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The AstraZeneca vaccine is shown to dramatically cut transmission of the virus.

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Developed by Oxford University and AstraZeneca, the vaccine not only protects people from serious illness and death, but also significantly slows down the transmission of the virus, according to a new study – a finding that underscores the importance of mass vaccination as a way out of the pandemic.

The study by researchers at Oxford University is the first to document evidence of this Any coronavirus vaccine can reduce the transmission of the virus.

Researchers measured the effects on transmission by wiping participants down each week to look for signs of the virus. In the absence of a virus, it cannot be spread even if someone is infected. And they found a 67 percent reduction in positive swabs among those vaccinated.

The results, detailed by Oxford and AstraZeneca researchers in a non-peer-reviewed manuscript, found that the vaccine could reduce transmission by nearly two-thirds.

Matt Hancock, the UK Health Secretary, hailed the results on Wednesday as “absolutely outstanding”.

“We now know that the Oxford vaccine will also reduce transmission and help us all get out of this pandemic,” Hancock said in an interview with the BBC on Wednesday morning.

The results, he said, “should give everyone confidence that this shock will not only serve to protect you, but also to keep you from passing the virus on to others.”

The Oxford and AstraZeneca researchers also found that a single dose of the vaccine was 76 percent effective against Covid-19. The data was measured three months after the first shot, with no initial three week period required for the protection to take effect.

The encouraging results support the UK and other countries’ strategy of prioritizing the provision of as many first doses of vaccine as possible, ignoring concerns that people will receive their second doses later than originally planned.

The latest data does not affect the debate over whether to further reduce doses of the two US-approved vaccines Pfizer-BioNTech and Moderna, as the data on AstraZeneca’s candidates cannot be transferred to other vaccines.

Some scientists have urged the United States to follow the example of the UK and other countries who have chosen to postpone the second dose of vaccine for up to 12 weeks. But U.S. federal officials refused, saying such a move would not be supported by clinical trial data for the two vaccines currently available nationwide. Tuesday’s results could add to pressure on US health officials to postpone AstraZeneca’s second dose of vaccine, even though it has not yet been approved by the country.

The vaccine appeared to be more effective when the interval between the two shots was longer than the originally intended four weeks, the researchers at Oxford and Astrazeneca found. Among clinical trial participants who received two standard strength doses at least three months apart, the vaccine was 82 percent effective, compared with 55 percent when the doses were given less than six weeks apart.

A vaccination strategy that cuts doses by three months “might be the optimum for pandemic vaccine rollout when supplies are limited in the short term,” the researchers wrote.

The newly published study builds on data published late last year. The vaccine was found to be 62 percent effective at two standard strength doses. In these initial findings, the vaccine effectiveness was 90 percent much higher when the first dose of the vaccine was given at half strength.

The researchers from Oxford and AstraZeneca initially attributed the different levels of effectiveness to the lower strength of the initial dose. Gradually, however, they came to a different conclusion: the time between doses was the more likely explanation.

In the United States, the Food and Drug Administration is waiting for data from a clinical trial that involved around 30,000 participants, mostly Americans. The results of this study are expected later this month.

The study is expected to provide AstraZeneca with enough safety data to enable it to obtain approval to make the emergency vaccine available by early March.

The United States has agreed to purchase 300 million doses of the vaccine from AstraZeneca, but neither the company nor the federal government has indicated when and in what quantities those doses will be available after the vaccine is approved.

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Robert Dunfee