Why are Covid infections rising when 85 per cent of Scots have antibodies?
CORONAVIRUS rates in Scotland have continued to soar despite more than eight in 10 people having Covid antibodies, according to the latest surveillance. The Office for National Statistics research also shows that the gap between Scotland and England has narrowed, with 84.7 per cent of people in Scotland estimated to have Covid antibodies by the week ending June 20 compared to 89.8% in England. Previously there was a gap of around 10%, which First Minister Nicola Sturgeon said had been a factor in explaining why Scotland's Covid rates had overtaken the rest of the UK with Tayside's ranked the worst in Europe by the World Health Organisation. The ONS antibody surveillance study is based on gathering blood samples from thousands people living in the community and testing them for antibodies. This data is then used to extrapolate an estimate for the overall prevalence of antibodies across the population as a whole. READ MORE: Why the Delta variant has left herd immunity through vaccination mathematically impossible  Antibodies can be present in the blood both as a result of vaccination or from a prior Covid infection, but this does not necessarily mean a person is immune. There is some evidence from India that people previously infected with Covid caused by non-Delta strains of the virus were re-infected once the Delta variant began to spread there. Coupled with low vaccination rates, it is thought that this may explain why the population's high exposure earlier in the pandemic did not cushion India from a dramatic second wave. In addition, people who have had only a single vaccine dose can test positive for antibodies, but still remain at comparatively high risk of infection. According to estimates from Edinburgh University's EAVE II project - which is tracking the vaccination rollout - a single shot of either the AstraZeneca or Pfizer vaccines will reduce the risk of symptomatic infection from the Delta strain by only 33% 28 days or more after vaccination. Even two weeks after a second dose, protection is 83% (Pfizer) and 61% (AstraZeneca). To date, 63% of adults in Scotland have been fully vaccinated. Concerns have also been raised that the emergence of new, more transmissible variants has "moved the goalposts" in terms of achieving herd immunity. READ MORE: Jason Leitch explains why Scotland now tops the list for Covid rates in Europe  Professor Devi Sridhar, chair of global public health at Edinburgh University and an advisor to the Scottish Government on Covid-19, told the BBC: "Because of the variants being more transmissible, the percentage of the population that you have to vaccinate - your herd immunity threshold - moves higher." The calculation for the herd immunity threshold is based on an equation which takes into account the R number of a virus in the absence of any mitigations, and the vaccine efficacy against infection. For the original Wuhan strain, it was estimated that roughly 75% of the total population would have had to be fully vaccinated for herd immunity to be reached. With the Alpha (Kent) strain - estimated to be 50% more transmissible - coverage would have had to reach around 90%, but the Delta variant pushes herd immunity through vaccination effectively out of reach. Even if the UK was only using the Pfizer vaccine, 100% of the total population - not just adults - would have to be fully vaccinated to achieve herd immunity through vaccination alone. READ MORE: Fears soaring case numbers could hamper overseas travel return  However, since two thirds of people are receiving AstraZeneca - which is highly protective against Covid deaths and hospitalisations, but weaker than Pfizer against infections - the herd immunity equation becomes mathematically impossible. The Joint Committee on Infection and Vaccination (JCVI) is currently considering whether to rollout vaccinations to children aged 12-17, which would help to bring the population closer to herd immunity but this is complicated by ethical considerations due to their own risk from the disease being extremely low. There are still hopes that the virus can be brought down to low, endemic levels, however, once enough people are vaccinated and as long as the virus R number is kept under control in the meantime through mitigations such as physical distancing, facemasks to limit transmission, ventilating indoor spaces and meeting outdoors where possible.