A large new study from Iceland suggests that antibodies against SARS-CoV-2, the coronavirus that causes Covid-19, last for at least four months in most people.
There’s been much debate about immunity, antibodies, and Covid-19 — and there is still much more to find out. However, unlike some previous studies, the new research reassuringly shows that some level of meaningful immunity to Covid-19 can be achieved in some people for at least four months. The study's findings are published in the New England Journal of Medicine.
Iceland has been prolific in its Covid-19 screening, testing around 15 percent of the Nordic country’s whole population. Taking advantage of this plentiful testing, scientists looked for antibodies in blood samples taken from over 30,500 people in Iceland (over 8 percent of the nation’s population).
They found that over 91 percent of the 1,797 people who recovered from Covid-19 in Iceland tested positive for antibodies. On top of that, a subgroup of almost 2,000 people showed that levels of virus-specific antibodies appeared to remain stable for at least four months after initial diagnosis. They also discovered that antibody levels continued to increase over the first two months and then plateaued over the next two months.
“We are pleased to be able to put to rest the concern that the titer of the antiviral antibodies may decline within weeks of infection," Kari Stefansson, senior author on the paper and CEO of deCODE genetics, a private biopharmaceutical company closely affiliated with the research, said in a statement.
All of this sounds pretty promising. However, other researchers were quick to point out that apparent immunity to a novel disease can be a fickle thing. For starters, immunity is not simply a case of antibodies; the immune response to a pathogen also relies on a well-trained army of B cells (the white blood cell that secretes antibodies) and T-cells (which directly kill cells that have been infected by an invader).
Previous studies have not shown such an optimistic picture. A study in May found that people who experienced a mild case of Covid-19 lose their antibodies more rapidly than those who are severely ill, concluding levels of neutralizing antibodies decreased by 81 percent in asymptomatic patients, compared to 62 percent in symptomatic patients eight weeks after the illness had resolved. The study also doesn't address recent evidence that appears to show people can become reinfected with Covid-19.
Another limitation of the research is that Iceland is a unique and homogenous society with a small population derived from a largely single ethnic and geographic origin, which means the findings of their screening might not necessarily reflect the situation in other countries.
However, while the nature of immunity to Covid-19 remains hazy, this new research from Iceland does provide some hope that meaningful immunity to Covid-19 is possible.
"The most striking observation was that antibodies remained stable over the four months after diagnosis... Unlike previous studies, this study suggested stability of SARS-CoV-2 humoral immunity," two independent researchers from Harvard University and the US National Institutes of Health, who were not directly involved with the study, wrote in a commentary article released alongside the study.
“Whether antibodies that persist confer protection and retain neutralizing or other protective effector functions that are required to block reinfection remains unclear," the duo added.