8 July 2020
The Government has formally confirmed that it will not use any of the current or future serology tests to assess how widespread the Covid19 disease has been in New Zealand.
In answer to an Official Information Request by the Covid Plan B group, the Director of the COVID-19 Health System Response team in the Ministry of Health said serology tests would underestimate the true level of exposure to Covid-19.
Epidemiologist Simon Thornley says the new policy is the opposite of what was done in 2009 when serology data on low prevalence of swine flu convinced health officials not to take extreme control measures.
“Serology testing will underestimate the true prevalence, but that will be many times more accurate than just guessing from tests of people presenting with symptoms.
“Fear and uncertainty are driven by lack of information. The more we know, the better we can fight disease. It has been the policy in the past, so it’s strange not to do it now.”
Thornley says a consistent picture is emerging that nose tests for Covid-19 are only picking up a small fraction of all cases.
“Antibodies, present in the blood as well as T cell immune responses to the virus are revealing the coronavirus has reached far more people than listed in the daily “cases” statistic.
“That is important because it would reveal the true effectiveness of our protective measures, and the true state of our population immunity to coronavirus.”
In response to the OIA request for data from serology testing, the Government confirmed:
“Currently there are no Ministry sanctioned seroprevalence studies being performed”.
It claimed that this was supported by a letter in the Nature Medicine journal which indicated that one study found variability in individuals; 40% of asymptomatic people became seronegative and 13% of symptomatic people became negative for IgG [An immunoglobulin] as they recovered.
It noted that a study had been undertaken by the Southern DHB, and that “Positive COVID-19 cases from the Southern DHB study will be confirmed on a second assay to increase positive prediction value.” It said “future studies will have to learn from the Southern DHB study and adapt its methodology accordingly.” The Ministry added that there had been blood mononuclear cell collection by the University of Otago which would be used to perform future mediated response testing.
Contact Simon Thornley 021 299 1752