LONDON (Reuters) - Fully-vaccinated people have an around 50 to 60% reduced risk of infection from the Delta coronavirus variant, including those who are asymptomatic, a large English coronavirus prevalence study found on Wednesday.

Imperial College London researchers said people who reported receiving two vaccine doses were half as likely to test positive for COVID-19, adjusting for other factors such as age, whether or not the people tested had COVID-19 symptoms.

Focusing on those who had COVID-19 symptoms, effectiveness rose to around 59%, according to the study, which covered a period when the Delta variant completely displaced the previously dominant Alpha variant.

The researchers said this was not surprising or worrying, given that PHE estimates were based on those who have symptoms and get tested, while the Imperial study is designed to pick up more people.

The study found that the link between infections and hospitalisations, which had previously weakened, had started to reconverge, a move which coincides with the spread of Delta among younger people who may not be fully vaccinated.

The researchers said that overall, prevalence in unvaccinated people was 1.21%, three times higher than the 0.40% prevalence in fully vaccinated people, and that the viral load among people with COVID was also lower in vaccinated people.

The researchers were presenting the latest findings of Imperial's REACT-1 prevalence survey, which showed there was a fourfold increase in infections in a month to reach 1 in 160 people in England.

Fully vaccinated COVID-19 patients infected with the Delta variant experienced "significantly lower odds" of moderate or severe outcomes, according to a local study.

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