London, Dec 23 (IANS): Children aged 5 to 11 are three times more at risk of Covid infections as compared to the general population of England, according to a new study.

The study, by Imperial College London, showed that an estimated 4.47 per cent of primary school-aged children had the virus within the period of the study in contrast with 1.41 per cent across the country overall, The Guardian reported.

The researchers, together with market research company Ipsos Mori, analysed data from 97,000 volunteers in England to examine national Covid-19 levels between November 23 and December 14.

The results showed that infections decreased by 40 per cent or more in 12-17-year-olds and those aged 65 and above, reflecting the impact of the vaccination programme. At the same time, the cases increased in adults aged 18-54, and have remained relatively stable in primary school-aged children.

The study showed that the prevalence in children aged 12 to 17 years more than halved from 5.35 per cent to 2.31 per cent. As of December 14, 76.6 per cent children at ages 12 to 17 years had received at least one vaccine dose.

"We estimated that vaccine effectiveness against infection was 57.9 per cent in this age group," wrote Prof Paul Elliott, from the college's School of Public Health, in the paper.

In addition, the prevalence of swab positivity in adults aged 65 years and over fell by over 40 per cent from 0.84 per cent to 0.48 per cent and for those aged 75 years and over it fell by two-thirds from 0.63 per cent to 0.21 per cent.

At these ages a high proportion of participants (more than 90 per cent) had received a third vaccine dose.

"We estimated that adults having received a third vaccine dose had a three- to four-fold lower risk of testing positive compared to those who had received two doses," Eliot said.

"A large fall in swab positivity from among 12 to 17 year olds, most of whom have been vaccinated, contrasts with the continuing high prevalence among 5 to 11 year olds who have largely not been vaccinated," he noted.

The study also showed large falls in swab positivity among people aged 65 years and over, the vast majority of whom have had a third (booster) vaccine dose, reinforcing the importance of the vaccine and booster campaign.

The findings also projected that the rapidly spreading Omicron variant will become the dominant strain across the country more than three times faster than Delta overtook Alpha.

However, the speed of the vaccine rollout to secondary school-aged children and the booster rollout among adults may have helped to curb infection rates among other age groups, researchers said.