One-in-a-billion risk of mad cow disease spreading through NZ blood donation

Experts say there’s a mere one-in-a-billion risk of mad cow disease spreading through blood transfusions in New Zealand – yet it continues to exclude thousands of potential donors here amid repeated shortages.

Their analysis has prompted a fresh call for New Zealand to follow other countries and ease restrictions put in place more than two decades ago – a change the New Zealand Blood Service itself has asked regulators to consider.

In the year 2000, one in 10 people here were barred from giving blood as they lived in the UK for six months or more during the mad cow disease epidemic over the 1980s and 1990s.

Because the disease – formally Variant Creutzfeldt-Jakob disease, or vCJD – could lay dormant within a person for decades before they developed the fatal illness, that policy has stayed in place.

Yet the risk has been extremely low – and so small, in fact, that two health experts have quantified it at about one in a billion each year.

“We can’t say the risk is zero, because of uncertainty around the incubation period that comes with these infections – but there hasn’t been a case for four years now,” said Professor David Hayman, an infectious diseases expert at Massey University.

In an editorial published in today’s New Zealand Medical Journal, Hayman and Otago University epidemiologist Professor Michael Baker also noted that, of 232 cases ever recorded globally, just three had been definitively linked to blood transfusions.

Using UK case numbers, population estimates and transfusion data, they calculated that the risk would to New Zealand would be approximately 0.005 cases annually – an estimate aligning with similar risk assessments made for Australia.

Australia, along with other countries like Ireland, has already relaxed its restrictions.

With a dire need for blood products and the tiny probability of transmission, Hayman and Baker suggested it was time for New Zealand to consider doing the same, while maintaining a focus on public health safety.

Hayman said a policy change could make thousands more people suddenly eligible to give blood here.

“At the minute, when blood is an urgent or semi-urgent product, what are harm are we doing by keeping people these from donating, compared with a potential risk that we think is extraordinarily low?” he said.

“Even if this resulted in a 5 per cent increase in donors, that could help reduce some of the bottlenecks.”

Having already carried out its own assessment, the New Zealand Blood Service (NZBS) recently lodged a submission with regulator MedSafe to lift the deferral.

“Any changes to the donor eligibility criteria in New Zealand can only be made once we have approval from Medsafe,” NZBS spokeswoman Asuka Burge said.

While the service hoped to see changes made this year, it pointed out the process – involving months for MedSafe to complete its assessment, along with the service having to update its internal systems – could take some time.

MedSafe has been approached for comment.

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.