AstraZeneca Clarifies: Vaccine Shown to Be 76% Effective in Results From US Clinical Trial

Update, March, 25, 2021: After pushback from US health officials and the National Institute of Allergy and Infectious Diseases claiming AstraZeneca referenced outdated information for interim analysis of vaccine efficacy in the phase 3 US clinical trial on Monday, the company released updated metrics stating the two-dose COVID-19 vaccine candidate proved to be 76 percent effective in preventing symptomatic COVID-19. This is slightly lower than 79 percent, the metric initially released. The company maintains that the shot is 100 percent effective against severe disease and hospitalization (a good sign).

"Positive high-level results from the primary analysis of the Phase III trial of AZD1222 in the US have confirmed vaccine efficacy consistent with the pre-specified interim analysis announced on Monday 22 March 2021," a statement reads. "The vaccine was well tolerated, and no safety concerns related to the vaccine were identified." This new data is based on 190 symptomatic cases in the trial as opposed to 141 from Monday's report, and the efficacy of the vaccine proved to be 85 percent in adults 65 and older (an increase from 80 percent in Monday's data).

The company had said the numbers published on Monday were based on a "pre-specified interim analysis" of data that was cut off by Feb. 17 and vowed to issue an update (which it did); however, the company also announced that there are 14 "additional possible or probable cases" to be analyzed, meaning future updates might showcase slightly fluctuating efficacy metrics. AstraZeneca still plans to apply for emergency use authorization in the US in the coming weeks. Then, it'll be up to the FDA to authorize the vaccine.

Update, March 22, 2021: Results from a large US clinical trial involving more than 32,000 people and testing the AstraZeneca/Oxford COVID-19 vaccine candidate are finally available — and interim analysis relates that the vaccine showcased 79 percent efficacy in preventing symptomatic COVID-19 and 100 percent efficacy in preventing severe disease and hospitalization. This is higher than in past clinical trials in other areas of the world.

These results were based off of 141 symptomatic cases of COVID-19 from volunteers. The vaccine was administered to two-thirds of participants, and two doses were given four weeks apart. Results also showed that the vaccine efficacy rate in participants 65 years and older was 80 percent. AstraZeneca claims results were consistent "across ethnicity and age"; however, it's important to note that 79 percent of the volunteers in this trial identified as white, and only eight percent of volunteers were Black, four percent were Asian, four percent were Native American, and 22 percent identified as Hispanic.

Some European countries recently paused rollout of the vaccine due to reports of blood clots, but participants who received the vaccine in the trial had no increased risk of blood clots, according to The New York Times, and the independent data safety monitoring board assigned to reviewing the clinical trial data identified no safety concerns.

After the European Medicines Agency (EMA) stated on March 18 that the benefits of the AstraZeneca vaccine outweigh the risks and that there is no increase in the overall risk of blood clots, countries like France, Germany, Italy, and the Netherlands announced they would resume their rollouts. The EMA did note: "There have been very rare cases of unusual blood clots accompanied by low levels of blood platelets (components that help blood to clot) after vaccination. The reported cases were almost all in women under 55." More analysis by the EMA will continue.

Similarly to the newly authorized Johnson & Johnson vaccine, this shot is made from a weakened version of a common cold virus: an adenovirus. This particular adenovirus causes infections in chimpanzees, through which the genetic material of the SARS-CoV-2 virus spike protein is delivered. The body then makes copies of this protein, essentially training the immune system to defend against the COVID-19 virus.

This vaccine, too, can be stored at normal refrigerator temperatures for at least six months. AstraZeneca said it will continue to analyze the clinical trial data, and the company is preparing to apply for emergency use authorization in the US in the coming weeks. The vaccine is already authorized in more than 70 countries.

Update, Feb. 3, 2021: In addition to being 70.4 percent effective at preventing serious COVID-19, a new paper shows that the AstraZeneca/Oxford vaccine may also reduce transmission of the virus. Researchers tested for this by swabbing participants for the virus on a weekly basis, and found a 67 percent reduction in positive swabs among vaccinated people. The new research hasn't yet been peer-reviewed.

"We now know that the Oxford vaccine also reduces transmission and that will help us all get out of this pandemic," said Matt Hancock, the British health secretary, in an interview with the BBC. On Twitter, he called it "absolutely superb" news.

This is the first study to analyze whether any of the COVID-19 vaccines currently in use can prevent infection and transmission of the disease. The data we have so far on the Pfizer and Moderna vaccines only show that they can prevent serious illness, not that they prevent contraction of the virus in the first place, which is one of the reasons experts recommend we continue to wear face masks and practice social distancing even after we're vaccinated.

