‘One in a billion’ risk of ‘mad cow disease’ from NZ blood donations

The risk of “mad cow disease” being transmitted through donated blood if current restrictions were removed is about one in one billion annually, prompting researchers to suggest our donor policies to be relaxed.

At present, New Zealand excludes potential donors who lived in the United Kingdom, Ireland or France for six months or more between 1980 and 1996​, due to the potential for these people to be infected with Variant Creutzfeldt-Jakob disease (vCJD).

But there’s the possibility this could change: just this month, the New Zealand Blood Service made a submission to Medsafe recommending the ban be lifted.

vCJD is a very rare, deadly degenerative brain disorder caused by an infectious prion picked up from eating contaminated beef and beef products.

Due to potentially long incubation periods, a lack of non-invasive tests, or ways to fully remove these prions from products, countries adopted a precautionary approach “in the absence of scientific knowledge” to avoid any risk of vCJD transmission from blood transfusions.

The restriction led to 10%​ of New Zealand’s active blood donors in 2000​ being excluded.

Now, Professors David Hayman​ and Michael Baker​ have estimated the annual risk of vCJD from blood transfusion in Aotearoa, if the restriction was removed.

In a viewpoint in the New Zealand Medical Journal on Friday, they crunched UK case numbers, population estimates, and donor and recipient transfusion numbers to calculate the risk to the New Zealand public.

There have been 232​ cases of vCJD – 178​ (76%)​ in the UK – with no new cases worldwide since 2019​.

Only three​ confirmed cases have been linked to blood transfusion ever, the authors say.

Due to these low numbers, countries have begun lifting restrictions on donors with potential BSE exposure: Ireland lifted its ban in 2019​, and Australia in July 2022​.

Based on approximately 131,000​ transfusions in Aotearoa annually – and accounting for some people receiving multiple transfusions – the researchers determined this might lead to 0.005​ cases annually.

That’s one in 967 million​, “or approximately one in one billion, annually”, they write.

Hayman, a professor of infectious disease ecology at Massey University and trained veterinarian, said part of the ongoing precaution around blood transfusions has been due to the long incubation period.

The peak in human cases was 23​ years ago, in 2000​, 10 to 20 years after the outbreak in cattle.

“We can’t say for sure, but we’re not seeing any more [cases]… we haven’t seen this second wave.”

Hayman said from their findings, the risk of vCJD transmission, while not zero, seemed “extraordinarily low”.

Hayman said this needed to be viewed against the potential benefit: “We know there are blood shortages, some are acute.”

Less than 4%​​ of New Zealand’s eligible population donate blood, and the service says it needs 40,000​ new donors in the next 12 months to ensure it can remain self-reliant and meet demand.

He stated there is an ongoing need for surveillance of vCJD, but that it seemed timely to follow Australia and remove the restriction on donors potentially exposed to bovine spongiform encephalopathy (BSE) in the 1980s and 90s.

Hayman grew up in the UK, making him ineligible to give blood in New Zealand, but he said: “I would if I could.”

Asuka Burge​, the New Zealand Blood Service’s national marketing and communications manager, said any changes to donor deferral criteria must be approved by Medsafe.

This August, NZBS made a submission to Medsafe recommending the permanent deferral be lifted.

This recommendation was the result of a detailed review and risk assessment by the New Zealand Blood Services’ clinical team, alongside the most up-to-date, peer-reviewed scientific evidence, Burge said.

Submissions to Medsafe can take up to three months to be completed – potentially longer if additional information is needed.

If approval is granted, it will take about two months before the service could implement the changes.

“If and when we have a go-live date, we will communicate these changes to the public,” Burge said.

Burge said they know there will be “a lot of people genuinely quite excited about the prospect of being able to donate either for the first time or again”.

“We are really hopeful that we’ll be welcoming some new faces to our donor whānau.”