‘Intensity’ of Delta importations from overseas set UK on course for sharp rise in Covid cases, say experts

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Figures suggest that at least 20,000 passengers who could have been infected with Delta arrived between 2 April and 23 April (AFP/Getty)
Figures suggest that at least 20,000 passengers who could have been infected with Delta arrived between 2 April and 23 April (AFP/Getty)

The “intensity” with which cases of the Delta coronavirus variant were introduced to the UK set the country on course for the sharp rise in infections now being recorded, leading scientists have said.

Experts believe the Delta variant is 60 per cent more transmissible than the Alpha strain, which first emerged in Kent last year, and is fuelling the increase in cases recorded over the past three weeks.

Infections appear to be rising exponentially once again. Some 7,540 cases were reported on Wednesday – the highest daily count since 27 February. Hospitalisations are also creeping up, though remain well below the peak seen during the winter wave.

The government has faced widespread criticism for its failure to act quickly against the spread of the Delta variant, which first surfaced in India last year.

Prime minister Boris Johnson has been accused of being slow to ban travel to and from India, even as cases of the variant surged in the country.

It’s believed the PM was initially reluctant to close the border to travellers for political reasons, with Mr Johnson afraid of offending India’s prime minister Narendra Modi while a trade deal was in the works – something that Downing Street has strongly denied.

India was added to the UK’s “red list” on 23 April, despite having a larger number of cases than Pakistan and Bangladesh when flights to the two countries were banned three weeks earlier.

As a result of this delay, experts believe a large number of Delta cases were imported to the UK, leading to widespread seeding of infection.

Civil Aviation Authority figures suggest that at least 20,000 passengers who could have been infected with Delta arrived from India between 2 and 23 April.

Explaining why the UK appeared to be the only country in Europe to have recorded a surge in Delta cases, Dr Jeffrey Barrett, a leading statistical geneticist, told reporters: “I think a part of it is that the UK got the intensity of importation over a period of few weeks that set us on this trajectory.

“I don’t have an easy answer. I think a big part of it is random chance ... If you get one introduction, even of a transmissible variant, there’s a decent chance it fizzles [out] and doesn’t create a big outbreak.

“If you get 100, 500 or 1,000 introductions, it’s very hard to avoid that some of them will go on to seed big outbreaks.”

He pointed to the example of Denmark, which has “had repeated small numbers of introductions of the Delta variant” over the same period as the UK. But the country’s epidemic “hasn’t grown at all”, said Dr Barrett, who is also director of the Covid-19 Genomics Initiative at the Wellcome Sanger Institute.

He said he suspected that Delta would eventually spread to other countries in the same way as the Alpha variant did. “It will move from country to country over some slightly difficult-to-predict timeframe, but I suspect it will spread globally over time,” Dr Barrett said.

The US will be the next country that “probably” sees a “reasonable rise”, he added. “If you look at the US data, it’s starting to go up there.”

Professor Neil Ferguson, an epidemiologist at Imperial College London, said he “completely” agreed with the hypothesis.

“We had a large number of cases imported into the country at a time point when background incidence of Covid was really quite low,” he told a media briefing on Wednesday.

The fact that the UK has powered ahead with its vaccination programme compared to other European countries will also have played in Delta’s favour in terms of outcompeting the previously dominant Alpha strain, Prof Ferguson said.

“It’s a partial-immune-escape variant,” he added. “So vaccine efficacy is reduced. It can transmit more easily in a vaccinated population than the Alpha variant.”

Prof Ferguson said that up to a quarter of the Delta variant’s transmissibility edge over Alpha might come from its ability to evade the body’s immune response, saying it was “a contribution, but not an overwhelming contribution” to its advantage.

Professor Wendy Barclay, a virologist at Imperial College London, said she believed it was “somewhat inevitable that this variant would take off if introduced enough into a country”.

The latest modelling from the Scientific Pandemic Influenza Group on Modelling (SPI-M), which advises the government, meanwhile suggests there is a “substantial” risk of a third wave of infections – one that could rival Britain’s winter surge, said Prof Ferguson.

He added that it was unclear, however, how any spike in hospitalisations would translate into a rise in deaths, as more detail was needed on how well the vaccine protects against serious illness from Delta.

“It’s well within possibility that we could see another third wave at least comparable in terms of hospitalisations,” he said. “I think deaths probably would be lower; the vaccines are having a highly protective effect... still it could be quite worrying. But there is a lot of uncertainty.”

Data from Public Health England has shown that the Delta variant reduces the effectiveness of the Pfizer and AstraZeneca vaccines among those who have only received one shot, though protection is higher for those who have received both doses.

The shadow home secretary Nick Thomas-Symonds said: “The Conservatives left the door open to Covid and new variants. Ministers were warned time and time again that we needed a proper hotel quarantine system and that India was added to the red list far too late. Now it is clear that tens of thousands of people entered the UK with the Delta variant thanks to Conservative incompetence. This has put the reopening on 21 June at risk – and ministers have only themselves to blame.”

Layla Moran, the chair of the All Party Parliamentary Group (APPG) on coronavirus, said: “This latest rise in cases is deeply concerning and again is a result of the government’s failure to act at the appropriate moment, now leaving the country at risk of a third wave of infections.

“Our cross-party report published in May called for countries to be added to the ‘red list’ as soon as variants of concern are identified. The importation of the Delta variant was entirely avoidable.

“The government must rethink its flawed approach to international travel and focus on preventing the importation of variants, so that our hard-won progress against the virus is not thrown away yet again.”

Liberal Democrat health spokesperson Munira Wilson said: “It’s clear that throughout this pandemic, Boris Johnson has been slow to act. The spread of the Delta variant in the UK is only the latest example of his mishandling of this crisis and a timely reminder of the importance of testing and tracing cases of this disease.

“India should have been added to the ‘red list’ as soon as it became clear that the risk of the variant had drastically increased, and the government should have tracked every case down as soon as they were aware of it.

“The government cannot continue failing to slow the spread of the virus. They need to get test and trace working effectively, increase support for those self-isolating, both financially and practically, and do everything in their power to prevent new variants entering the country.”

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