M a n u s c r i p t Dear Editor: Current reports, including the work by Zhao J et al [1] , on antibody testing have found that positive antibodies can be detected in all COVID-19 patients [1, 2] . Therefore, more and more studies recommend nucleic acid detection combined with antibody detection for the diagnosis and monitoring of COVID patients [1, 3] . However, there is no confirmed evidence to prove whether all COVID-19 patients can produce antibodies. Here, we reported a cases of negative antibody test after virus infection. Zhao J et al reported that the median seroconversion time for Ab, IgM and then IgG were day-11, day-12 and day-14, separately and antibody continued to be 100% positive at least on day 39 [1] . Wölfel R et al also reported that seroconversion occurred in all patients after 14 days [2] . This patient's course of antibody testing had exceeded the median seroconversion time by 2 times but still in the positive duration.
Therefore, we believed that the patient's body did not produce antibodies to the
A c c e p t e d M a n u s c r i p t Of course, the possibility of low viral load below the detection limit of conventional methods cannot be completely ruled out [4, 5] . Or it is due to the limitation of testing specimens, because some studies suggest that positive rates of different specimens were different [6] .
There are maybe several reasons to explain why the body cannot produce antibodies after being infected by SARS-Cov-2. Firstly, the SARS-CoV-2 maybe was mutated, resulting in production of special antibodies that cannot be detected by conventional methods. Secondly, the patient was unable to produce antibodies due to a certain undiscovered immunodeficiency, although there is currently no evidence.
Because a case reported found that antibody responses against SARS-CoV-2 in a HIV-1-infected patient were delayed [7] . These speculations still need to be further verified.
This case indicated that specific antibodies may be negative in some patients after being infected with the SARS-CoV-2.
The serum SARS-CoV-2 IgM and IgG antibodies of the patient were detected using a sandwich enzyme linked immunosorbent assay (ELISA kit, Zhuhai Livzon Diagnostics Inc., Zhuhai, China) according the to the manufacture's instructions. M a n u s c r i p t 