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AstraZeneca Vaccine May Cut Transmission of Virus
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They report that the effect of dosing interval on efficacy is pronounced, with vaccine efficacy rising from 54.9% with an interval of less than six weeks to 82.4% when spaced 12 or more weeks apart.
They also detail that a single standard dose of the vaccine is 76% effective at protecting from primary symptomatic COVID-19 for the first 90 days post vaccination, once the immune system has built this protection 22 days after the vaccination, with the protection showing little evidence of waning in this period.
overall cases of any PCR+ were reduced by 67% (95%CI 49%, 78%) after a single SD vaccine suggesting the potential for a substantial reduction in transmission.
AstraZeneca Vaccine May Cut Transmission of Virus
Feb 3 2021
https://www.nytimes.com/live/2021/02/03/world/covid-19-coronavirus#astrazeneca-coronavirus-vaccine
The vaccine developed by the University of Oxford and AstraZeneca has the potential to slow the transmission of the virus, according to a new paper.
The paper by researchers at the University of Oxford is the latest to report evidence suggesting that a coronavirus vaccine may be able to reduce transmission of the virus, though scientists have emphasized that the data are preliminary and the degree of protection unknown.
The researchers measured the impact on transmission by swabbing participants every week seeking to detect signs of the virus. If there is no virus present, even if someone is infected, it cannot be spread. And they found a 67 percent reduction in positive swabs among those vaccinated.
The paper, which has not been peer-reviewed, looked at data from clinical trials in Britain, Brazil and South Africa, the results of which were first reported late last year.
Matt Hancock, the British health secretary, hailed the results on Wednesday as "absolutely superb."
"We now know that the Oxford vaccine also reduces transmission and that will help us all get out of this pandemic," Mr. Hancock said in an interview Wednesday morning with the BBC.
The results, he said, "should give everyone confidence that this jab works not only to keep you safe but to keep you from passing on the virus to others."
Some scientists looking at the limited information released cautioned that more analysis of the data was needed before such broad conclusions could be firmly stated.
"While this would be extremely welcome news, we do need more data before this can be confirmed and so it's important that we all still continue to follow social distancing guidance after we have been vaccinated," said Dr. Doug Brown, chief executive of the British Society for Immunology.
The Oxford and AstraZeneca researchers also found that a single dose of the vaccine was 76 percent effective at preventing Covid-19. The data measured the three months after the first shot was given, not including an initial three-week period needed for protection to take effect.
The encouraging results, lend support to the strategy deployed by Britain and other countries to prioritize providing as many first doses of vaccines as possible, setting aside concerns that people will get their second doses later than initially planned.
The latest data do not have bearing on the debate over whether to further space out the doses of the two vaccines authorized in the United States, those from Pfizer-BioNTech and Moderna, since the data on AstraZeneca's candidate cannot be generalized to other vaccines.
Some scientists have called on the United States to follow the lead of Britain and other countries that have opted to delay the second doses of vaccines by up to 12 weeks. But U.S. federal officials have resisted, saying such a move would not be supported by the data from clinical trials of the two vaccines currently available across the nation. Tuesday's results could amplify pressure on U.S. health officials to delay second doses of AstraZeneca's vaccine, though it has not yet been authorized by the country.
The vaccine appeared more effective when the interval between the two shots was longer than the originally intended four-week gap, the Oxford and AstraZeneca researchers found. Among clinical trial participants who got two standard-strength doses at least three months apart, the vaccine was 82 percent effective, compared to 55 percent effective when the doses were given less than six weeks apart.
A vaccination strategy that spaces out doses by three months "may be the optimal for rollout of a pandemic vaccine when supplies are limited in the short term," the researchers wrote.
The newly released paper builds on data issued late last year, which found that the vaccine was 62 percent effective when given as two standard-strength doses. In those initial findings, the vaccine's efficacy was much higher, at 90 percent, when the first dose of the vaccine was given at half-strength.
Oxford and AstraZeneca researchers initially attributed the different levels of effectiveness to the lower strength of the initial dose. But they gradually reached a different conclusion: the amount of time between doses was the more likely explanation.
In the United States, the Food and Drug Administration is waiting on data from a clinical trial that enrolled about 30,000 participants, mostly Americans. Results from that study are expected later this month.
The study is expected to arm AstraZeneca with enough safety data to allow it by around early March to seek authorization to provide the vaccine for emergency use.
The United States has agreed to buy 300 million doses of AstraZeneca's vaccine, but neither the company nor the federal government has said when and in what quantities those doses will be available after the vaccine is approved.
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AstraZeneca vaccine may slow virus transmission
For now, the vaccine is not available in the United States.
February 3, 2021, 4:17 PM
https://abcnews.go.com/Health/astrazeneca-vaccine-slow-virus-transmission/story?id=75657579
The AstraZeneca vaccine likely slows the transmission of the virus in addition to protecting against severe COVID-19 illness and death, according to a new study.
Single Dose Administration, And The Influence Of The Timing Of The Booster Dose On Immunogenicity and Efficacy Of ChAdOx1 nCoV-19 (AZD1222) Vaccine
To come to that conclusion, University of Oxford researchers swabbed study participants in the U.K. every week and found a 67% reduction in positive swabs among participants who had been vaccinated.
"We haven't specifically measured transmission because that's a different type of study," Andrew Pollard, head of the Oxford Vaccine Group said during a Wednesday press briefing. "What we've got is a study which tells the number of people who are no longer infected and if you're not infected there's an assumption that you can't then transmit the virus."
While the preliminary research was published in The Lancet Tuesday, the study itself has not yet been peer reviewed by external experts.
"The vaccine reduced by two-thirds the likelihood that people would carry, and hence be able to spread the virus," said Dr. William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University Medical Center. "That's a very exciting piece of information," he added.
"It's the first solid information that a vaccine not only protects the individual, but reduces the spread of the virus from person to person," Schaffner said, which is key for eventually reaching herd immunity, where enough people have immunity that it affords protection to the rest of the population.
Although the new results are promising, the United States has opted not to move forward with the AstraZeneca vaccine until it has more data on it. The Food and Drug Administration has said that it is waiting to see results from a 30,000-person clinical trial that's ongoing in the U.S. before it moves forward with considering an emergency use authorization like it did for the Pfizer and Moderna vaccines. Data should be available by the end of the month.
The U.S. invested $1.5 billion to secure 300 million doses of the AstraZeneca vaccine last spring, assuming the vaccine is eventually authorized.
European countries have been similarly cautious about AstraZeneca's data, which has been criticized for lacking detail and transparency. On Wednesday, Switzerland declined to authorize the AstraZeneca vaccine, calling the data that's been submitted and analyzed so far "not yet sufficient."
"To obtain more information about safety, efficacy and quality, additional data from new studies are needed," the country's drug regulator, Swiss Agency for Therapeutic Products, said in a statement.
"Once those data are in we'll have to look at them very, very carefully," Schaffner said. For now, he hopes the AstraZeneca news is a preview of what's to come for vaccines like Pfizer and Moderna. "We think it bodes well for the other vaccines, but we can't say for sure," he added.
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