The Delta variant of Covid-19, or the B1.617.2 variant of concern (VOC), first identified in India although it arrived from the UK, is about 60% more transmissible than the Alpha strain identified in Britain. It reduces the effectiveness of vaccines to some extent, UK health experts report on 11 June.
Public Health England (PHE), which has been tracking VOCs on a weekly basis, said that the cases of the Delta VOC have risen by 29,892 to hit 42,323 in the country an increase of around 70%.
The latest data indicates that over 90% of new Covid-19 cases in the UK are now the Delta variant, which continues to show a significantly higher rate of growth compared to the Alpha VOC which was first identified in the region of Kent in England and was the dominant variant in the country so far.
“New research from PHE suggests that the Delta variant is associated with an approximately 60 per cent increased risk of household transmission compared to the Alpha variant. Growth rates for Delta cases are high across the regions, with regional estimates for doubling time ranging from 4.5 days to 11.5 days,” PHE said in its latest analysis.
“There are now analyses from England and Scotland supporting a reduction in vaccine effectiveness for Delta compared to Alpha. This is more pronounced after one dose (absolute reduction in vaccine effectiveness against symptomatic infection of approximately 15% to 20% after one dose),” its risk assessment analysis reads.
“Iterated analysis continues to show vaccine effectiveness against Delta is higher after two doses but that there is a reduction for Delta compared to Alpha. There is uncertainty around the magnitude of the change in vaccine effectiveness after two doses of Oxford-AstraZeneca vaccine,” it said.
PHE said that with the Delta variant now accounting for the overwhelming majority of new cases in the UK, it is “encouraging” to see that the increase in cases is not yet accompanied by a similarly large increase in hospitalisations.
“PHE will continue to monitor closely over the next few weeks, but the data currently suggest that the vaccination programme continues to mitigate the impact of this variant in populations who have high two dose vaccine coverage,” it said.
The health experts are using novel genotyping tests to detect the Delta VOC, giving a result for action within 48 hours. Positive tests identified through this process are subsequently confirmed through full genome sequencing and PHE says that recent data have shown them to be extremely accurate in indicating a positive variant result.
“With numbers of Delta variant cases on the rise across the country, vaccination is our best defence. If you are eligible, we urge you to come forward and be vaccinated. Remember that two doses provide significantly more protection than a single dose,” said Dr Jenny Harries, Chief Executive of the UK Health Security Agency.
“However, while vaccination reduces the risk of severe disease, it does not eliminate it. With data showing that Delta is significantly more transmissible than Alpha, it is just as important as ever to follow public health advice, which has not changed. Get vaccinated, work from home where you can and remember ‘hands, face, space, fresh air’ at all times. These measures work, and they save lives,” she said.
The latest data comes as the UK government is set to announce its plans on Monday on whether the roadmap to lifting all lockdown restrictions by 21 June can go ahead.
There are growing voices from within the scientific community calling for a delay to that date in order to administer further second doses of vaccines for the over-50s, to ensure greater protection against the Delta variant.