COVID-19 Vaccines May Not Be Effective In This Group Of Americans By Danielle Ong on May 19 2021 12:21 PM Less than 60 percent of US adults have received at least one Covid vaccine injection, and authorities are scrambling to convince the rest to do so AFP / Angela Weiss COVID-19 vaccines may not work fully or at all in 3% of the population in the United States, new research showed. Early data suggests that the vaccines offer a weaker response in people who take immunosuppressive drugs and, potentially, steroids. Immunocompromised Americans -- which make about 3% to 4% of the U.S. population -- may not be protected against the novel coronavirus despite being fully vaccinated. According to the research, 15% to 80% of people with underlying medical conditions, including specific blood cancers or previously organ transplants, are generating fewer antibodies, The Washington Post reported.