Update, Dec. 9, 2020: AstraZeneca announced in November that its COVID-19 vaccine developed with the University of Oxford had an average efficacy rate of 70.4 percent, and the analysis has since been peer-reviewed and published in The Lancet, confirming this efficacy. The analysis reiterated that the vaccine's effectiveness was 62 percent in trial participants in Brazil who received two full doses of the vaccine and 90 percent in those in the UK who received a half dose (or "low dose") followed by a full dose.

AstraZeneca originally did not disclose specifics on the 131 COVID-19 cases analyzed across the two trials when taking efficacy into account. The Lancet's analysis, though, noted there were 30 cases in people who were vaccinated and 101 in the control group.

The researchers wrote that the vaccine shows "significant vaccine efficacy of 70.4% after two doses and protection of 64.1% after at least one standard dose, against symptomatic disease, with no safety concerns." The safety data — stating "the vaccine had a good safety profile" — was collected from over 20,000 participants total enrolled across four clinical trials in those two locations and South Africa. Efficacy data from the trial in South Africa, where around 2,000 people are participating, was not included in this publication.

There were 175 "severe adverse events" in the trials: 84 events among those who received the vaccine and 91 in the control group, three of which were said to be possibly related to the vaccine itself or the control vaccine. This includes a case of haemolytic anaemia in a phase 1/2 UK control group, a potentially vaccine-related high fever in the South African trial, and one transverse myelitis case after vaccination.

Health officials have voiced concerns about the half-dose regimen given in the aforementioned UK trial, stating that the efficacy rate may go down after further testing (plus, the company's initial announcement didn't mention that this half-dose regimen resulted from an error). Additionally, the half dose was not tested in people over 55, and not all of the participants who received the initial half dose got the second full dose in the same time frame, according to The New York Times. "I think there remain questions about whether the result in the low-dose standard dose is a real robust biological result," Natalie Dean, a biostatistician at the University of Florida, told Stat News. "Will it hold up?"

Lack of transparency from AstraZeneca has affected its standing with the FDA, The New York Times reported, adding that it may take time before it catches up with companies like Moderna and Pfizer (note: Pfizer is on the verge of receiving emergency use authorization), especially given that the US clinical trial was delayed by 47 days due to transverse myelitis symptoms reported in two other participants. "Independent clinical review of these cases has indicated that one in the experimental group and one in the control group are unlikely to be related to study interventions, but a relationship remained possible in the third case," the analysis in The Lancet read.

As of now, the AstraZeneca clinical trial in the US continues. The New York Times reported that the trial was halfway to its enrollment goal of 30,000 people as of last week.

Original post, Nov. 23, 2020: In more COVID-19 vaccine news, a candidate developed by the University of Oxford and pharmaceutical company AstraZeneca was found to have an average efficacy rate of 70.4 percent following preliminary analysis of a phase 2/3 clinical trial in the UK and phase 3 trial in Brazil. This comes a week after Moderna initially announced its vaccine was 94.5 percent effective and Pfizer released updated info that its own vaccine has an efficacy rate of 95 percent.

The information from Oxford is derived from 131 total COVID-19 cases (out of 24,000 volunteers) and two separate dosing regimens. One showed a 90-percent efficacy rate when a half dose was given followed by a full dose at least one month apart, and another showed 62-percent efficacy rate when two full doses were administered at least one month apart, according to an AstraZeneca press release.

AstraZeneca said that an independent Data Safety Monitoring Board determined the vaccine showed protection from COVID-19 at least 14 days after receiving two doses. Oxford further said that a final analysis of the vaccine's efficacy rate is coming, as well as future review to determine how long the vaccine protects people from the virus. The companies are preparing for submission of this data around the world for early or conditional approval. "The Company will seek an Emergency Use Listing from the World Health Organization for an accelerated pathway to vaccine availability in low-income countries," AstraZeneca stated.

The vaccine is made from a weakened version of a common cold virus, adenovirus, and AstraZeneca reports that it contains the genetic material of the COVID-19 virus spike protein. "After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body," AstraZeneca said. Earlier trial results showed that the vaccine produced a strong antibody and T cell immune response across all ages, including older adults, according to Oxford.

The New York Times reports that it's not clear why the half-dose regimen has proven to be more effective, and though a clinical trial is also being conducted in the US, this specific half-dose regimen is not being tested yet, and AstraZeneca said it would work with the FDA to add it to that trial. Plus, The New York Times stated that results from the US trial are not expected until next year.

No serious safety risks were reported in the Brazil and UK trials, and there were no severe cases of COVID-19 or hospitalizations in the cases evaluated. This vaccine can reportedly be stored for up to six months in a regular refrigerator — by comparison, Pfizer's candidate needs to be stored at a freezing-cold temperature: minus 70 degrees Celsius. AstraZeneca said it's en route to making up to 3 billion doses in 2021, with 20 million doses available in the UK by the end of the year.

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