Delta Covid variant 'seeded' into Scotland through most affluent communities

Their findings also highlight "concerning" data showing that the proportion of fully vaccinated people requiring hospital treatment, while low, is higher with the Delta variant compared to the previously dominant Alpha ('Kent') variant.

It comes as Prime Minister Boris Johnson confirmed a four-week delay to the final lifting of restrictions in England, to July 19, to enable a higher proportion of the population to get second doses and allow longer for immunity to build up.

READ MORE: 761 new Covid cases reported in Scotland 

First Minister Nicola Sturgeon is due to give an update on the Covid situation in Scotland tomorrow, with a scheduled move to Level Zero nationally from June 28 also likely to be pushed back.

The latest research, which has been peer-reviewed, was carried out by scientists at the universities of Edinburgh and Strathclyde in collaboration with Public Health Scotland.

It is part of the ongoing EAVE II project which is using anonymised patient data for 5.4 million in Scotland to track the effect on vaccinations on the pandemic in real-time.

The latest data covers the period from April 1 to June 6 and shows that the Delta variant overtook Alpha in terms of prevalence on May 19.

Co-author Chris Robertson, a professor of public health epidemiology and a member of the Scottish Government Covid-19 advisory group, said initial Delta infections - also known as "S-positive" cases - had been clustered in the least deprived areas.

This contrasted with the Alpha variant, where around 30% of infections have been occurring in the poorest fifth of postcodes.

However, Prof Robertson - who has been monitoring the trend for the past four weeks - said the Delta pattern was shifting as cases spread more widely through the population.

He said: "When the Delta variant came across in Scotland, the deprivation curve was actually slightly higher in the least deprived communities and that likely represents whereabouts it was seeded in Scotland - so it tended to be seeded in the more affluent areas.

"Over that four week period the curve has shifted slightly more down towards the more deprived areas and I would expect that, in a couple of weeks time, the curve will be identical [to Alpha]."

The first known cases of the Delta variant were detected in the UK in February but India was not placed on the red list for travel until April 23.

During the study period, a total of 19,543 Covid infections were recorded in Scotland where the causal variant was identified. Of these, 7,725 were caused by the Delta strain and 134 people were hospitalised with the infection.

The vast majority of Delta infections - 70% - occurred in people who were unvaccinated.

Compared to the Alpha variant, the researchers found that those infected with the Delta strain were nearly twice as likely to end up in hospital once adjusting for factors such as age, sex, deprivation, vaccination status and co-morbidities.

The vast majority requiring hospital treatment were unvaccinated younger people who tended to become less sick and recover more quickly, but there were also indications of higher "vaccine failure" rates in relation to Delta infections.

Around 5% of Delta hospital admissions were fully vaccinated, compared to around 2% of those whose infections were caused by the Alpha variant.

Prof Robertson said this was "concerning" and while monitoring is still ongoing, it is likely that most of these vaccine failure cases are occurring in people who are elderly or with pre-existing conditions that weaken their immune systems.

Both main vaccines continue to reduce the risk of Covid infection but this effect "appeared to be diminished" for the Delta variant compared to the Alpha strain, said researchers.

READ MORE: One in 20 Covid infections in patients already fully vaccinated 

In community cases with or without symptoms where individuals had been fully vaccinated at least two weeks prior to testing positive, the Pfizer-BioNTech vaccine was found to provide 79% protection against the Delta variant compared to 92% against the Alpha variant.

The Oxford-AstraZeneca vaccine provided 60% protection against the Delta variant compared to 73% against the Alpha strain.

Efficacy against a Delta Covid infection also fell to just 18% (AstraZeneca) and 30% (Pfizer) 28 days after a first dose, although the researchers said it was "challenging" to draw a direct comparison between the two vaccines at this stage because they had been administered to different demographic groups.

Co-author Aziz Sheikh, a professor of primary care at Edinburgh University and member of the Scottish Government's Covid-19 advisory group, said it was still clear that vaccines are "the surest way out" of the pandemic but said the findings underline the importance of making sure that as many people as possible are fully vaccinated before lockdown ends.

Prof Aziz said: "Any sort of increase in the window of opportunity before lockdown measures are completely brought to an end will be helpful because that will help us to control community transmission, so I would be very supportive of any delays that might be announced."

Dr Jim McMenamin, of Public Health Scotland, stressed that "the more people who have taken up their second dose the less likely that we'll see significant hospital pressures as a consequence of Covid."

He added: "The Delta variant does increase the risk of hospitalisation. However, what we are able see from the information available to us is that our vaccines are still highly effective.

"Two doses still provides strong protection against the risk of hospitalisation or the risk of infection in the community, so that means we've got an opportunity to counter the threat of this Delta variant by encouraging uptake of both doses of the vaccine.

"That means if you have had your first dose there's an incredibly strong message here to come forward and get your second dose.

"If you as yet have not come forward to be vaccinated, you need to come forward for both doses of vaccine when they are offered to you."