The Indian Delta variant of the virus that causes Covid-19 doubles the risk of hospitalisation compared to the Alpha variant it has supplanted as the dominant strain worldwide, researchers reported Saturday in The Lancet.

Only 1.8 percent of the more than 43,000 Covid cases assessed in comparing the two variants were in patients who had been fully vaccinated.

Three-quarters were completely unvaccinated, and 24 percent had only received one jab of a two-dose vaccine.

"The results from this study therefore primarily tell us about the risk of hospital admission for those who are unvaccinated or partially vaccinated," said co-lead author Anne Presanis, a Senior Statistician at the University of Cambridge's MRC Biostatistics Unit.

Researchers analysed healthcare data from 43,338 COVID-19 cases in England from March 29 to May 23 of this year, including vaccination status, emergency care, hospital admission and other patient information. 

All virus samples underwent whole genome sequencing, the surest way to confirm which variant had caused the infection.

Just under 80 percent of the cases were identified as the Alpha variant, and the rest were Delta.

Around one in 50 patients were admitted to hospital within 14 days of their first positive COVID-19 test. 

After accounting for factors that are known to affect susceptibility to severe illness -- including age, ethnicity, and vaccination status -- the researchers found the risk of being admitted to hospital was more than doubled with the Delta variant.

- 'Excellent protection' -
Since these samples were taken, Indian Delta has surged and now accounts for over 98 percent of new Covid-19 cases in Britain, the authors said.

Multiple studies have shown that full vaccination prevents infection with symptoms and hospitalisation, for both Alpha and Delta variants.

"We already know that vaccination offers excellent protection against Delta," said Gavin Dabrera, another lead author and a consultant epidemiologist at the National Infection Service, Public Health England.

"It is vital that those who have not received two doses of vaccine do so as soon as possible." 

An earlier study from Scotland also reported a doubling in hospitalisation risk with Delta over Alpha, suggesting that Delta causes more severe disease. 

The Delta variant was first reported in India in December 2020 and early studies found it to be up to 50 percent more transmissible than the Alpha variant, which was first identified in England in September last year.

Nearly 4.5 million deaths worldwide have been attributed to Covid-19, though the final tally is likely to be higher once "excess deaths" are calculated over the pandemic period.

In some countries -- and some states in the United States -- hospitalisation and death rates are the highest they have been since the first cases reported at the beginning of 2020.

India vaccinates 10 million in one day
India has given more than 10 million Covid-19 jabs in a single day for the first time, authorities said Saturday, as the South Asian giant bolsters its defences for a predicted new surge.

The health ministry said the 10 million landmark was passed on Friday, beating the country's previous daily record of 9.2 million. The government has been stung by criticism after a brutal coronavirus wave in April and May killed more than 200,000 people.

Prime Minister Narendra Modi hailed the milestone as a "momentous feat" for the nation of 1.3 billion people.

"Kudos to those getting vaccinated and those making the vaccination drive a success," he said on Twitter.

The government had aimed to vaccinate about 1.1 billion adults by the end of the year but shortages, administrative confusion and hesitancy have held back numbers. Only around 15 percent have had two doses since the drive began in January.

India's daily infection count has dropped dramatically since the devastating surge in April-May which overwhelmed its creaking health infrastructure.

Almost all restrictions on movement and activity have been lifted even though experts have warned of a new wave hitting as early as next month as the festival season starts.

Daily case numbers have started rising again above 40,000 and more than 500 deaths were reported on Saturday. The 46,000 new cases reported Saturday was the highest figure in two months. Much of the spike has been blamed on a surge in the southern state of Kerala.

India is currently administering three vaccines -- the Oxford-AstraZeneca jab, known locally as Covishield, Covaxin by Indian firm Bharat Biotech and the Russian-made Sputnik V.

The country has so far recorded 437,370 deaths and more than 32 million infections, the second-highest in the world after the United States. Experts say that because of under-reporting, India's true toll could be more than four times higher.