The delta coronavirus variant is significantly likelier to lead to hospitalization than even the dangerous alpha variant, according to two new studies.

The new evidence arrived as the United Kingdom announced plans to delay its reopening due to the spread of the delta variant, which was first discovered in India.

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Delta variant significantly increases hospitalization risk

For the first study, published as a research letter in The Lancet, researchers in Scotland looked at tests of 5.4 million people in Scotland, including 7,723 Covid-19 cases and 134 hospitalizations, between April 1 and June 6.

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The researchers found the delta variant doubled a person's risk of hospitalization with Covid-19 compared with the alpha variant, which was first discovered in the U.K. and which research suggests already carried a higher risk of hospitalization and death than the original coronavirus strain.

However, the researchers also found that receiving both doses of two-dose vaccines provided strong protection against the delta variant.

Specifically, the Pfizer-BioNTech vaccine provided 79% protection against any confirmed infection with the variant at least two weeks after the second dose, while the AstraZeneca-Oxford University vaccine provided 60% protection, the researchers found.

Vaccines appear to be even more effective at preventing severe delta variant infections that lead to hospitalization, according to separate data from Public Health England (PHE). The data, based on an analysis of 14,019 delta variant cases between April 12 and June 4, found that, after two doses, the Pfizer-BioNTech vaccine was 96% effective at preventing hospitalization, while the AstraZeneca-Oxford vaccine was 92% effective at preventing hospitalization.

According to PHE, vaccine efficacy against the delta variant was "comparable" to efficacy against the alpha variant.

UK delays reopening due to delta variant concerns

The studies come as U.K. Prime Minister Boris Johnson on Monday announced the country will delay its plan to scale back coronavirus restrictions by four weeks in response to increasing Covid-19 cases and hospitalizations, which are largely driven by the delta variant.

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The U.K. is currently averaging about 8,000 cases per day, and case rates are doubling each week in the most severely affected areas, the New York Times reports.

Of the 33,000 delta variant cases logged in the U.K. so far, more than half have occurred in unvaccinated individuals, the Wall Street Journal reports. Of the 383 people hospitalized with Covid-19 stemming from the delta variant, two-thirds were unvaccinated, while about one-fifth had received only a single dose of a Covid-19 vaccine.

The delay in reopening means that certain U.K. businesses, such as nightclubs, will remain closed, the sizes of gatherings will remain restricted, and masking and social distancing requirements will remain in place.

According to scientists advising the U.K. government, modeling suggests that a four-week delay in reopening will reduce hospital admissions by between one-third and a half.

Johnson said he's "confident" there won't be any more delays, and the U.K. government said it will revisit its delay plan after two weeks. A spokesperson for the government said that, by July 19, everyone over the age of 40 will be able to receive a second dose of a Covid-19 vaccine—averting the need for any further delays.

"Now is the time to ease off the accelerator," Johnson said. "By being cautious now, we have the chance in the next four weeks to save many thousands of lives by vaccinating millions of people" (Collis, Politico, 6/14; Douglas/Bhattacharya, Wall Street Journal, 6/14; Douglas, Wall Street Journal, 6/14; Webber, Politico, 6/14; Castle/Mueller, New York Times, 6/14).