergy and Infectious Diseases has also launched clinical trial To determine whether a person can be given a third shot of Moderna vaccine after they have already been fully immunized with Pfizer or Johnson & Johnson vaccines.
The results of those tests are expected sometime this summer.
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