When individuals are affected by a viral infection, they usually develop immunity to that particular strain of the virus. They may develop partial immunity to another strain of the same virus but the individuals are not completely protected against the second strain of the virus. For this reason, common cold can occur a few times in the same season. Similarly, influenza recurrence can also occur when infection occurs due to a different strain the second time.
There has been a similar concern with COVID-19 if it can cause reinfection in the individuals who are already affected by it. There was a case report published in International Journal of Infectious Diseases that described a case where a confirmed COVID-19 patient had two negative tests before isolation was removed. However, on further follow-up, the patient tested positive again in five days. The patient continued to get better and did not have any worsening symptoms. More than reinfection, this case illustrates that COVID-19 testing produces several false results.
Similarly, there were other cases reported where patients had positive COVID-19 test after recovering from the illness previously. Few patients also had fever again after being discharged from the hospital. In most cases, recurrent fevers and recurrent positive tests were attributed to superadded bacterial infections. Viral shedding can occur for 3 weeks after the symptoms resolve. However, viral shedding is not equivalent to infectivity or the ability to infect other healthy individuals. COVID-19 test uses a technique called as Reverse Transcription Polymerase Chain Reaction (RT-PCR). RT-PCR can be positive if there are any viral particles in the samples. Even if the virus is not intact and even if the viral particles cannot infect other healthy individuals, RT-PCR can still be positive. Positive test results after recovering from COVID-19 creates confusion as the positive test does not differentiate if the individual is infective or not.
A study which is not peer reviewed yet researched if rhesus macaques (a type of monkey) can be reinfected with COVID-19. In this study, monkeys were infected with SARS-CoV-2. After the symptoms were alleviated, antibodies were tested to check for immunity. These monkeys were rechallenged with the same dose of SARS-CoV-2. On further follow-up, viral tests, imaging studies and pathological tests showed no recurrence of COVID-19. This study concluded that the COVID-19 infection could protect from subsequent exposures.
In summary, based on the evidence available, reinfection with SARS-CoV-2 may not happen. However, as the pandemic evolves, things may change. There is a concern that there are two types of SARS-CoV-2 – L type and S type. It is unclear if reinfection can happen with one type if the initial infection was due to a different type. Further research may be needed.
Chen D et al. Recurrence of positive SARS-CoV-2 RNA in COVID-19: A case report. Int J Infect Dis. 2020 Mar 5;93:297-299. doi: 10.1016/j.ijid.2020.03.003.
Lan L, Xu D, Ye G, et al. Positive RT-PCR Test Results in Patients Recovered From COVID-19. JAMA. Published online February 27, 2020. doi:10.1001/jama.2020.2783
Zhou L et al. Cause analysis and treatment strategies of "recurrence" with novel coronavirus pneumonia (covid-19) patients after discharge from hospital. Zhonghua Jie He He Hu Xi Za Zhi. 2020 Mar 2;43(0):E028. doi: 10.3760/cma.j.cn112147-20200229-00219.