Two more antigen tests get US nod


A Covid-19 diagnosis first this week has come as a result of different approaches and technologies converging. Quidel has gained US FDA authorisation for the first test for both the coronavirus and flu that works by detecting viral antigens rather than RNA. Nicknamed the ABC test because it tests for influenza A and B as well as Covid-19, the Sofia 2 Flu + Sars Antigen assay detects the nucleocapsid protein from the three viruses in a single nasal swab. It may be used at the point of care, returning results inside 15 minutes, and Quidel claims impressive accuracy, as shown below. With Covid-19 cases on the rise in many countries and the flu season getting under way in the Northern hemisphere, this kind of combination test could help save money. Quidel was the first company to gain authorisation for an antigen test for Covid-19 in mid-July. Another antigen test, this time developed by New Jersey-based Access Bio, was also authorised last week. Access now has the FDA’s rubber-stamp for all three main types of Covid-19 tests, its molecular and antibody assays having been authorised in July.

Accuracy figures for Quidel's ABC test
Virus PPA vs PCR (%) NPA vs PCR (%)
Sars-CoV-2 95.2 100.0
  Sensitivity vs culture (%) Specificity vs culture (%)
Influenza A 90.0 95.0
Influenza B 89.0 96.0
Note: PPA and NPA are analogous to sensitivity and specificity, respectively. Source: company release. 

Note: "other" includes six antigen tests, three home sampling kits and two IL-6 tests.

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