Imperial Covid study finds infection rate rises 3-6 months after vaccine dose

Prevalence of 'breakthrough infections' rises again boosting case for boosters

Margaret Keenan, the first person to receive the coronavirus vaccine in December last year, receives her booster jab at University Hospital Coventry. Getty Images

People most at risk from Covid-19 are being urged to have a booster vaccine after researchers discovered evidence of more “breakthrough infections” for those fully inoculated more than three months previously.

Experts on the Imperial College London-led React-1 study monitored home swab tests taken by more than 100,000 people in England between September 9 and 27 – 764 were positive for the virus.

Among those fully vaccinated, the prevalence of infection (0.55 per cent) was higher for those who had their second dose of vaccine three to six months ago, compared with those who had who received their second shot less than three months ago (0.35 per cent).

"We found more breakthrough [Covid-19] infections among those who received their second vaccine dose between three and six months ago than those whose second dose was less than three months ago,” said Christl Donnelly, professor of statistical epidemiology at Imperial.

“However, booster doses offer the prospect of increased protection, lowering population infection levels.”

The government is offering booster shots for those most at risk from Covid-19 who were given their last dose at least six months ago.

Health Secretary Sajid Javid said it was important that “those eligible to get their booster vaccine to prolong their existing protection. I urge anyone who needs one to get a jab as soon as possible – it’s vital to keep you and your family safe this winter.”

The study also found that cases were highest in school-aged children – one in 43 five to 12-year-olds, and one in 39 13 to 17-year-olds.

“Our latest data show that infections are high and rising in school-aged children. Households with children also had a higher prevalence of infection, suggesting that children may be passing on the virus to those they live with,” said Prof Paul Elliott, director of the React-1 programme.

“These trends reinforce how important it is for children aged 12 and above to get vaccinated and help curb the spread of infection, and minimise disruption to education.”

Mr Javid said the findings showed "how important it is for young people to get the jab".

Infections were more than twice as high in those unvaccinated compared with those who received two doses. Vaccine effectiveness against infection was 44.8 per cent for AstraZeneca and 71.3 per cent for Pfizer/BioNTech.

“As we move towards winter, it is as important as ever that we continue to act responsibly in order to avoid transmission,” said Dr Jenny Harries, chief executive of the UK Health Security Agency

“While cases remain high, the vaccination programme is ensuring that this does not translate to a similarly high number of hospitalisations and deaths.

"We are urging everyone who is eligible to come forward for vaccination. It is the best way to reduce transmission and protect ourselves and those we love.”