Researchers at a US hospital in Boston have identified a group of patients who have quickly recovered from Covid-19 and display indications of having longer-lasting immunity.
This group of “antibody sustainers” had disease symptoms over a shorter period, “suggesting that some individuals who recover from Covid-19 faster may be mounting a more effective and durable immune response to the virus”, according to the medical team based at Brigham and Women’s Hospital.
The findings may help answer one of the most perplexing questions about the virus: how long does immunity last?
A key indicator of immunity is the presence of virus-specific antibodies but previous studies have provided conflicting accounts about whether people who have recovered from infection can sustain potentially protective antibodies or not.
The study led by BWH investigators examined blood samples and cells from patients who had recovered from mild to moderate Covid-19 and found that while antibodies against the virus declined in most individuals after disease resolution, “a subset of patients sustained anti-virus antibody production several months following infection”.
Their results are published in the latest issue of the journal Cell.
"We've found a subset of individuals that heal quickly while sustaining virus-specific antibody levels after Covid-19," said Dr Duane Wesemann, an immunologist and physician at BWH who is also an associate professor at Harvard Medical School.
“The kind of immune response we’re seeing in these individuals is a bit like investing in an insurance policy – it’s the immune system’s way of adding a potential layer of protection against future encounters with the virus,” he said.
The team collected and analysed blood samples monthly, measuring a range of antibodies, including immunoglobulin-G (IgG), against the virus. A total of 92 people in the Boston area who had recovered from Covid-19 between March and June were assessed – five were hospitalised but all others recovered at home.
The team found IgG levels against the virus tended to decline substantially in most individuals over three to four months. In about 20 per cent of individuals, antibody production remained stable or enhanced over the same time period.
“Sustainers” had symptoms for a significantly shorter period of time compared to “decayers”; an average of 10 days versus 16 days. They also had differences in memory T cell populations and B cells – types of immune cells that can play a key role in “immune memory” and protection.
An important limitation of the study, the team accepts, was most involved were adult white women. Future research, it suggests, must aim to enroll a more diverse population to further elucidate whether variations in immune response exist across people of different ages and ethnic and racial backgrounds.
Significantly, they note further research may help determine whether similar dynamics of immune response are also seen in people with asymptomatic and severe disease.
“The data point to a type of immune response that’s not only adept at handling viral disease by leading to a swift resolution of symptoms, but also better at producing cells that can commit to longer-term production of anti-virus IgG antibodies,” Dr Wesemann explained.
“Figuring out how these individuals are able to support longer-term antibody production is relevant to Covid-19, and will also have important implications for our understanding of the immune system in general,” he believed.