The AstraZeneca COVID-19 Vaccine Reduces Viral Transmission, New Study Shows
New research looking at the AstraZeneca COVID-19 vaccine suggests that it can prevent transmission of the virus in addition to the infection. Experts say this news is very encouraging—and may represent an important step on our way to coronavirus herd immunity.
The study, published as a preprint in The Lancet (meaning it has not been through the peer-review process), includes data from 17,177 participants in the U.K., Brazil, and South Africa over three months. The participants were randomized to receive either two doses of the vaccine or a placebo. There were 332 symptomatic COVID-19 cases in the study, 74 of which occurred in participants who received the first dose of the vaccine while 197 occurred in people who received a placebo. There were also no coronavirus-related hospitalizations after the first 21 days among those in the vaccine group, compared to 15 hospitalizations in the placebo group. Those findings led the researchers to conclude that the AstraZeneca COVID-19 vaccine, which was developed with Oxford University and has been authorized in the U.K. since late December, is 76% effective at preventing symptomatic infections.
But this study is unique in that it provides solid evidence that this vaccine can also reduce the spread of the virus even from people with asymptomatic infections. To examine this, the researchers took weekly nasal swab samples of all participants in the U.K. over the course of the study so that even if people did not have symptoms, the researchers would see if they tested positive for the virus. They found that a single dose of the vaccine reduced the number of positive nasal swabs by 67%, which suggests the vaccine “may have a substantial impact on transmission by reducing the number of infected individuals in the population.”
The two COVID-19 vaccines that are currently authorized in the U.S. are both mRNA vaccines, both of which are administered as two shots given a few weeks apart. They’ve both been shown to be at least 90% effective at preventing symptomatic COVID-19 infections, and experts think they are likely to also reduce transmission of the virus. But, as of right now, the AstraZeneca vaccine is the one for which there is the most evidence for that claim. The AstraZeneca vaccine was effective in this study for 12 weeks with a single dose, but the researchers here acknowledge that a second booster shot is “likely necessary for long-lasting protection.” Still, these results suggest that people can wait an extended period of time between those doses without losing too much of that protection, a strategy that may be necessary where the vaccine is in short supply.
“Another great result on COVID vaccine! AstraZeneca/Oxford vaccine resulted in 67% reduction in positive swabs (i.e., infection) among those vaccinated. Vaccine will reduce transmission,” Akiko Iwasaki, Ph.D., Waldemar Von Zedtwitz Professor of Immunobiology and Molecular, Cellular, and Developmental Biology at Yale University, wrote on Twitter.
“More terrific news,” Ashish K. Jha, M.D., MPH, dean of the Brown University School of Public Health, said on Twitter of the new results. “1. Vaccine appears to substantially reduce transmission. 2. Single dose protects against hospitalizations and deaths from COVID after vaccine has chance to work. 3. Waiting 12 weeks to give the 2nd dose is reasonable.”
Preventing infections is, of course, a huge deal and will help reduce the impact of the pandemic. But experts are hoping that, with enough people vaccinated, we’ll also get an extra level of protection through the concept of herd immunity, SELF explained previously. Generally, herd immunity is achieved when enough people within a certain community are immunized against a particular pathogen (typically through vaccination) so that even those who can’t or don’t want to get the vaccine get some protection. In order to get to that level of protection, we need vaccines that prevent both the symptoms of the infection as well as transmission.
It’s important to note, however, that this is different from the herd immunity strategy that some politicians pushed for earlier on in the pandemic, which proposed letting people get COVID-19 infections and the resulting immune response rather than following evidence-based prevention measures and achieving immunity via vaccines. Many public health experts agreed that this strategy would be extremely dangerous and would likely result in an overwhelming amount of coronavirus cases, hospitalizations, and deaths.
The AstraZeneca vaccine is still a ways from getting authorization from the Food and Drug Administration (after some issues early on in its clinical trials, the company may not be ready to submit all its data for authorization until the spring, the New York Times reported). And even with the vaccines we have available now, it’s crucial to keep up with the other public health tools we have that can slow the spread of the coronavirus. That includes wearing face masks, social distancing, hand washing, and avoiding crowds.
- What Is Herd Immunity, And Why Does It Matter?
- Dr. Fauci Says We Need at Least 75% of People to Get the COVID-19 Vaccine
- What Experts Think 2021 Will Look Like, Now That We Have Coronavirus Vaccines