La Jolla Institute researchers have a new study suggesting that people who have recovered from coronavirus may have lasting immunity for up to several decades. This was contained in the preprint of the findings published by the Cold Spring Harbor Laboratory.
Blood samples from patients who recovered months after initial infection have enough immune cells to prevent reinfection, according to results. While the paper is yet to be peer-reviewed, it is the first long-term study on coronavirus immune memory thus far.
"The amount of memory," explained virologist Shane Crotty, seems large enough to prevent the majority of recovered patients from severe disease. The study also suggests that with lasting natural immunity, vaccines may not be required yearly like the flu vaccine.
The team studied 185 coronavirus cases inclusive of 41 cases that have recovered for at least six months. An analysis of immune cells revealed that six months later, spike-specific memory B cells multiplied compared to a month after recovery. Meanwhile, two types of coronavirus-specific T cells (CD4+ and CD8+ T cells) "declined with a half-life of 3-5 months."
Immune cells remembering a virus is also called sterilizing immunity which doesn't happen often, said immunologist Alessandro Sette. When the immune system recognizes the virus, it could terminate the invader fast enough so that person doesn't experience symptoms nor becomes infectious.
Another study also looked at CD8+ T cells, which were detectable in up to 70% of Covid-19 patients. They compared the coronavirus-specific T cells before infection, after infection, and against influenza-specific CD8+ T cells. Results showed that even without detectable antibodies, the memory T cells from recovered patients may provide lasting immunity. Further research is needed to identify how and why CD8+ T cells are associated with coronavirus and post-recovery.
Immunologist Jennifer Gommerman explained that the reason why some patients may not have lasting immunity may be due to how much of the virus they were exposed to. Aside from viral load, there are other factors such as pre-existing health conditions, age, available treatment, and so on. These factors are important in vaccine development, said Gommerman, so that there won't be the same heterogeneity found in the infected population.
Waning immunity has been one of the main concerns with coronavirus. Researchers from Icahn School of Medicine at Mount Sinai reported in their study that up to 90% of mild and moderate cases have a strong antibody response that can protect the body for at least several months. Although the number of antibodies goes down after recovery, the body will produce a stable antibody response weeks or months after. Proof of this was found in donated plasma from recovered patients.
Jeffrey Shaman from Columbia University said that the study by La Jolla Institute has encouraging results. However, it is important to be mindful of the possibility of reinfection, although so far there have only been rare cases of Covid-19 reinfection. With coronavirus circulating less than one year, it is only in the next few years that researchers will be able to determine if antibodies and memory cells can provide lasting immunity.
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