New York, Aug 31 : Covid-19 vaccination elicited antibody responses in nearly nine out of 10 people with weakened immune systems, although their responses were only about one-third as strong as those mounted by healthy people, according to a study. Researchers at Washington University School of Medicine in St. Louis, US, analysed a group comprising 133 patients each taking at least one immune-suppressing medication for illnesses such as inflammatory bowel disease, rheumatoid arthritis, spondyloarthritis, lupus and multiple sclerosis, who were compared with 53 healthy people. The participants provided blood samples within two weeks before receiving the first dose of the Pfizer or Moderna vaccine and within three weeks after receiving the second dose. The findings, published in the journal Annals of Internal Medicine, showed that all healthy participants and 88.7 per cent of the immunosuppressed participants produced antibodies against the virus that causes Covid-19. However, people treated for autoimmune conditions produce weaker responses than healthy people Since a minimum level of antibodies needed for protection hasn't been established, it has been difficult to say whether the levels achieved by people on immune suppressing drugs are high enough to protect them from severe Covid-19, the researchers said, advocating a need for booster doses in such groups of people. "Nobody knows what minimum level of antibodies is needed for protection. We just don't know whether people who have low but detectable levels of antibodies are protected or not. It's that uncertainty that justifies the need for a third dose, especially since we have these highly infectious variants that are capable of causing breakthrough infections even among healthy people," said Ali Ellebedy, PhD, Associate Professor of pathology and immunology, of medicine and of molecular microbiology. The US Centers for Disease Control and Prevention (CDC) recently recommended that people taking immuno-suppressants receive a third dose of the vaccine to strengthen their immune responses. The study showed that people taking anti-metabolites such as methotrexate, TNF inhibitors or JAK inhibitors, did not generate significantly weaker immune responses than people not taking those drugs. On the other hand, two classes of drugs were found to have particularly weakened immune responses. Only 65 per cent of people taking glucocorticoids and 60 per cent of people taking B cell-depleting therapies developed detectable antibody responses, the researchers said. /IANS