Furthermore, they discovered that the tests were most accurate when utilized within the first week after symptoms appeared. Antigen testing properly ruled out infection in 99.5 percent of patients with COVID-19-like symptoms and 98.9 percent of those without symptoms who did not have COVID-19. The researchers also found that people can be virus-free for up to seven days after showing symptoms. Home test kits have become increasingly popular as countries try to limit the spread of COVID-19. However many studies have shown that these tests have low accuracy for two main reasons: first, because the tests only look for antibodies rather than actual living viruses; and second, because people with lung problems, like Asthma or COPD, may not be able to produce enough antibodies to be detected by the test. A study conducted by the Chinese Center for Disease Control and Prevention showed that among 514 patients with confirmed COVID-19, the sensitivity of commercial antibody tests was only 44.6% while the specificity was 100%. The same study reported that among 169 patients without COVID-19 diagnosis but with other respiratory infections, the sensitivity was only 22.1%. In conclusion, home test kits have poor accuracy and cannot be used to diagnose current infection or determine vaccine efficacy.