Fully vaccinated adults can harbour virus levels as high as unvaccinated people if infected with the Delta variant, according to a sweeping analysis of UK data, which supports the idea that hitting the threshold for herd immunity is unlikely.
There is abundant evidence that Covid vaccines in the UK continue to offer significant protection against hospitalisations and death. But this new analysis shows that although being fully vaccinated means the risk of getting infected is lower, once infected by Delta a person can carry similar virus levels as unvaccinated people.
The implications of this on transmission remain unclear, the researchers have cautioned. “We don’t yet know how much transmission can happen from people who get Covid-19 after being vaccinated – for example, they may have high levels of virus for shorter periods of time,” said Sarah Walker, a professor of medical statistics and epidemiology at the University of Oxford.
“But the fact that they can have high levels of virus suggests that people who aren’t yet vaccinated may not be as protected from the Delta variant as we hoped.”
Positive tests, hospitalisations and deaths linked to Covid have been rising slowly in the UK recently. In the week to 18 August, 211,238 people had a confirmed positive test result, an increase of 7.6% compared with the previous seven days. Over the same period, there have been 655 deaths within 28 days of a positive test, a rise of 7.9% versus the previous seven days. Hospitalisations have also risen slightly, with 5,623 going into hospital with coronavirus between 8 August 2021 and 14 August 2021, a rise of 4.3% compared with the previous seven days.
The study, which is yet to be peer-reviewed, found vaccine performance has waned against Delta versus the previously dominant Alpha variant.
The analysis did not directly investigate whether the lower level of vaccine protection against Delta affected jabs’ ability to prevent severe disease. However, Dr Penny Ward, a visiting professor in pharmaceutical medicine at King’s College London, noted: “The low incidence of hospitalisation seen to date suggests that in this respect at least the vaccines are protecting individuals from developing severe Covid.”
The study – conducted by Oxford researchers in partnership with the Office for National Statistics and the Department of Health and Social Care – compared the results of about 2.6m nose and throat swabs taken from more than 384,500 adults between December 2020 and mid-May 2021, and more than 811,600 test results from 358,983 adults between mid-May and 1 August 2021 (the period of Delta’s domination).
The UK findings on peak virus levels after Delta infections in vaccinated people echoed data from a small study cited by the US Centers for Disease Control and Prevention (CDC) last month. The agency indicated those findings had underpinned its decision to recommend that people wear masks in some indoor settings, regardless of their vaccination status, especially in areas of “substantial or high” virus transmission.

News
Repurposed drugs could calm the immune system’s response to nanomedicine
An international study led by researchers at the University of Colorado Anschutz Medical Campus has identified a promising strategy to enhance the safety of nanomedicines, advanced therapies often used in cancer and vaccine treatments, [...]
Nano-Enhanced Hydrogel Strategies for Cartilage Repair
A recent article in Engineering describes the development of a protein-based nanocomposite hydrogel designed to deliver two therapeutic agents—dexamethasone (Dex) and kartogenin (KGN)—to support cartilage repair. The hydrogel is engineered to modulate immune responses and promote [...]
New Cancer Drug Blocks Tumors Without Debilitating Side Effects
A new drug targets RAS-PI3Kα pathways without harmful side effects. It was developed using high-performance computing and AI. A new cancer drug candidate, developed through a collaboration between Lawrence Livermore National Laboratory (LLNL), BridgeBio Oncology [...]
Scientists Are Pretty Close to Replicating the First Thing That Ever Lived
For 400 million years, a leading hypothesis claims, Earth was an “RNA World,” meaning that life must’ve first replicated from RNA before the arrival of proteins and DNA. Unfortunately, scientists have failed to find [...]
Why ‘Peniaphobia’ Is Exploding Among Young People (And Why We Should Be Concerned)
An insidious illness is taking hold among a growing proportion of young people. Little known to the general public, peniaphobia—the fear of becoming poor—is gaining ground among teens and young adults. Discover the causes [...]
Team finds flawed data in recent study relevant to coronavirus antiviral development
The COVID pandemic illustrated how urgently we need antiviral medications capable of treating coronavirus infections. To aid this effort, researchers quickly homed in on part of SARS-CoV-2's molecular structure known as the NiRAN domain—an [...]
Drug-Coated Neural Implants Reduce Immune Rejection
Summary: A new study shows that coating neural prosthetic implants with the anti-inflammatory drug dexamethasone helps reduce the body’s immune response and scar tissue formation. This strategy enhances the long-term performance and stability of electrodes [...]
Scientists discover cancer-fighting bacteria that ‘soak up’ forever chemicals in the body
A family of healthy bacteria may help 'soak up' toxic forever chemicals in the body, warding off their cancerous effects. Forever chemicals, also known as PFAS (per- and polyfluoroalkyl substances), are toxic chemicals that [...]
Johns Hopkins Researchers Uncover a New Way To Kill Cancer Cells
A new study reveals that blocking ribosomal RNA production rewires cancer cell behavior and could help treat genetically unstable tumors. Researchers at the Johns Hopkins Kimmel Cancer Center and the Department of Radiation Oncology and Molecular [...]
AI matches doctors in mapping lung tumors for radiation therapy
In radiation therapy, precision can save lives. Oncologists must carefully map the size and location of a tumor before delivering high-dose radiation to destroy cancer cells while sparing healthy tissue. But this process, called [...]
Scientists Finally “See” Key Protein That Controls Inflammation
Researchers used advanced microscopy to uncover important protein structures. For the first time, two important protein structures in the human body are being visualized, thanks in part to cutting-edge technology at the University of [...]
AI tool detects 9 types of dementia from a single brain scan
Mayo Clinic researchers have developed a new artificial intelligence (AI) tool that helps clinicians identify brain activity patterns linked to nine types of dementia, including Alzheimer's disease, using a single, widely available scan—a transformative [...]
Is plastic packaging putting more than just food on your plate?
New research reveals that common food packaging and utensils can shed microscopic plastics into our food, prompting urgent calls for stricter testing and updated regulations to protect public health. Beyond microplastics: The analysis intentionally [...]
Aging Spreads Through the Bloodstream
Summary: New research reveals that aging isn’t just a local cellular process—it can spread throughout the body via the bloodstream. A redox-sensitive protein called ReHMGB1, secreted by senescent cells, was found to trigger aging features [...]
AI and nanomedicine find rare biomarkers for prostrate cancer and atherosclerosis
Imagine a stadium packed with 75,000 fans, all wearing green and white jerseys—except one person in a solid green shirt. Finding that person would be tough. That's how hard it is for scientists to [...]
Are Pesticides Breeding the Next Pandemic? Experts Warn of Fungal Superbugs
Fungicides used in agriculture have been linked to an increase in resistance to antifungal drugs in both humans and animals. Fungal infections are on the rise, and two UC Davis infectious disease experts, Dr. George Thompson [...]