- According to researchers, our immune systems' response to Covid-19 is complex.
- Some patients have become reinfected due to a deficient immune response.
- More data is needed, but this phenomenon could help to better understand reinfection.
As Covid-19 spreads, many experts are questioning the validity of the herd immunity theory. Researchers are asking whether it will be possible to stave off Covid-19 as more people develop antibodies.
While previous research has shown that recovery from Covid-19 is associated with a production of antibodies against SARS-CoV-2, it is still uncertain whether these antibodies can provide long-term immunity.
There is also the ongoing question of Covid-19 reinfection – where people test positive twice for SARS-CoV-2. Although the phenomenon is not well understood at this stage, reinfection could lead scientists to an effective vaccine and better treatment.
Case study points towards a flaw in immune system
In a recent pre-print case study that appeared on the database medRxiv, a team from the University of Washington investigated a case that suggests a poorly developed immune response and waning antibody levels could make people more susceptible to reinfection.
The case study refers to a care-home resident in their sixties who tested positive for SARS-CoV-2 after developing severe pneumonia. After more than a month in hospital, the patient tested negative.
In July, however, the patient tested positive again – this time with much milder symptoms, including a slight cough and shortness of breath.
According to Jason Goldman, who led the study, this was definitely a case of two separate infections, as opposed to viral shedding from the initial infection. Goldman and his team found that the patient produced extremely low levels of antibodies against the virus after testing positive again.
They suspect the first infection also yielded only a low dose of antibodies, which explains the reinfection.
Humoral immunity investigated
While the patient produced antibodies in the first week of reinfection, there was no evidence that the antibodies helped block SARS-CoV-2.
The researchers also looked at the so-called B cells – the memory cells that are meant to "remember" a previous infection in the long term to fight it – and found that no new clones of these cells had emerged after several days from reinfection.
According to the researchers, this suggests a deficiency in developing a response to the reinfection, which could have important implications for vaccine development.
The researchers are, however, optimistic that the patient's infection was milder the second time around, even though there has been a case where reinfection was more severe.
These humoral immunity levels (antibody-mediated immunity) could provide a strong starting point for experts to describe a benchmark which is shown not to be effective against reinfection, the authors wrote.
But more research from a larger case series of reinfected patients will be needed before this immune response is fully understood.
READ | Three things scientists still need to learn about Covid-19 reinfections
READ | Covid-19: Understanding immunity and what it means for a vaccine
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