LONDON (Reuters) – An increase in the number of deaths in England and Wales in recent months that have not been linked to COVID-19 could indicate that undiagnosed cases are killing more people than previously thought, data from the Office for National Statistics showed on Friday.

The United Kingdom has the second highest COVID-19 death toll in the world after the United States, with over 50,000 people dying from confirmed or suspected cases of the disease, according to a Reuters tally of official data sources.

ONS figures showed that there were 46,380 excess deaths, the number of deaths above the expected, between March 7 and May 1, and that just over a quarter of those – 12,900 – did not officially involve the coronavirus.

But in an analysis, the ONS said that undiagnosed cases of the disease could explain excess deaths, especially among the older population.

“Undiagnosed COVID-19 is a likely explanation for some of non-COVID-19 excess deaths observed in this setting, because of the increased vulnerability of this population,” the ONS said.

People in retirement and nursing homes have been particularly vulnerable to the illness, and Prime Minister Boris Johnson’s government has been criticised for failing to protect this sector adequately.

Richard Murray, Chief Executive of the King’s Fund health charity, said the figures showed that social care, or care outside hospital settings, should be taken as seriously as the National Health Service.

“This analysis confirms that the true death toll for COVID-19 is significantly higher than the numbers reported so far, with the majority of excess deaths likely linked to undiagnosed COVID-19,” he said in a statement.

Separately, study into the prevalence of the disease in England showed further evidence of declining infection rates in the country.

These ONS figures showed that at any given point between May 17 and May 30, an estimated average of 0.10% of the community population had COVID-19, or around 53,000 people.

That compares to 136,000 people who were estimated to be infected earlier in May.

Friday’s estimate was based on tests on 19,723 people in 9,094 households.