Double vaccinated 'can easily spread Delta variant in households'

Researchers say unvaccinated should take shot as soon as possible as winter months draw in

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  Not all commuters on the Underground in London choose to wear masks. UK government ministers are under pressure to implement 'Plan B' winter measures to address rising Covid-19 case numbers and a faltering booster vaccine programme. AFP

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  Health workers at a Covid-19 PCR test centre in London. Britain's daily coronavirus case numbers and the seven-day rolling average reached their highest level in three months in October. EPA

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  A man receives a Covid-19 vaccine at Regent Pharmacy in Northampton. There are concerns over a sluggish booster shot programme for over-50s and low uptake of vaccines among 12 to 15-year-olds. Reuters

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  Britain's Health Secretary Sajid Javid with UK Health Security Agency chief executive, Dr Jenny Harries, during a press conference at Downing Street. Getty Images

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  The National Covid Memorial Wall in London. Under UK Prime Minister Boris Johnson’s winter plan announced in September, Plan B would include a return to working from home for many, mandatory mask-wearing in some settings and vaccine certificates required at large indoor gatherings. Reuters

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  A demonstration in Parliament Square, London, against Covid-19 vaccine passports and British government restrictions to curb the spread of coronavirus. AP Photo

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  Passengers on a London Underground train on the Jubilee Line, where face coverings are required to be worn. AP Photo

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  Bus passengers in London. Masks are not mandatory in indoor settings such as shops, restaurants and bars in England. AP Photo

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  A section of the National Covid Memorial Wall – a dedication of thousands of hand-painted hearts and messages commemorating victims of the Covid-19 pandemic. Reuters

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  An NHS Covid-19 vaccination campaign advertisement near a housing block in London. Reuters

Double vaccinated people can easily spread the Delta variant of Covid-19 in their households, a British study has shown.

Unvaccinated people were most at risk of transmission, the Imperial College London study found. Contacts were less likely to get infected if they had been vaccinated.

The study illustrates how the highly transmissible Delta variant can spread even in a vaccinated population.

Peak viral load among vaccinated people is similar to that seen in unvaccinated people, which may explain why they can still readily pass on the virus, according to the study published in The Lancet Infectious Diseases.

Researchers say unvaccinated people should get their shot as soon as possible, with people now more likely to spend time indoors due to the winter months.

Vaccines remain highly effective at preventing severe disease and deaths from Covid-19 but studies suggest they may be less effective against the Delta variant.

The researchers underlined that did not weaken the argument for vaccination as the best way of reducing serious illness from Covid-19 and said booster shots were required.

“By carrying out repeated and frequent sampling from contacts of Covid-19 cases, we found that vaccinated people can contract and pass on infection within households, including to vaccinated household members,” Dr Anika Singanayagam, co-lead author of the study, said.

“Our findings provide important insights into ... why the Delta variant is continuing to cause high Covid-19 case numbers around the world, even in countries with high vaccination rates.”

“The ongoing transmission we are seeing between vaccinated people makes it essential for unvaccinated people to get vaccinated to protect themselves from acquiring infection and severe Covid-19, especially as more people will be spending time inside in close proximity during the winter months,” Dr Singanayagam said.

The study, which enrolled 621 participants, found that of 205 household contacts of people with Delta per cent Covid-19 infection, 38 of household contacts who were unvaccinated went on to test positive, compared to 25 per cent of vaccinated contacts.

A patient receives a Covid-19 vaccine booster which are critical to overcoming the threat from Covid-19 variants

Vaccinated contacts who tested positive for Covid-19 on average had received their shots longer ago than those who tested negative, which the authors said was evidence of waning immunity and supported the need for booster shots.

Imperial College London epidemiologist Neil Ferguson said that the transmissibility of Delta meant that it was unlikely Britain would reach “herd immunity” for long.

“That may happen in the next few weeks: if the epidemic's current transmission peaks and then starts declining, we have by definition in some sense reached herd immunity, but it is not going to be a permanent thing,” he told reporters.

“Immunity wanes over time, it is imperfect, so you still get transmission happening, and that is why the booster programme is so important.”