Shares of Wetherby-based diagnostics company Avacta Group plc fell about 30% on Monday after it announced it has paused sales of its Covid-19 AffiDX antigen lateral flow test (LFT) to replace antibodies in the device and improve its ability to detect the Omicron variant.

Avacta said laboratory analysis indicates “that the sensitivity of the test is reduced at lower viral loads when compared with the sensitivity of the AffiDX test with previous SARS-CoV-2 variants.”

Avacta said it took the decision independently “whilst it replaces the antibody in the product to ensure that its performance with the Omicron variant matches the high performance with previous mutations.”

In a stock exchange statement, the Wetherby firm said: “Avacta Group plc … provides an update on the performance of the AffiDX SARS-CoV-2 antigen lateral flow test (LFT) with the Omicron variant.

“The performance of all rapid antigen tests has come under recent scrutiny in light of the large number of mutations in the Omicron variant of the SARS-CoV-2 virus and the US Food and Drug Administration, as well as other sources, has indicated that antigen tests generally will detect the Omicron variant but may have reduced sensitivity.

“As reported on 15 December 2021, the AffiDX SARS-CoV-2 antigen test has been shown to detect the Omicron variant of the SARS-CoV-2 virus in patient samples in a small clinical study.

“Whilst the AffiDX antigen test is effective at identifying high viral loads of Omicron, further laboratory analysis carried out by Avacta indicates that the sensitivity of the test is reduced at lower viral loads when compared with the sensitivity of the AffiDX test with previous SARS-CoV-2 variants.

“The AffiDX SARS CoV-2 antigen lateral flow test contains both a proprietary Affimer reagent and a commercially available antibody.

“Our data show that the Affimer reagent in the AffiDX test detects the Omicron variant with the same sensitivity as the Delta variant, and it is the performance of the antibody, with which the Affimer is paired in the test, that has been affected by the additional Omicron mutations.

“The company has therefore independently taken the decision to pause sales of the AffiDX antigen test whilst it replaces the antibody in the product to ensure that its performance with the Omicron variant matches the high performance with previous mutations.”

Avacta Group CEO Alastair Smith said: “The continued high performance of the Affimer reagent in the AffiDX antigen test, despite the large number of mutations in the Omicron variant, is testament to the robustness of our platform technology.

“As a responsible business, we set very high standards for ourselves and our products and have continually kept the performance of the AffiDX antigen test under review as new SARS-CoV-2 variants have arisen.

“Our determination to only provide high quality, high performance diagnostic tests has led us to the correct decision to pause all marketing of the AffiDX lateral flow antigen test.

“We have, of course, been unable to market the product in the UK since October 2021, as the product continues to await approval under the new CTDA regulatory process.

“We believe COVID-19 testing remains a long-term commercial opportunity.

“We will therefore use the robustness of the Affimer platform, and what we have learned about the SARS-CoV-2 virus, to generate the next generation antigen test that will be as resilient as possible to any future mutations.

“The performance of other marketed SARS-CoV-2 antigen lateral flow tests may well be adversely affected by the Omicron variant.

“This mutant is already the dominant SARS-CoV-2 variant in many countries and may soon be the dominant variant globally.

“We therefore believe it is essential that similar Omicron sensitivity studies be performed on all SARS-CoV-2 antigen tests and the results communicated to ensure the public can have confidence in the results these tests generate.”