Covid-19 immunity for most people may last more than eight months, potentially even years or decades, according to new research.
Researchers found that the levels of B and T cells, which are crucial to fighting off illness, remained stable up to eight months after initial infection.
The slow rate of decline also suggests these immune cells may persist in the body for long periods of time.
While the research has not been peer-reviewed or published in a scientific journal, the study is the most comprehensive and long-range look at the body’s immune response to coronavirus so far.
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Shane Crotty, a virologist at the La Jolla Institute of Immunology who co-led the new study, told the New York Times: ‘That amount of memory would likely prevent the vast majority of people from getting hospitalized disease, severe disease, for many years.’
Researchers took blood samples from 185 patients, between the ages of 19 to 81, who had tested positive for the coronavirus in the pandemic’s first months.
The US-based research team looked at four parts of the immune system, to build an overall picture of the immune response rather than individual components.
The parts were coronavirus antibodies, B cells that produce antibodies and two kinds of T cells which kill infected cells.
The scientists found that five months after the initial infection, ‘immune memory consisting of at least three immunological compartments was measurable in ~90% of subjects’.
This immune memory, consisting of various antibodies, was also found to be ‘durable’, declining very slowly – which is consistent with the possibility they might remain for years, or even decades.
These encouraging findings have been supported by evidence coming out of other research groups, such as immune ‘memory’ cells remaining for at least three months after coronavirus infection.
Last week, German researchers found that recovered Covid-19 patients also have protective ‘killer’ immune cells that exist even when antibodies are difficult to detect.
Leading immunologists suggest that these results all point towards the novel coronavirus acting as a ‘conventional’ disease, once the first few critical weeks have been passed.
Though a small number of patients were found not to have long-lasting immunity, possibly after being exposed to lower amounts of the virus, researchers have suggested vaccines would mean this isn’t a problem.
The high number of patients showing long term immunity also indicates vaccines may not have to be administered each year, as the flu vaccine currently does.
Recent studies have found that SARS survivors (closely related to the 2019 coronavirus) still carry immune cells more than 17 years after the first infection.
Though a recent study from Imperial College London found immunity to Covid-19 may decline over time, it’s not clear whether this will lead to patients being widely susceptible to reinfection.
Some immunologists suggest that comparisons to the common cold, another kind of coronavirus, are inaccurate due to the much larger amount of genetic variations, as compared to the novel coronavirus.
While others have noted it’s normal for antibody levels to drop over time, and that they form only one part of the immune system.