No “Magic” in “New”: Immune Response to SARS-CoV-2 is More Characteristic than First Thought: More Encouraging Data

It appears protective immunity to SARS-CoV-2 may last at least 6 months and up to more than a year. Although the strain changes recently seen might be the reason for the rare re-infections recently reported, I believe it is more. The evidence for protective cross immunity with other CoVs and even bacterial antigens (pneumonia vaccines) rules (see earlier post) against the small genetic changes (D614G in the spike protein) in the spike protein inhibiting immunity. New data indicates that the mutation actually increases antibody neutralization https://www.medrxiv.org/content/10.1101/2020.07.22.20159905v2.full.pdf. I suspect that it is because the first viral infection was cleared early by interferon 1, IgA, and/or IgM, the latter which decline within 3 months. It is the IgG, particularly IgG3, that lasts longer: 7 months and the memory B cells even longer. But if infection response clears virus in less than 2 weeks, the IgG response never happens—opening up for reinfection. Researchers at Massachusetts General Hospital found IgG levels remained elevated for four months in those who recovered from COVID-19, and were protective neutralizing antibodies, which decreased over time. The researchers also showed that those infected with SARS-CoV-2 had immunoglobulin A (IgA) and immunoglobulin M (IgM) responses that were relatively short-lived, declining within about two and a half months or less, on average. https://immunology.sciencemag.org/content/immunology/5/52/eabe0367.full.pdf. Researchers at the University of Toronto discovered IgG antibodies were detectable for up to 115 days (approximately 4 months) in those recovered from COVID-19 https://immunology.sciencemag.org/content/immunology/5/52/eabe5511.full.pdf. University of Arizona focused on antibodies that bind to two different parts of the SARS-CoV-2 virus, most antibody tests look for antibodies at S1, which includes the receptor-binding domain by which the spike protein binds to a protein receptor to infect cells. But they also looked for antibody to the S2 region of the spike protein. They found SARS-CoV-2 antibodies in blood for at least 5 to 7 months, although they believe immunity actually lasts longer. They knew that people who were infected with SARS coronavirus-1, which is the closest relative to SARS-CoV-2, still show immunity 17 years after infection. If SARS-CoV-2 is anything like the first one, they expect antibodies to last at least two years, and it would be unlikely for anything less https://www.cell.com/immunity/pdf/S1074-7613(20)30445-3.pdf?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS1074761320304453%3Fshowall%3Dtrue.