According to a comprehensive analysis of UK data, fully vaccinated adults could have virus levels that are as high as those who were not vaccinated if they become infected by the Delta variant. This supports the notion that it is very unlikely that an individual will reach the threshold for herd immunity.
The evidence is overwhelming that Covid vaccines provide significant protection against death and hospitalisations in the UK. This new analysis shows that even though being fully vaccinated reduces the chance of contracting Delta, a person can still be infected with similar levels to those who are not.
Researchers caution that the implications of this for transmission are still unclear. Researchers are still not sure how much transmission can occur from people who have received Covid-19 vaccines. For example, some may be exposed for shorter periods of times. Sarah Walker, a professor of epidemiology and medical statistics at the University of Oxford, stated that we don't know how many cases of Covid-19 infection could result.
However, they can be susceptible to high levels of virus. This suggests that those who have not yet been vaccinated may not as well be protected against the Delta variant.
Recent trends in the UK have seen a slow rise in positive tests, hospitalisations, and deaths due to Covid. The number of confirmed positive tests for Covid in the week ending 18 August was 211,238. This is 7.6% more than the seven previous days. There have been 655 deaths in the 28 days following a positive test result, an increase of 7.9% over the previous seven days. Hospitalisations have increased slightly as 5,623 people with coronavirus were admitted to hospital between 8 and 14 August 2021. This is a 4.3% increase compared to the previous seven days.
The vaccine performance against Delta was lower than the Alpha variant, according to the study that is still being peer-reviewed.
Although the analysis did not examine whether lower levels of vaccine protection against Delta affected jabs' ability to prevent severe diseases, it did explore this possibility. Dr Penny Ward, a visiting professor of pharmaceutical medicine at Kings College London noted that the low rate of hospitalizations suggests that vaccines are at least protecting people from severe Covid.
Oxford researchers, in collaboration with the Office for National Statistics and Department of Health and Social Care, compared the results of approximately 2.6m nose and neck swabs from more than 384,000.50 adults between December 2020 and mid May 2021 and more than 811,000.600 test results from 358.983 adults between mid–May and 1 August 2021 (the period of Deltas dominance).
The UK's findings about peak virus levels in people who have been vaccinated against Delta infection echoed data from a smaller study cited last month by the US Centers for Disease Control and Prevention. These findings had influenced the agency's recommendation to wear masks indoors, regardless of vaccination status.
These data show that vaccinated people can still transmit Covid to others. Dr Koen Pouwels from Oxford University's Nuffield department for population health, stated that these datasets are a reminder of the need to test and isolate to reduce the risk of transmission. He suggested that this potential for transmission makes it even harder to achieve herd immunity.
The concept of population immunity or herd immunity is based on the fact that a large percentage of a population has been infected or has received vaccinations. This provides indirect protection against an infectious disease for those not vaccinated or who have never been infected.
Walker, who is also the chief investigator for UK analysis, stated that the hope was to be able to vaccinate enough people in order to protect the unvaccinated. Partly, I believe that the higher levels of virus in [Delta] infection in vaccinated individuals is consistent with the fact unvaccinated persons are at greater risk.
Researchers also discovered that two doses Pfizer/BioNTech vaccine have a 15% higher initial effectiveness against new infections than the Oxford/AstraZeneca jab. However, protection decreases quicker than two doses Oxford/AstraZeneca. Walker said that protection is almost the same after being fully vaccinated with either vaccine for four to five months.
Pouwels added that even though there are slight decreases in protection against infections with high viral burden and infections that are not all-infected, overall effectiveness is still high. This is because we started at such a high level.
