Good question. Ordinarily I would say that the fact that you're even asking is totally ridiculous, but the narrative has actually been spread that herd immunity

Good question. Ordinarily I would say that the fact that you're even asking is totally ridiculous, but the narrative has actually been spread that herd immunity is a myth for COVID-19 - which is false - so I absolutely understand your question. Unfortunately there are literally factions out there trying to convince people that this thing is impossible to build immunity to, which again is false. Have some studies: ["Neutralizing and binding antibody kinetics of COVID-19 patients during hospital and convalescent phases"](https://www.medrxiv.org/content/10.1101/2020.07.18.20156810v1.full.pdf https://www.medrxiv.org/content/10.1101/2020.07.18.20156810v...) - Published July 18 2020 - Based on these half-life data, we estimate that the median times for IgM, IgA and IgG to become seronegative are 4.59 (IQR 4.12-5.03), 7.78 (IQR 6.71-9.16) and 42.72 (IQR 33.75-47.96) months post disease onset. - This study suggests that SARS-CoV-2 infection induces robust neutralizing and binding antibody responses in patients and that humoral immunity against SARS-CoV-2 acquired by infection may persist for a relatively long time. ["SARS-CoV-2 infection induces robust, neutralizing antibody responses that are stable for at least three months"](https://www.medrxiv.org/content/10.1101/2020.07.14.20151126v1.full.pdf https://www.medrxiv.org/content/10.1101/2020.07.14.20151126v...) - July 17, 2020 - Here we report that the vast majority of infected individuals with mild-to-moderate COVID-19 experience robust IgG antibody responses against the viral spike protein, based on a dataset of 19,860 individuals screened at Mount Sinai Health System in New York City. - We also show that titers are stable for at least a period approximating three months, and that anti-spike binding titers significantly correlate with neutralization of authentic SARS-CoV-2. Our data suggests that more than 90% of seroconverters make detectible neutralizing antibody responses and that these titers are stable for at least the near-term future. -------- BTW, there's something called immunological memory, your memory B/T cells persist for decades. So even if you, say, were only fully immune to reinfection for 1 week, you could still get to herd immunity by building up enough immunological memory since the presence of memory B/T cells will reduce transmission. Anyway, fortunately COVID-19 produces immunity of several months at least.