How Effective Is AstraZeneca’s COVID-19 Vaccine? Here’s What Experts Know so Far
The COVID-19 vaccine developed by AstraZeneca and Oxford University has been approved for emergency use in Europe, Mexico, and India.
The vaccine has been proven to be effective against common strains of the novel coronavirus, but seems to offer little protection from the South African variant; the country has now stopped offering this vaccine to its citizens.
It’s unclear when the AstraZeneca vaccine could gain approval from the FDA.
A vaccine created by the University of Oxford and biopharmaceutical company AstraZeneca can protect people from developing a serious form of COVID-19 and slow the transmission of the virus, according to new research. While previous vaccines have shown they help reduce the risk of serious complications from the novel coronavirus, this is the first to suggest that it can actually reduce person-to-person spread.
However, a separate trial found that AstraZeneca’s vaccine offers only minimal protection against the highly infectious coronavirus variant that has emerged from South Africa, failing to meet the threshold for emergency use. Those results have led South Africa to completely halt distribution of the AstraZeneca vaccine.
Although more research is necessary before drawing final conclusions from either of these studies, the outcome is clear: We’re playing catchup with the virus, which continues to mutate across the globe. Here’s what experts know about the Oxford-AstraZeneca vaccine so far.
How Does the Oxford-AstraZeneca COVID-19 vaccine work?
The AstraZeneca vaccine uses a modified version of a chimpanzee adenovirus, which is a common cold virus that has been altered with a gene from the novel coronavirus’ spike protein (the portion of the virus that latches onto human cells and triggers an immune response). Once you’re vaccinated, the modified virus can enter your cells but can’t replicate inside them—meaning it won’t make you sick.
Then, the modified adenovirus is pulled into your body’s cells and gives your cells messenger RNA (mRNA), which tells them to start making spike proteins. As a result, your body creates antibodies designed to attack SARS-CoV-2, the coronavirus that causes COVID-19. If your body encounters the coronavirus in the future, it will be better prepared to respond and fight it off more efficiently.
Compared to Pfizer’s and Moderna’s mRNA vaccines, the Oxford-AstraZeneca vaccine is a “step earlier in the process” of making antibodies against SARS-CoV-2, says William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine. “With this vaccine, we get the DNA and it initiates in our body the mRNA that creates the message for us to make the spike protein,” he explains. “It’s similar, but a step ahead.”
How effective is the Oxford-AstraZeneca COVID-19 vaccine?
The first study, which was published in Preprints with The Lancet on Feb. 1, analyzed data from participants in the U.K., Brazil, and South Africa. The researchers found that a single dose of the vaccine is 76% effective at preventing severe forms of COVID-19 from 22 to 90 days after someone has been vaccinated.
However, timing seems to matter with the second dose. Researchers found that the vaccine’s overall efficacy began at 54.9% when the doses were given within less than six weeks. However, when people are given a second dose spaced 12 or more weeks apart from the first—much longer than the month currently being recommended—the efficacy rises to 82.4%. (For comparison, the annual flu shot is usually between 40 and 60% effective.)
“Potentially, the first dose of the vaccine gives a lot of protection, but you’re going to need the second dose to get good, durable protection,” says John Sellick, D.O., an infectious disease expert and professor of medicine at the University at Buffalo/SUNY in New York. This isn’t rare for vaccines, though, he says: The hepatitis A vaccine and many childhood vaccines also require two shots for this reason.
One of the most noteworthy aspects of this vaccine is that data has shown it may help tamp down the spread of the current dominant strain of the coronavirus. The researchers took nasal swabs from trial volunteers in the U.K. and found there was a 67% reduction in swabs that were positive for the virus after people were vaccinated.
“We’re going to need epidemiological studies to show that transmission is actually reduced [with the AstraZeneca vaccine],” Dr. Sellick explains. “But it’s helpful to see that you’ll decrease the amount of virus that’s actually shed.”
But that promising news has been dulled by the results of a new trial conducted by researchers at the University of the Witwatersrand in Johannesburg. The study, which followed about 2,000 South African residents, found less than 25% efficacy against mild and moderate illness caused by the South African variant of COVID-19, failing to reach the international threshold for emergency vaccine approval.
South Africa’s dominant strain, known as B.1.351, is more contagious than previous variants and causes most of the COVID-19 infections in the country. Now, South Africa has halted all vaccinations using the AstraZeneca vaccine only days after receiving a million doses from the company, a major blow to the country’s—and the globe’s—immunization efforts. The variant has been detected in the U.S.
“These results are very much a reality check,” Shabir Madhi, Ph.D., a virologist at the University of the Witwatersrand who led the trial, said at a press conference this week. Further research is needed to determine if the vaccine prevents severe illness, hospitalizations, and deaths for those infected with B.1.351. If it does, this news won’t be as disheartening as it appears.
What are the side effects of the Oxford-AstraZeneca COVID-19 vaccine?
Like the Pfizer and Moderna vaccines, AstraZeneca says you might experience mild, cold- or flu-like symptoms after being vaccinated, including:
Temporary injection site pain and tenderness
Mild-to-moderate headache
Fatigue
Chills
Fever
General discomfort
Muscle aches
Remember, experiencing side effects after getting any vaccine is totally normal and expected, as it’s a sign that your body is setting off an immune response.
How is the Oxford-AstraZeneca COVID-19 vaccine stored?
The vaccine can be stored, handled, and transported at normal refrigerator temperatures for at least six months and be given in normal healthcare settings, like a doctor’s office. Experts say this is a huge plus. “It will enhance its capacity to be delivered and administered around the world,” Dr. Schaffner says.
This is a big advantage against its current counterparts, as mRNA is particularly fragile and needs to be stored in speciality freezers. Pfizer’s vaccine is especially tricky, as it must be stored at -94°F to remain stable and effective. Moderna’s vaccine, meanwhile, should be stored at -4°F.
When will the Oxford-AstraZeneca COVID-19 be authorized for use in the U.S.?
The vaccine has been authorized for use by the European Union and is being administered in the U.K., as well as India and Mexico as of press time. However, AstraZeneca hasn’t released data from its phase 3 clinical trial in the U.S. or submitted it to the Food and Drug Administration yet. The New York Times reports that AstraZeneca should have enough safety data gathered to seek authorization in March at the earliest, and that the federal government has agreed to buy 300 million doses once the vaccine gets the green light.
“It’s going to be some time before Americans have access to this vaccine, because it hasn’t gone through the FDA process yet,” says infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security. “But it will probably end up immunizing a lot of people around the world.”
This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.
Go here to join Prevention Premium (our best value, all-access plan), subscribe to the magazine, or get digital-only access.
FOLLOW PREVENTION ON INSTAGRAM
You Might Also Like
