The proportion of people dying of coronavirus who do not have underlying conditions has risen in recent weeks, from below 1% to about 5% of the total, Guardian analysis has found.

The analysis, based on daily statements released by NHS England from 5 March onwards, found that the proportion of people dying with no underlying conditions had increased sharply in the last three weeks.

Experts said the data did not suggest that the proportion of deaths in otherwise healthy individuals would continue to increase, because those already in poor health were likely to have succumbed to the disease earlier.

Prof Babak Javid, principle investigator at Tsinghua University School of Medicine in Beijing and consultant in infectious diseases at Cambridge University Hospitals, said the larger proportion of previously healthy people becoming infected explained the difference. “Mortality always lags, so as the pandemic was spreading, a larger proportion of the population was getting infected,” he said. “So low probability events, for example, people who are otherwise healthy dying of Covid-19, become more statistically probable.”

Eleanor Riley, a professor of immunology and infectious disease at the University of Edinburgh, said the data had become more reliable as the number of deaths had increased. “It does seem that the rate is settling at 5%-6% and I expect it will probably stay at about that rate,” she said.

Jason Oke, a statistician with the Nuffield Department of Primary Care Health Sciences, University of Oxford, said the increase in the number of deaths in people without underlying conditions observed in the early phase of the outbreak needed to be treated with caution and did not necessarily mean the number of deaths among otherwise healthy people would continue to rise.

Thomas House, a reader in mathematical statistics at University of Manchester, said it was important to remember that an underlying condition not being recorded at the time of death did not necessarily mean that the individual did not have an underlying health problem, for example where someone had not previously been diagnosed with a chronic condition.

On Thursday the Office for National Statistics released figures on coronavirus deaths in England and Wales in March, including deaths occurring outside hospitals. It found that 91% occurred among people with one or more pre-existing conditions.