This study, just published in Clinical Infectious Diseases on Wednesday, presents antibody test results for >2500 healthcare workers and first responders infected with SARS-CoV-2 in March-April in NYC and Detroit, who are now >6 months out from infection.
The results found that almost 95% still had evidence of SARS-CoV-2 antibodies in their blood after 6 months -- including 100% of those who had been hospitalized and even nearly 90% of those with asymptomatic infections. There are several variables associated with likelihood of SARS-CoV-2 antibodies, with those taking immunosuppressive drugs less likely to have antibodies after 6 months, and minorities, obese, and those with most severe symptoms more likely to have antibodies after 6 months.
This should reassure those who have become alarmed by some recent discussion worrying that there is no long-term immunity from SARS-CoV-2 after infection -- this is the first published study I've seen in which the subjects are 6 months out from time of infection.
My own opinion based on the preponderance of evidence in the literature has been that while there have been individual anecdotes of reinfections in <6 months, the exceeding rarity of these suggests statistically that a VAST majority of those infected have reasonably long term immunity. This study provides support for that viewpoint.
This is good news for the prospect of an effective vaccine. We still have much to learn about the immune response to SARS-CoV-2, but this is encouraging.