COVID-19: Quicker recovery may indicate long-term immunity
Researchers recently found that some people who recovered quickly from COVID-19 continued to have antibodies against SARS-CoV-2 for several months. This discovery suggests the potential for long-term protection among those with a strong initial immune response.
According to the Centers for Disease Control and Prevention (CDC), there have been more than 9 million confirmed COVID-19 cases in the United States since January 2020.
With that number increasing every day, scientists remain focused on uncovering how the immune system responds to SARS-CoV-2, which is the virus that causes COVID-19, to combat it successfully.
Researchers have been investigating key questions surrounding immunity to SARS-CoV-2 since it first appeared, including how long protection from the virus lasts after recovery and whether or not the severity of the symptoms affects that immunity timeframe.
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Uncovering these factors may influence the way in which scientists develop effective treatments and vaccines. It may also indicate whether or not herd immunity is possible.
A critical indicator of sufficient immunity to any viral illness is the presence of virus-specific antibodies. In SARS-CoV-2, conflicting evidence exists as to whether or not there is long-term protection from the virus after recovery.
To shed more light on this matter, investigators sought to measure antiviral antibodies in a group of volunteers recovering from COVID-19.
Uncovering immunity
Researchers from Brigham and Women’s Hospital in Boston, MA, led the new study. Its results now appear in the journal Cell.
The scientists examined blood samples and cells from people who had recovered from a mild-to-moderate case of COVID-19.
Although most individuals experienced a decline in anti-SARS-CoV-2 antibodies, a small group of individuals retained antivirus antibodies for several months.
To conduct the research, the team recruited 92 individuals from the Boston area — mostly adult white women — who had recovered from a confirmed case of COVID-19 between March and June of this year.
Five people in the study were hospitalized, but all the others experienced mostly mild symptoms. The scientists collected blood samples when the symptoms resolved, and after this, they took repeated blood tests at monthly intervals.
After measuring virus-specific immunoglobulin G antibodies over 3–4 months, the team found that while most showed a decline in these immune markers, 20% of the volunteers had sustained or even enhanced antiviral antibody production during that timeframe.
The participants who retained antibodies had previously experienced a shorter duration of COVID-19 symptoms, averaging around 10 days, versus those who had a more prolonged bout of the illness, at around 16 days.
The group with sustained anti-SARS-CoV-2 antibodies also showed key differences in CD4+ T cell subsets that persisted after recovery, along with other immune cells that foster immune memory and long-term protection.
This finding indicates that a proficient immune response, which results in a rapid resolution of symptoms, could also play a role in how long immunity lasts.
“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.”
– Study lead Dr. Duane Wesemann, Ph.D.
Evidence from previous studies
Scientists do not yet fully understand the body’s immune response to the novel coronavirus.
However, in an article from September 16, 2020, the study authors reveal how the immune system mounts an attack against this novel virus, and how that may play out in symptom severity and extended immunity.
After examining the three major lymphocyte types — B cells (antibody-producing cells), T cells (killer cells), and helper T cells — and comparing these data with COVID-19 symptom severity, they conclude that when all three lymphocyte types were adequately activated, with a robust T cell response, people fared better than when there was an uncoordinated adaptive immune response.
Therefore, the study authors suggest that a coordinated attack by the immune system, especially T cells, may reduce the severity of the illness and foster enhanced long-term immunity.
Study limitations and research goals
Because the new research used mostly adult white women as volunteers, the team notes that analyzing a more diverse population — to assess whether or not these immune responses are the same in people from different age groups and racial backgrounds — is warranted.
Also, expanding the research to include asymptomatic individuals and those with severe illness may offer more insight into how long immunity lasts after acquiring and recovering from COVID-19.
Once scientists know that, they can develop more targeted treatments and vaccines, with herd immunity as the goal.
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