While the longevity of immunity against covid-19 post infection continues to be an area under continuous research, a new study has indicated that the protection may last more than six months. The research, yet to be peer-reviewed or published in a scientific journal, done by the scientists from the La Jolla Institute for Immunology, University of California, San Diego, and Icahn School of Medicine at Mount Sinai – studied the multiple compartments of adaptive immunity against covid-19 in 185 covid-19 cases, including 41 cases at more than 6 months post infection.
The ages of the subjects having recovered from covid-19 ranged from19 to 81 in the United States. Most of the adults had a mild disease and didn’t need any hospitalisation. The researchers analyzed blood samples collected at various ahses of the disease following the onset of symptoms, with some collected more than six months later.
The scientists said that understanding immune memory to SARS-CoV-2 is critical for improving diagnostics and vaccines, and for assessing the likely future course of the pandemic. Humans make SARS-CoV-2-specific antibodies, CD4+ T cells, and CD8+ T cells in response to SARS-CoV-2 infection. The authors claimed that this is the first study of its kind, incorporating antigen-specific antibody, memory B cell, CD8+ T cell, and CD4+ T cell measurements, out past 6 months post-infection.
Examining the components of immune memory, the scientists found that that antibodies were “durable” with only “modest declines” emerging at six to eight months. The researchers said that there was about a 200-fold range in the level of antibody responses among the adults.
The scientists detected B cells in almost all covid-19 cases. The researchers said there appeared to be an increase in memory B cells over time. “B cell memory to some other infections has been observed to be long-lived, including 60+ years after smallpox vaccination, or 90+ years after infection with influenza,” the authors said.
They also identified two types of T cells. “T cell memory might reach a more stable plateau, or slower decay phase, later than the first 6 months post-infection,” the study states. The researchers however said that more research is needed to determine whether similar findings would emerge among a larger group of people across more time points.
“The paper confirms the importance of looking at memory B cells and memory T cells in order to assess immunity and shows the best types of memory cells to look for and the best time to look for them. It gives us hope that immunity to SARS-CoV-2 could last for several years,” said Prof Deborah Dunn-Walters, Professor of Immunology at University of Surrey and Chair of the British Society for Immunology expert advisory group on covid-19 Immunology.
In a statement to UK based Science Media Centre, Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said that there are two major consequences if the findings are as they say. “Firstly, although most of the cases described here had mild disease, it looks as though their immunity to a second infection is reasonably high. Most infections do lead to mild disease, especially in middle-aged and younger people. This means that the population level of immunity may be rising which will eventually lead to reduced transmission,” Evan said adding that this, coupled with immunity being conferred by vaccination, offers prospects of transmission of the virus being markedly reduced over the next year or so.
“Secondly, it is probably very good news for vaccines also being able to provide immunity that is more than very short-term. We do not know that for certain yet, but it is encouraging,” said Evans.
Globally, scientists have been studying the immunity response among people infected with covid-19. A recent study published in the Science Journal also showed that people infected with covid-19 were found to have antibodies for five months. Similarly, the results of two recent studies, published in the journal Science Immunology showed that people who survive a Covid-19 infection continue to produce protective antibodies against key parts of the virus for at least three to four months after developing their first symptoms. Various previous studies have shown that immunity against covid-19 can last for around six months.
Earlier this month a Research from the UK Coronavirus Immunology Consortium (UK-CIC), Public Health England and Manchester University NHS Foundation Trust indicated that a robust cellular (T cell) immunity against SARS-CoV-2 is likely to be present within most adults six months after primary infection.