Researchers say implications for transmission remain unclear but reaching herd immunity even more challenging

Commuters on London Bridge
The research supports the idea that hitting the threshold for herd immunity is unlikely. Photograph: Guy Bell/Rex/Shutterstock
Science correspondent
Guardian (UK)

 

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.

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Biden administration to start booster shots on Sept. 20

The Biden administration is recommending booster doses for most Americans who received a coronavirus vaccine in order to combat waning immunity and the prevalence of the delta variant.

In a joint statement Wednesday, top administration health officials said people would need boosters beginning eight months after their second dose of either the Pfizer-BioNTech or Moderna vaccine.

The officials include Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky, National Institutes of Health Director Francis Collins, National Institute of Allergy and Infectious Diseases Director Anthony Fauci, Surgeon General Vivek Murthy and acting Food and Drug Administration (FDA) Commissioner Janet Woodcock.

“The available data make very clear that protection against SARS-CoV-2 infection begins to decrease over time following the initial doses of vaccination, and in association with the dominance of the Delta variant, we are starting to see evidence of reduced protection against mild and moderate disease,” the officials said in the statement.

Administration of the boosters will begin Sept. 20. At that time, the individuals who were fully vaccinated earliest in the vaccination rollout, including many health care providers, nursing home residents and other seniors, will likely be eligible for a booster, the officials said.

Booster doses will also be delivered directly to residents of long-term care facilities.

“Based on our latest assessment, the current protection against severe disease, hospitalization, and death could diminish in the months ahead, especially among those who are at higher risk or were vaccinated during the earlier phases of the vaccination rollout. For that reason, we conclude that a booster shot will be needed to maximize vaccine-induced protection and prolong its durability,” officials said.

The move is subject to an independent evaluation by the FDA to determine the safety and effectiveness of a third dose of the Pfizer and Moderna mRNA vaccines and CDC’s Advisory Committee on Immunization Practices issuing booster dose recommendations “based on a thorough review of the evidence.”

Officials said they anticipate booster shots will likely be needed for people who received the Johnson & Johnson vaccine, but they are still examining the evidence, with more data expected in the coming weeks

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Administration of the J&J vaccine did not begin in the U.S. until March, so boosters wouldn’t be needed until November at the earliest.

The announcement represents a rapid and dramatic shift in policy for the administration, which for months has been trying to tamp down a push for booster doses. Officials have repeatedly said it was not clear whether boosters would be needed.

In July, the CDC and FDA put out a joint statement that pushed back after Pfizer suggested booster shots.

“Americans who have been fully vaccinated do not need a booster shot at this time,” the agencies said.

But the messaging has softened in recent days. Last week, Fauci, the White House chief medical adviser, said it was “likely” everyone will need a coronavirus booster at some point.

The decision to provide boosters has significant implications domestically as well as abroad. Just more than 50 percent of Americans are fully vaccinated against the coronavirus, and while the pace of vaccinations has been increasing in recent weeks, millions are not vaccinated and have no interest in rolling up their sleeves.

Officials have tried to walk a fine line: They want to make sure the U.S. is prepared for any future COVID-19 complications while also prioritizing reaching the remaining unvaccinated.

The White House has also promised to be a world leader in donating the vaccine abroad, and officials Wednesday said that is not changing.

“I do not accept the idea that we have to choose between America and the world,” Surgeon General Vivek Murthy said during a press briefing.

“We clearly see our responsibility to both, and that we’ve got to do everything we can to protect people here at home while recognizing that ending the pandemic across the world and getting people vaccinated is going to be key to preventing the rise of future variants,” Murthy said.

Still, Murthy added that “when we see data that is giving us, essentially, indications that protection is starting to diminish …  we have to act.”