Please go through the following links.
https://www.medrxiv.org/content/10.1101/2020.03.26.20044222v1.full.pdf
https://www.eurosurveillance.org/docserver/fulltext/eurosurveillance/25/10/eurosurv-25-10-3.pdf?expires=1586407115&id=id&accname=guest&checksum=2BFEC87E328D559EF2E441A53399132A
https://jamanetwork.com/journals/jama/fullarticle/2762452
It is possible if the patient didnt mount a sufficient antibody response or is compromised in some fashion after discharge. Life span of immunity is also unknown and fingers crossed its a long term immunity with a low mutagenic potential on Covid's part
With other coronavirus strains, experts say the antibodies that patients produce during infection give them immunity to the specific virus for months or even years, but researchers are still figuring out if and how that works with COVID-19.
No reinfection clearly documented in a recovered COVID-19 patient if we judge by symptoms, lab and radiological evaluation and contagiousness, not by CT-PCR results
It is not yet established that patients who are declared recovered from COVID-19 on the basis of two NEGATIVE RT-PCR tests for SARS-CoV-19 had actually recovered due to laboratory error of testing kits or the the positivity indicates a carrier state, as none of these reports indicated any worsening of clinical condition of the patient based on symptoms, CT-scan or other parameters (1). We have seen many patients with COVID-19 who despite making a clinical recovery are often having positive reports based on the RT-PCR results up to 35 days after initial diagnosis (2). There has been talk of viral RNA belong to dead virus (viral litter, debris) as the explanation for positive RNA-based PCR tests, as this test does not establish the presence of live virus.
Important point is that there is a disconnect between positive tests and the clinical condition of the such COVID-19 patients. If you follow up such patients, none of the patients had adverse outcome. 1.Preprint Clinical characteristics of the recovered COVID-19 patients ... 2. https://www.researchgate.net/post/What_are_the_interpretations_and_implications_of_having_negative_followed_by_positive_RT-PCR_tests_in_COVID-19_patients
Chance of reinfection in discharged COVID-19 patients is always there because the acquired protective immunity from SARS-CoV-2 infection is short-lived.
https://science.sciencemag.org/content/371/6529/eabf4063
https://www.nature.com/articles/s41591-020-1083-1
Also take a look at this useful RG link.
Article Epidemiologic characteristics of cases with reinfection, rec...