Nearly 1,000 nursing homes in the Netherlands have reported at least one coronavirus infection in the last four weeks, beating the previous record set in January.

The figure of 970 represents 40% of all residential care homes in the Netherlands. In general those infected suffer a milder form of the illness than a year ago, but the death rate is roughly the same.

Cees Hartogh, professor of geriatric medicine at the VU university in Amsterdam, said waning vaccine efficiency was among the likely reasons for the high number of deaths. Around 22% of nursing home residents who had been vaccinated died after contracting Covid-19.

Hartogh said the deadlier Delta variant, which first appeared last spring, was also a likely factor. ‘Not only is it more infectious than earlier variants, but it possibly has a more fatal outcome for vulnerable older people.’

He said booster vaccines, which are being given in most nursing homes from this week, should improve the situation. ‘We can help to reduce the number of infections and the transmission of the disease with an extra vaccine. And, secondly, we can reduce the risk of serious illness.’

But Hartogh warned that the lack of co-ordinated records was holding back researchers’ efforts to track the disease. Some nursing homes keep details of which residents have been vaccinated in their electronic patients’ dossiers, while others are still using paper records or their in-house medication logs.

‘We have data, but if there was a centralised registration system we would have access to far more,’ he said.