What the Immune Response Looks Like in Asymptomatic COVID-19 Cases

By Katelyn Jones

The world is currently in the middle of the COVID-19 pandemic, with over 16 million confirmed cases as at 26 July 2020. One of the reasons this pandemic is so hard-hitting is because people don’t fully understand the risks involved with asymptomatic cases. Researchers in China have conducted a study into these asymptomatic cases (where people are infected but show no symptoms like a cough, a fever or a headache) so that we can understand how to better control the spread of this virus and flatten the curve.

The researchers studied these asymptomatic individuals from the Wanzhou District in China to understand more about these 3 things:

  1. how long the individuals had the virus present in their system,
  2. for how long the individuals’ immune systems were protecting them after testing negative, and
  3. to understand more about the immune response of COVID-19 positive individuals.

They ran repeat RT-PCR tests, antibody titres and cytokine levels respectively to answer these questions.

Interestingly, the researchers found that the viral load between symptomatic and asymptomatic patients was similar but that the asymptomatic group shed the virus for longer (this doesn’t necessarily mean they were infectious for longer, but it could). This can be seen in the graph on the right. They also found that symptomatic cases developed a stronger immune response overall and that the antibody levels of their patients began to decrease within a few months of the study.

Lastly, the researchers determined that the asymptomatic group had a significantly lower inflammatory profile (a measure of how reactive or over-reactive your immune response is) than the symptomatic group, and the asymptomatic group’s inflammatory profile was similar to that of the healthy control group.

Overall, this shows that asymptomatic individuals have a weaker immune response than symptomatic individuals. It also advocates for social distancing and hand hygiene as asymptomatic individuals do still shed the virus, and for longer than symptomatic people.

Reference

  1. Long QX, Tang XJ, Shi QL, Li Q, Deng HJ, Yuan J, et al. Clinical and immunological assessment of asymptomatic SARS-CoV-2 infections. Nat Med. 2020.

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