Seroprevalence of SARS-CoV-2 antibodies three times higher than reported cases

The actual number of Sydneysiders infected with SARS-CoV-2 may have been 3.5-times greater than reported infections, a study has estimated.

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11 November

• Australian seroprevalence study suggests COVID-19 infections more than three times higher than reported.
• Latest confirmed COVID-19 infection numbers from around Australia.

• The actual number of Sydney residents infected with SARS-CoV-2 may have been 3.5-times greater than reported infections, a study has estimated.
  The study, published in the Medical Journal of Australia, tested 5,339 specimens collected in Sydney between April and June 2020 from women undergoing antenatal screening, plasmapheresis blood donors, and people having a range of blood tests for other conditions.
  This suggested the proportion of Australians with antibodies against SARS-CoV-2 ranged from 0.15% to 0.79% after the first wave of the pandemic. The lowest seroprevalence was seen among people of all ages having a general pathology blood test and the highest being among women aged 20-39 years undergoing antenatal screening.
  The authors calculated that even with a seroprevalence of 0.15%, this would have represented 1 in 670 people infected with SARS-CoV-2, or 3.5-times higher than the actual notified cases to the end of April. However the finding was contrasted with seroprevalence studies elsewhere in the world, which have found seroprevalence as high as 10% in countries such as the United States.
  Most of the samples that tested positive for SARS-CoV-2 antibodies showed low concentrations of antibodies, which the authors said suggested the infections were mild or asymptomatic. Around 60% of the seropositive individuals had neutralising antibodies to SARS-CoV-2, which is lower than levels reported in other studies. This may relate to the populations tested: hospitalised patients may have experienced more severe disease and generated higher levels of antibodies, whereas the samples in this study came from non-hospitalised individuals.
• Here are the latest confirmed COVID-19 infection numbers from around Australia to 9pm Tuesday:
  National – 27,678, with 907 deaths
  ACT – 114 (0)
  NSW – 4474 (5)
  NT – 41 (1)
  QLD – 1178 (1)
  SA – 518 (1)
  TAS – 230 (0)
  VIC – 20,345 (0)
  WA – 778 (2)