One in four people in their mid-30s to mid-50s are no longer following the full rules around self-isolation after a positive Covid test, according to a survey that suggests compliance with the requirements has slipped since the summer.

The latest figures from the Office for National Statistics, based on a survey of 881 people in England in late September and early October, show that only 75% of respondents aged 35 to 54 complied with the full rules around self-isolation for the 10 days after testing positive for coronavirus.

The number is down substantially from the 86% compliance reported by the ONS in July, and suggests that those in their mid-30s to mid-50s are now the least able, or least likely, of any age group to abide by the full requirements of self-isolation after a positive result.

Hints of lower compliance were also seen in older people, with adherence to self-isolation falling marginally in those aged 55 and over from 81% in the summer to 78% in recent weeks, according to the ONS survey.

Evidence for an opposing trend was seen in younger people, with 82% of 18- to 34-year-olds reporting full compliance with self-isolation rules in the latest survey, up from 75% in the summer.

The findings came as further ONS data gathered between January and September 2021 showed that unvaccinated people were 32 times more likely to die from Covid than fully vaccinated individuals.

The latest round of the ONS self-isolation survey collected responses from adults in England between 27 September and 2 October. The ONS said the statistics were “experimental” and based on a small number of respondents who reported their own behaviour, so should be treated with caution.

Overall, the ONS estimates that 78% of individuals who have a positive Covid test follow the full requirements for self-isolation, a similar rate to the 79% seen in the previous round of the survey in July. However, the ONS said the compliance rate was “significantly lower” than levels seen earlier in the year, such as 84% in April and 86% in May.

About one-third (34%) of those who tested positive for Covid reported that isolating had a negative effect on their mental health, down from 42% in July.

“Today’s results highlight the majority of those testing positive for Covid-19 adhere to self-isolation requirements, though there has been a decrease since April and May earlier this year,” said Tim Gibbs, head of the ONS public services analysis team.

“As we continue into the winter months, it is important we monitor general adherence to self-isolation requirements, which wouldn’t be possible without our respondents,” he added.