Legal advice sought on mixing vaccines made by different manufacturers

Vaccine mixing could play into rollout of booster shot campaign, plans for which are being examined by the HSE

The Department of Health has sought legal advice on mixing Covid-19 vaccines made by different manufacturers, The Irish Times has learned.

Due to the impact of going “off label” and mixing vaccines in a way that was not included in clinical trials, legal input has been sought from the Attorney General’s office and other agencies before it is passed to Minister Stephen Donnelly for a final decision.

Preliminary advice on the issue, which could see different vaccines mixed in a two-dose regime, was given to chief medical officer Dr Tony Holohan in recent weeks by the National Immunisation Advisory Committee. However, a formal recommendation has yet to be given to Mr Donnelly.

Hospital Report

Total doses distributed to Ireland Total doses administered in Ireland
9,452,860 7,856,558

The Department of Health on Tuesday night said the advice would be provided to the Minister “shortly”.


Proponents of vaccine mixing argue that it could offer more potent immune system responses, and while going “off label” is frequently done in the Irish healthcare system and elsewhere, there are additional factors being considered for the Covid-19 vaccine.

As the vaccine is being given to a large group of people, most of whom are healthy, the risk profile is different compared to departing from manufacturer’s clinical trials for other medicines, which is often done for ill people. There is also extra scrutiny on the high-profile Covid-19 vaccine rollout.

Same shot

If the decision to mix vaccines within a two-dose regime was made it may ultimately only apply to a minority of people who are not already doubly vaccinated with the same shot. However, it could also play into the rollout of a booster shot campaign, plans for which are currently being examined by the Health Service Executive (HSE).

More research is expected from several trials and studies of real-life data from countries where booster shots have been given.

Dr Holohan has already advised that certain groups – including the over 80s, those in long-term care facilities and healthcare workers – be given an mRNA vaccine like Pfizer or Moderna as a booster.

The four vaccines currently being administered in Ireland have received a conditional marketing authorisation from the European Medicines Agency (EMA) as their approval was based on less comprehensive clinical data than normally required. Some countries, including Germany, have opted to mix vaccines, but there is no offical EU advice on the issue.

In the US such “off label” use is not allowed under the emergency-use authorisation granted by the Food and Drugs Administration, though full authorisation for some vaccines is expected shortly.

The State’s medicines regulator, the Health Products Regulatory Authority, pointed out that in many EU states expert committees have recommended use of heterologous (mixed) vaccination.

“The EMA and European Centre for Disease Prevention and Control have jointly stated that whilst there are good scientific grounds to expect this strategy to be safe and effective when applied to vaccination against Covid-19, that currently they are not in a position to make any definitive recommendations with regard to the licensed use of different Covid-19 vaccines for the two doses,” a spokesman told The Irish Times.

Emerging data

Preliminary results from studies in Spain, Germany and the UK have raised no safety concerns, but more data is being awaited.

“The EMA will continue to review emerging data as they become available, and the Health Products Regulatory Authority will inform the Department of Health and the National Immunisation Advisory Committee of any relevant updates,” the regulator said

A further 1,508 cases of Covid-19 were reported on Tuesday, with 206 patients with the disease being treated in hospital, 33 of whom are in intensive care.

Jack Horgan-Jones

Jack Horgan-Jones

Jack Horgan-Jones is a political reporter with The Irish Times

Paul Cullen

Paul Cullen

Paul Cullen is Health Editor of The Irish Times