COVID-19 vaccination cuts infection risk by half in school-aged children - REACT

New data from the REACT study show that infections have been falling but are still very high, and are now at a similar rate to January this year.

Results from swab tests taken at home by over 100,000 people in England between 19 October and 5 November showed that 1.57% of people were infected, or 1 in 64. This is slightly lower than the study’s recent interim data, when 1.72% were infected as of 29th October, but almost twice as high as data from September.

School-aged children had the highest infection prevalence at 5.21% for 13-17-year-olds, and 4.95% for those aged 5-12, or around 1 in 20. However the study, led by Imperial College London with Ipsos MORI, also found that vaccination was helping to reduce virus spread among children. Those aged 12-17 who had received a single Pfizer/BioNTech dose had around a 56% lower risk of infection compared to unvaccinated children. The risk was even lower for symptomatic infection, at around 68%.

"It is possible that the prevalence rate could rise once again now that children have returned to school following half-term." Prof Paul Elliott School of Public Health, Imperial

The study also looked at the effectiveness of booster doses at preventing infection, finding that the risk of infection was around three times lower in those who had received a third dose, compared to those who had received two. For those who were aged 50 and above, having a third dose reduced the infection risk by around half compared to two doses.

Professor Paul Elliott, director of the REACT programme from Imperial’s School of Public Health, said: “Although hospitalisations and deaths remain lower than previous peaks, the data show that infections across the country remain very high. The rate of prevalence has steadily declined throughout this round, but an overall figure of 1.57 per cent is still nearly two-fold higher than that recorded in the previous round.

“It is possible that the prevalence rate could rise once again now that children have returned to school following half-term, though this could be at least partially offset by as many people as possible having booster jabs when offered and those aged twelve years or over having the vaccine.”

These findings from the ongoing REal-time Assessment of Community Transmission (REACT-1) programme, commissioned by the Department of Health and Social Care, are available here in a pre-print report and will be submitted for peer-review. Data are continually reported to the Government to inform decision-making.

Monitoring variants

For this latest round of the REACT study, 100,112 people swabbed themselves at home and their samples were analysed by PCR testing. 1,399 of these were positive, giving an overall weighted prevalence of 1.57%. Weighting is where the researchers make adjustments to their calculations to ensure the sample reflects England’s population.

"As we approach winter, it is vital that everyone eligible comes forward for their jabs – whether that’s their first dose, second or a booster." Dr Jenny Harries CEO, UK Health Security Agency

Of the positive samples, 841 were further analysed to read the viral genetic code, all of which were the Delta variant. Almost 12% were the AY.4.2 sub-lineage, defined as a variant under investigation, meaning it is being monitored. People who were infected with AY.4.2 were less likely to have any symptoms less likely to have the ‘classic’ symptoms (loss or change of sense of taste or smell, fever, new persistent cough).

Looking at trends across this study period, infections fell from a very high level during October with an R number of 0.76. However there was wide variation in the data at the end of the testing period, meaning it’s not clear whether infections were continuing on a downward trend.

Dr Jenny Harries, Chief Executive of the UK Health Security Agency, said: “This round of REACT provides another reminder of the effectiveness of the vaccines against COVID-19. As we approach winter, it is vital that everyone eligible comes forward for their jabs – whether that’s their first dose, second or a booster.

“Remember that anyone over 12 years old is now able to receive their first jab, and boosters will soon be offered to everyone over 40. Please do take up that offer to ensure your immunity does not wane.”

Coronavirus infection trends

Across the country, the highest number of infections were found in the South West at 1.97%, which is more than three times higher than the previous testing round in September. Infections rose in almost all areas of the country except the East Midlands and Yorkshire and the Humber.

Other key findings include:

• Infections were more than three times higher in households with children compared to those without (2.62% vs 0.74%).
• The rate of breakthrough infections in people who have had two vaccine doses has doubled since July, possibly in part due to waning of immunity.
• Death rates have remained lower than might have been predicted on the basis of infection prevalences since widespread vaccination.
• Prevalence doubled in those aged 65 and above compared to September, almost all of whom were vaccinated.

Due to the very low number of adult participants in this round who were unvaccinated, the researchers do not estimate the effectiveness of vaccination against infection for adults. This is because the calculation requires a comparison of vaccinated and unvaccinated groups, and there were too few unvaccinated adults to make a fair comparison.

"Our latest data also reinforce the need for and importance of booster vaccinations in preventing immunity from waning, and so I would encourage all people to take up their offer. " Prof Christl Donnelly Professor of Statistical Epidemiology

Professor Christl Donnelly, Professor of Statistical Epidemiology at Imperial and Professor of Applied Statistics at the University of Oxford, said: “The data on infection rates among vaccinated and unvaccinated adults need to be interpreted with caution as there are many compounding factors at play, particularly the low numbers of unvaccinated individuals and social and demographic factors such as age.

"But what we can see very clearly is that since the rollout of COVID-19 vaccination, death rates have remained low relative to infection prevalence, demonstrating their effectiveness at preventing infections from causing people to become seriously ill and die.

“Our latest data also reinforce the importance of booster vaccinations in preventing immunity from waning, and so I would encourage all people to take up their offer. I will be doing so later this month.”

CEO, Ipsos MORI – Kelly Beaver said: “The high prevalence found in this round of REACT reminds us all of the importance of remaining vigilant, while the data on booster jabs is an important reminder to everyone to get their booster jab when it’s made available to them to ensure the best protection against COVID-19.”