New Delhi: Some people who take the drug methotrexate to treat common immune system disorders like rheumatoid arthritis and multiple sclerosis may mount a weaker immune response to a COVID-19 vaccine, according to a study.People with immune-mediated inflammatory disorders are typically treated with drugs that reduce inflammation, including methotrexate.The disorders result when the immune system, meant to fight disease and drive healing, is triggered abnormally, which in turn causes inflammation, pain and swelling.The study, published in the journal Annals of the Rheumatic Diseases, looked specifically at patients' responses to the Pfizer-BioNTech mRNA COVID-19 vaccine, which the researchers measured by looking at the antibodies produced in.