The chances of immunity against SARS-CoV-2 after recovery from COVID-19 are very high.
Current studies on immunity after past disease (as of September 09, 2020)
According to a study conducted at Mount Sinai Hospital in New York on more than 1,300 recovered COVID-19 patients, over 99% of them have produced IgG antibodies. The number of antibodies produced was independent of age, sex, and severity of the disease. The ELISA test used also detects antibodies against the spike protein, which is our test’s target antigen. (https://www.medrxiv.org/content/10.1101/2020.04.30.20085613v1).
With the help of this test, Mount Sinai Hospital also identified potential plasma donors, whose plasma can be used to treat severely ill COVID-19 patients. (https://www.medrxiv.org/content/10.1101/2020.05.20.20102236v1.full.pdf+html)
In a recent study, published in the peer-reviewed journal Cell, 13 of 14 patients that recovered from COVID-19 showed antibodies against the spike protein of the novel coronavirus. The sera of these 13 patients showed anti-viral effects in so-called neutralization assays. This type of cellular assay is considered to be proof that the patients’ antibodies can neutralize the novel coronavirus. (https://www.cell.com/immunity/pdf/S1074-7613(20)30181-3.pdf)
Studies at the French Institut Pasteur came to comparable results. From 160 previously positively tested clinic employees, antibodies against the spike protein could be detected in 159 persons after an average of 24 days. Also in this study, the function of the antibodies was checked in neutralization tests and confirmed in 98% of the samples. (https://www.medrxiv.org/content/10.1101/2020.05.19.20101832v2.full.pdf)
First data of a clinical Phase I/II study for the development of a SARS-CoV-2 vaccine shows a clear correlation between the production of IgG antibodies against SARS-CoV-2, their neutralizing effect, and the protection against new infections in NHPs. (https://www.biorxiv.org/content/10.1101/2020.04.17.046375v1.full.pdf).
On August 25, 2020, after more than 27 million infections worldwide, the first case of reinfection was reported. The study was published in the journal “Clinical Infectious Diseases”: https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1275/5897019. 142 days after the first infection, the patient was again tested positive for the novel coronavirus upon arrival in Hong Kong. The second infection was asymptomatic.