Since its discovery, more than 37 million people have been infected by SARS-CoV-2 with deaths around 1 million worldwide . The prevalence is not known because infected individuals may be asymptomatic . In addition, the use of specific diagnostic tests is not always conclusive, raising doubts about the etiology of the disease . The best diagnostic method and the ideal time of collection remains the subject of study . The gold standard for diagnosing COVID 19 is the RT PCR molecular test, usually using an oropharynx and nasopharynx swab . Its sensitivity is 70% and drops significantly after the second week of symptoms . Serological tests, in turn, have increased sensitivity after 14 days, and can contribute to the diagnosis when SARS-CoV-2 infection is suspected, even with negative RT PCR . Our study showed sensitivity and specificity of 100% of the serological test (ELISA method) for cases of viral pneumonia caused by the new coronavirus, suggesting that this test could assist in the diagnosis of pulmonary interstitial changes that have not yet been etiologically clarified . We found a greater immune response in men, regardless of the severity of symptoms . The greater the severity, the higher the levels of IgA and IgG, mainly found in patients with multilobar impairment and in need for oxygen . We concluded that the serological test collected around 30 days after the onset of symptoms is the best diagnostic tool in the convalescence phase, not only for epidemiological purposes, but also for the etiological clarification of pulmonary changes that have not yet been diagnosed.