Asymptomatic COVID-19 findings dim hopes for ‘herd immunity’ and ‘immunity passports’

(Emily Chung, Christine Birak, Marcy Cuttler/ CBC News) — A closer look at people who tested positive for COVID-19 but never developed symptoms has found that such asymptomatic carriers have few to no detectable antibodies just weeks after infection, suggesting they may not develop lasting immunity.

There’s growing evidence that a significant proportion of people who test positive for COVID-19 never show symptoms, although it’s not clear what percentage of people that is and what role they play in spreading the disease.

A Chinese study published this week in Nature followed 37 people in Wanzhou District in China who did not show any outward signs of the disease, despite testing positive when their respiratory tracts were swabbed and being kept in hospital for observation.

Some key findings include:

  • Levels of antibodies against COVID-19 were significantly lower in asymptomatic carriers than those with symptoms during active infection.
  • Antibody levels also dropped off far more quickly in people who never showed symptoms, and 40 per cent of them had no detectable antibodies eight weeks after recovery, compared with 13 per cent of symptomatic patients. (…)
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