It spreads more easily, it's more severe, and it's more resistant to vaccines.
More than a year-and-a-half since Covid-19 emerged in China – sparking a global pandemic that has crippled economies, killed millions and forced international borders closed – there are growing fears that the Indian strain of the virus could derail long-awaited re-openings and plunge the world back into crisis.
The so-called Delta variant, which was first detected in India last October, has now spread to at least 62 countries and is behind a growing number of outbreaks across Asia and Africa, the World Health Organisation said this week.
In the UK, the Delta variant – given the new name by the WHO to simplify its scientific name, B.1.617.2, and to avoid stigmatising countries that detect new strains – now accounts for 90 per cent of new cases, which have begun to surge again despite a successful vaccination campaign.
On Friday, Britain recorded 8125 new cases nationwide, the highest daily number in four months and a 58 per cent weekly increase, with 158 people hospitalised.
The disturbing figures are forcing the UK Government to consider delaying the final easing of restrictions on June 21 by either two or four weeks, The Times reported.
The goal is to give people more time to get their second shot. Around 75 per cent of the UK has been vaccinated, but only 40 per cent have had two doses.
Figures published this week showed the two-thirds of the 383 hospitalisations from the Delta variant were people who had not been vaccinated, while there had been 42 hospitalisations and 12 deaths in people who had received both doses of the vaccine.
"This is about giving people certainty," a Government source told The Times. "The worst-case scenario is that we ease restrictions and then have to implement them again. This has to be a one-way ticket."
British Prime Minister Boris Johnson is expected to wait until Sunday to look at the figures and make a final decision to be announced, according to the paper, but a delay is widely expected.
The Sun newspaper reported late on Friday that Johnson was set to delay "freedom day" to July 19.
Johnson told world leaders at the G7 summit on Friday that "we need to make sure we don't repeat some of the errors that we have made in the course of the last 18 months".
Anthony Costello, a British paediatrician and member of the Independent SAGE advisory group, told the BBC earlier this month that June 21 was too early to ease restrictions.
He noted that the Delta variant was thought to be 50 to 70 per cent more transmissible, had a 2.7 times higher likelihood of hospitalisation, and showed evidence of "vaccine escape".
"If you have had one dose of the vaccine, you are only 34 per cent protected," Dr Costello said.
"If you've had two doses, you're only about two-thirds protected. That means there are millions and millions of people who could be infected by this virus. Now, many of them will be younger, and death rates should be much, much lower. But many people could end up in hospital, the NHS could be thrown into another surge – we just don't know."
In addition to the higher transmissibility, there are anecdotal reports from India that the Delta variant is more severe in children than the so-called Alpha strain.
And doctors treating patients in India have reported disturbing new symptoms, including gangrene and hearing loss.
A YouGov poll published by The Times on Saturday found the majority of British voters supported pushing back the June 21 reopening.
The poll found 53 per cent said restrictions should remain beyond June 21, with 34 per cent saying they should end.