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Judging risk of transmission with COVID-19 testing – Expert Reaction

The Ministry of Health has today reported 25 new cases of COVID-19 in New Zealand, with a potential mix of new and historic infections.

The MoH has recently cited international research, which says historic infections are not infectious. However, those with new infections pose a risk of community transmission. Different types of testing can help to determine whether an infection is old or new.

Earlier this month, the SMC asked experts to comment on the latest developments in COVID-19 testing. Today, we asked for comment on the use of COVID-19 testing to determine the relative risk of a positive case.  

Dr Nikki Moreland, Senior Lecturer in Immunology, University of Auckland, comments:

“Serology testing enables you to look back in time and see who has previously had an infection. That’s because there is a time delay of approximately two weeks between someone being infected with virus and then developing detectable levels of antibodies to the virus, and serological testing is measuring those antibodies. This means serological testing allows cases that were infected weeks or even months ago to be identified, while standard swab tests generally only identify those that are currently infected.”

No conflict of interest.