Wednesday 9 June 2021

Natural COVID-19 immunity may only last for 100 days


Research published in the journal BioMed Central finds that fewer than half of COVID-positive patients retained their disease fighting antibodies more than 100 days after infection (“IgG and IgM antibody formation to spike and nucleocapsid proteins in COVID-19 characterized by multiplex immunoblot assays”). Such research is important in terms of assessing just how long natural immunity against the coronavirus disease may continue for.


By natural immunity, this is the immune response that takes place following exposure to the virus (as opposed to the vaccine). The extent of natural immunity to a given disease lasts for different periods of time according to a specific disease. For example, to measles this is for decades.


The response to SARS-CoV-2 virus is, in contrast, similar to seasonal flu, and the natural immunity lasts for less than a year. This is based on pulling data from a large study, undertaken from multiple academic institutions.


The data indicated that 44 percent of people studied, diagnosed with mild-to-moderate COVID-19, continue to express antibodies beyond day 100. However, 56 percent of people lost virus neutralizing antibodies within a few months.


Loss of immunity and more viral spread


The loss immunity may explain the timing of successive waves of the disease, as with the surge in cases during autumn 2020.


The information was drawn from an analysis of COVID-19 ImmunoBlot (IB) assays. Such assays were developed for detecting IgG and IgM antibodies to SARS-CoV-2 virus proteins in COVID-19 patients.


The specificity of the IB assay was established with 231 sera from persons with allergy, unrelated viral infections, autoimmune conditions and suspected tick-borne diseases, and 32 goat antisera to human influenza proteins.


Easing lockdown measures?


Going forwards, further studies are underway to assess the long-term immune response for both natural immunity and vaccine immunity. With the vaccine, antibodies last for six months or longer following a second dose (thereby suggesting that vaccine immunity is double that of natural immunity).


These inquiries into immunity are important for assessing how long protection lasts for in relation to the general population interacting with others during the pandemic. In time this may enable decisions to be taken about the future of social distancing and wearing a mask.


Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (

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