People previously infected with COVID-19 were more likely to experience fatigue, headache, chills, fever, and muscle and joint pain after the first shot of the COVID-19 vaccine than people who had never been infected, according to a new study. The researchers at Mount Sinai found much higher antibody levels after both the first and second doses of the vaccine in people with prior COVID-19 infections. Based on their data, the researchers believe you might only need one shot if you have already had the virus. Likewise, another study from the University of Maryland found that people previously infected generated antibody levels after one dose that were as high as after the second dose in people who had never been infected. What is hard to know yet is how effective one dose of the vaccine would be for people who only had mild cases or were asymptomatic, as they might not have as much immunity from that infection.