• The delta variant is the most closely watched coronavirus mutation yet and with good reason.
• Delta is more contagious than previous variants and there's evidence it increases the risk of hospitalization and is more resistant to vaccines.
• Data from England collected from February to June shows just who is most at risk.

The delta variant is the most closely watched coronavirus mutation yet and with good reason: It's more contagious than previous variants and there's evidence it increases the risk of hospitalization and is more resistant to vaccines.

The delta variant, first discovered in India late last year where it caused a second wave of infections and thousands of deaths, is now rapidly spreading throughout the world.

Last week, the World Health Organization warned that delta is the fastest and fittest coronavirus strain yet, and it will "pick off" the most vulnerable people, especially in places with low Covid-19 vaccination rates.

The U.K. is being closely watched by other countries, particularly the U.S., because it has seen the delta variant become dominant despite its high vaccination rate. It has also proved to be a harbinger of things to come during the pandemic, for good and bad.

Who's most at risk?

Now, data has been released in England showing just how far the delta variant has spread — and which groups are most vulnerable to the mutation.

Delta is dominant in the U.K., comprising 95% of all sequenced cases, according to the latest data from Public Health England, with younger people, the unvaccinated and the partially vaccinated (with many people belonging to one or more of those categories) more at risk from infection while older people are still most at risk of dying from an infection.

Number crunching the latest data from England, 92,029 cases were analyzed between early February and mid-June and were attributed to the delta variant.

Almost 82,500 of these total cases were recorded in people under 50 years old and a majority (53,822 cases) were found in unvaccinated individuals.

Among those cases in the unvaccinated cohort, the vast majority were in the under-50 age group (52,846 cases) and only 976 cases were in the over-50s.

Nonetheless, the data showed that there have been 117 deaths among people in England who had the delta variant with the majority being in the over-50 age group.

There have been eight fatalities among the under-50s with six of them in unvaccinated individuals and the other two in people who had received one dose.

What about vaccinations?

The data from England shows that cases of the delta variant were found in both partially and even fully vaccinated people, to a lesser extent, showing the importance of being fully vaccinated.

Out of the 92,029 total infections attributed to delta, almost 20,000 were recorded in people who had received one dose of a Covid vaccine (both before and following 21 days after a first dose) and 7,235 infections were confirmed in people who had received two doses.

The data serves as a reminder that no Covid vaccine currently on offer provides 100% protection, although most authorized vaccines currently come very close and experts are urging anyone not yet vaccinated to come forward, as well as the importance of having both doses to achieve the best protection possible.

Separate data from Public Health England has shown that two doses of the Pfizer-BioNTech or AstraZeneca-Oxford University shot are highly effective against hospitalization from the delta variant.

The U.K. has vaccinated its population according to age and health needs. Its vaccination program started with health-care workers and the elderly last December, progressing through the older age groups until the under-50s began to be offered Covid shots in mid-April.

Currently, all over-18s are being offered their first doses while others in their 30s and 40s are tending to receive their second doses; almost 85% of U.K. adults have now received one dose of a vaccine and 61.9% have received two doses, making it one of the most rapid vaccination programs in the world.

'Delta is predominant'

Updating its risk assessment on the delta variant published Friday, PHE said delta is "predominant" and "continues to demonstrate a substantially increased growth rate" compared with the alpha variant first discover in the U.K. which itself went on to dominate globally.

On just a weekly basis, data released by PHE last Friday showed that the number of cases caused by delta in the U.K. had risen by 35,204 since the previous week (representing a 46% increase) to a total of 111,157 cases.

We've published our weekly update on the number of new cases of #COVID19 #variants identified in the UK.

Numbers of the Delta variant have risen by 35,204 to a total of 111,157 - a 46% increase since last week.

Read more: https://t.co/BWDZ837z7p

— Public Health England (@PHE_uk) June 25, 2021

PHE noted that the delta variant also brings with it an increased risk of hospitalization compared with the alpha variant and there are now analyses from England and Scotland supporting earlier evidence that delta reduces vaccine effectiveness compared with the alpha variant, and that this is more pronounced when someone has received only one dose.

On a positive note, PHE reiterated that "analysis continues to show vaccine effectiveness against Delta is high after 2 doses" and that the evidence continues to suggest that vaccines are effective against hospitalization.