An initial study suggests that immunity to COVID-19 can last for at least 6 months – and possibly longer, potentially even a few years, when all components of the body’s immune memory are taken into consideration.
Many previous studies have focused on the antibodies and protein composition of the immune system with some studies suggesting that immunity lasts only a few months.
However, this new study, that has not been peer-reviewed or published in the scientific journal, has analyzed multiple compartments of immune memory over time: antibodies, B cells and T cells, among other features of immune memory.
The study included 185 adults, ages 19 to 81, in the United States who had recovered from Covid-19. Most of the adults had mild disease.
The research team comes from the La Jolla Institute of Immunology, University of California, San Diego, and the Icahn School of Medicine at Mount Sinai. They analyzed blood samples from patients at various stages from the moment the symptoms appeared.
In the blood samples, the researchers examined components of immune memory. They found that antibodies “were durable” with only “modest declines” emerging at six to eight months, but noted that there was about a 200-fold range in the level of antibody responses among the adults.
The researchers have also found that Memory B cells have been found in most cases of COVID-19, and it appears that the number of memory B cells increases with time.
“B-cells for some infections can persist for a long time, including more than 60 years after getting the smallpox vaccine, or more than 90 years after getting the flu,” the report says.
The researchers found two types of T cells and the data suggested that “T cell memory might reach a more stable plateau, or slower decay phase, later than the first 6 months post-infection”.
However, this study still has many limitations, requiring more studies on a larger scale to see if similar findings have been identified.
According to Lawrence Young, Professor of Molecular Oncology at the University of Warwick, who was not involved in the study, commented that “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”.
Compared to initial thought, this study shows that immune responses can be sustained longer, sparking hope for an effective vaccine and a sustained immunity.
In viruses, some diseases can achieve lifelong immunity. But respiratory viruses like the flu tend to mutate, and people can get it again and again.
So, vaccines for these diseases provide only partial protection against serious infections and illness.
The coronaviruses seem to lie in the middle. Seven types of coronavirus are found to be contagious to humans, including SARS-CoV-2.
Many human coronaviruses can cause the common cold, but since they are usually not lethal, they have not been thoroughly studied.
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