AstraZeneca Plc's COVID-19 vaccine demonstrated 74 percent efficacy at preventing symptomatic disease, a figure that increased to 83.5 percent in people aged 65 and older, according to long-awaited results of the company's US clinical trial published on Wednesday.
Overall efficacy of 74 percent was lower than the interim 79 percent figure reported by the British drugmaker in March, a result AstraZeneca revised days later to 76 percent after a rare public rebuke from health officials that the figure was based on "outdated information."
The data looked at more than 26,000 volunteers in the United States, Chile and Peru, who received two doses of the vaccine spaced about a month apart. The results were published in the New England Journal of Medicine.
There were no cases of severe or critical symptomatic COVID-19 among the more than 17,600 participants who got the vaccine, compared with 8 such cases among the 8,500 volunteers who got the placebo. There were also two deaths in the placebo group but none among those who received the vaccine.
"I was pleasantly surprised," Dr. Anna Durbin, a vaccine researcher at Johns Hopkins University and one of the study's investigators, said of the overall result. "It was also highly protective against severe disease and hospitalization," she said.
Frequently Asked Questions
A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.
There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.
Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.
There were no cases of a rare but serious blood clotting side effect called thrombosis with thrombocytopenia that has been linked to the AstraZeneca vaccine developed with Oxford University researchers.
AstraZeneca said in late July it planned to file for full approval with the US Food and Drug Administration, rather than seek emergency use authorization. Chief Executive Pascal Soriot told a media briefing at the time he hoped the vaccine could still play a role in the United States, even though the process was taking longer than expected.
The company is exploring booster doses for people who have already been vaccinated with two doses of either its own shot or mRNA-based vaccines from Pfizer/BioNTech, or Moderna.
The vaccine, known as Vaxzevria, is authorized for use in more than 170 countries. A spokesperson said the company expects to file for US approval later this year.Durbin said she does not expect Vaxzevria to be used much in the United States, but securing FDA approval "does give them gravitas."