Advisers to the US Centres for Disease Control and Prevention on Thursday will consider evidence suggesting that a booster dose of Covid-19 vaccines could increase protection among people with compromised immune systems.
Data presented ahead of the meeting noted that such people have a reduced antibody response following the recommended primary vaccination series compared with healthy individuals.
"Emerging data suggest that an additional Covid-19 vaccine dose in immunocompromised people enhances antibody response and increases the proportion who respond," slides released ahead of the meeting showed.
The committee is not scheduled to vote on a recommendation for whether to administer additional doses. That could be decided at a later meeting.
In small studies, short-term side effects from a third dose of mRNA vaccines - such as those made by BioNTech/Pfizer Inc or Moderna Inc - were about the same as those experienced with the first two doses, the CDC said in its presentation.
An estimated 2.7 percent of US adults live with weakened immune systems, according to the CDC presentation, based on data from 2013. The group includes people living with HIV/AIDS, cancer and people with organ transplants or autoimmune diseases who take drugs to dampen their immune response.
Those individuals are at increased risk of severe disease and death from Covid-19.
Last week, Israel began administering third doses of the Pfizer/BioNTech vaccine to immunocompromised people, including those who have had heart, lung, kidney or liver transplants and cancer patients receiving chemotherapy.
Some experts believe the CDC is nearing a similar recommendation in the United States.
The CDC has urged people with weakened immune systems to take precautions even if fully vaccinated against Covid-19.
The virus not only poses an extra health risk to these people but because it takes longer for them to clear the virus, scientists believe infections could result in new variants as the pathogen continues to replicate unchecked, which some studies have shown.