Story at a glance

  • The vaccine developed by AstraZeneca and the University of Oxford boasts a 76 percent efficacy rate after a single dose.
  • It notes that administering the second dose with a longer interval between shots resulted in higher efficacy levels.

Drugmaker AstraZeneca released results Wednesday from its COVID-19 vaccine clinical trials, demonstrating increasing efficacy after a single dose of the vaccine.

The results indicate that a single dose of AstraZeneca’s vaccine candidate results in an efficacy of 76 percent. When given a second dose over a longer interval, about 12 weeks or more, the vaccine’s efficacy rate rose to 82 percent.

Researchers used a placebo-controlled study to evaluate the results. Within the group that received vaccinations, there were no hospitalizations, whereas 15 were reported in the control group.

Phase 3 clinical trials were conducted in the U.K., Brazil, and South Africa — all countries with reports of new, more contagious COVID-19 strains.

Trials also show that the vaccine could potentially reduce the spread of the virus in addition to preventing people from developing symptoms. AstraZeneca reports that, based on weekly swabs from volunteers in the U.K., positive cases were reduced by 67 percent after a single dose and 50 percent after the second dose, an optimistic sign that the vaccine has substantial effect on transmission of the virus.


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A more detailed report, published in the medical journal The Lancet, noted that in the more than 17,000 subjects who participated in the trial, binding antibody responses were significantly higher following a two-dose interval of 12 weeks as opposed to less than six weeks. 

“This primary analysis reconfirms that our vaccine prevents severe disease and keeps people out of hospital,” said Sir Mene Pangalos, executive vice president of BioPharmaceuticals R&D at AstraZeneca. “In addition, extending the dosing interval not only boosts the vaccine’s efficacy, but also enables more people to be vaccinated upfront. Together with the new findings on reduced transmission, we believe this vaccine will have a real impact on the pandemic.”

Vaccine doses from Pfizer and Moderna currently administered in the U.S. are given about three weeks apart.

Last week, Johnson & Johnson released similar vaccine data, implying a high efficacy rate with just a single dosage of their vaccine. 

Additionally, clinical trial data suggests that the vaccine may have a “substantial effect” on cutting transmission of the virus. Polymerase chain reaction (PCR) tests samples from a portion of the U.K. volunteers noted a 67 percent reduction in confirmed infections. 

Observing the volume of positive PCR tests is an effective epidemiological strategy to gauge the transmission rate of a virus within a population. The fewer positive results imply a decreased virus spread. 

“These new data provide an important verification of the interim data that has helped regulators such as the MHRA in the UK and elsewhere around the world to grant the vaccine emergency use authorisation,” Professor Andrew Pollard, Chief Investigator of the Oxford Vaccine Trial, commented. “It also helps to support the policy recommendation made by the Joint Committee on Vaccination and Immunisation for a 12-week prime-boost interval, as they look for the optimal approach to roll out, and reassures us that people are protected 22 days after a single dose of the vaccine.”

AstraZeneca is now seeking emergency use approval from the World Health Organization. 

Similarly to other vaccines, it must be stored in cool temperatures at 2 to 8 degrees Celsius.


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Published on Feb 03, 2021