The creation of new nursing assistant posts should be scrapped and money invested in “real nurses”, experts say after research suggested the use of lower skilled posts was a risk.
Rollout of the new nursing associate roles starts in England in December.
Research in the BMJ Quality and Safety journal linked the use of junior care roles to higher death rates.
But ministers rejected the criticism, saying the new posts were on top of investment in fully qualified nurses.
The new associate roles are seen as bridging the gap between nurses and healthcare assistants.
They will undergo two years of training and be involved in the clinical aspects of care, including medication administration.
But the team of academics, drawn from the US and Europe, questioned the wisdom of the move.
Their research used surveys of nurses and patients, staffing data and death rates.
It did not look specifically at nursing associate roles – as these were not being used in the countries studied.
But they were able to monitor the impact of using staff that assist nurses, such as the healthcare assistant role routinely used in the NHS.
The average death rate was 12.8 per 1,000 patients discharged.
A 10% increase in the ratio of fully qualified nurses was linked to an 11% fall in the chances of a patient dying.
Patient satisfaction was also higher.
Prof Peter Griffiths, of Southampton University, said: “England has one of the lowest percentages among European countries of professional nurses at the bedside already.
“Our study suggests that the NHS needs to focus on achieving safe registered nurse staffing levels as a means to achieve better outcomes including improving patients’ satisfaction with their care.”
The Department of Health questioned whether the way the research was carried out could give an accurate prediction of the impact of the new nursing associate roles.
A spokesman added: “Our plans complement not replace existing fully qualified registered nurses.
“This will ensure that nurses can make the best use of their time in providing outstanding patient care.”