A preprint, an unpublished non-peer reviewed study, posted on bioRxiv looks at immunological memory to SARS-CoV-2 over six months after infection.
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, said:
“This preprint has yet to be peer-reviewed but brings exciting news. The immune system is more than just antibodies in the blood and these authors have carefully measured different types of antibodies and different types of immune memory cells to see how long immunity lasts. They identify particular types of memory B cells and memory T cells which are still present in good quantities six to eight months after infection. In fact, the cells continued increasing for two or three months after symptom onset. So even if the levels of antibody in the blood go down, there are cells standing by ready to make new ones if needed.
“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.”
Prof Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said:
“This paper makes it clear that there are different components in the immune system that are relevant to provision of the body’s response to SARS CoV-2. They show that some components seem to show relatively little decline in their levels over the time periods so far studied. Some pessimists have focused on decline in antibody levels, but it has often been pointed out that they are not the only important component of immune response.
“The paper seems to be of a high standard in spite of not being peer-reviewed. Some of the statistical methods used, while common in this field, are not as appropriate as the best statistical methods, but as far as I can see the better methods would probably reach the same overall conclusions. They show a great deal of their data clearly.
“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. 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.”
Dr Alison Whitelegg, on behalf of the Association for Clinical Biochemistry and Laboratory Medicine (ACB) Immunology Committee, said:
“In contrast to some reports of waning antibodies, the authors detect the actual antibody-producing cells months after infection and, by looking at the overall immune response to SARS-Cov-2, go on to hypothesise what a repeat infection and resulting immune response would look like – a mild or asymptomatic infection in general population. The only limitation from this study is the method of collection of data as only one time point was used for the vast majority of individuals.”
Prof Lawrence Young, Professor of Molecular Oncology, University of Warwick, said:
“Understanding the dynamics and longevity of the immune response to SARS-CoV-2 is crucial to determining whether herd immunity is possible and how any vaccine might provide long-term protection from COVID-19. This study provides a detailed examination of both antibody and T cell-mediated responses to the virus. It shows that the majority of infected individuals maintain neutralising antibody responses for more than six months after the onset of symptoms. This observation is supported by the demonstration that antibody-producing B cells increase over the six month period while T cell responses decline.
“Overall, this is an important study confirming the existence of immune memory to SARS-CoV-2 but with a degree of variation from person to person. This variation might be due to some individuals having had very low-level asymptomatic infection. It might be expected that those previously infected individuals with a low immune memory response would be susceptible to re-infection with SARS-CoV-2. But the significant take home message is that the immune response to the virus is more long-lived than previously thought, and this lets us continue to hold hope that an effective vaccine will be able to induce sustained protective immunity.”
‘Immunological memory to SARS-CoV-2 assessed for greater than six months after infection’ by Jennifer M. Dan et al. was uploaded to bioRxiv on 16th November 2020.
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