Story at a glance
- A study from the CDC reports the first dose of Pfizer or Moderna vaccines is about 80 percent effective.
- The second dose pushes effectiveness up to 90 percent.
- The experts recommend people to get both doses.
A recent study published by the Centers for Disease Control and Prevention (CDC) reports results from Pfizer and Moderna mRNA vaccinations. The study followed nearly 4,000 people who were given either the Pfizer or Moderna vaccines from Dec. 13, 2020 through March 13, 2021. The participants included health care personnel, first responders and essential workers who were tested weekly for SARS-CoV-2, the coronavirus causing COVID-19.
The researchers recruited people from eight locations around the U.S. During the study period, they detected 161 infections, and any that were detected during the first 13 days after the first dose were not included in the analysis.
The team found that about two weeks after the second dose the vaccines were 90 percent effective against SARS-CoV-2 infections, regardless of symptom status. This means that the vaccinated people were 90 percent less likely to get infected. The report also states that two weeks after the first dose, but prior to receiving the second dose, effectiveness was about 80 percent.
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“These findings indicate that authorized mRNA COVID-19 vaccines are effective for preventing SARS-CoV-2 infection, regardless of symptom status, among working-age adults in real-world conditions,” the researchers wrote in the study. “COVID-19 vaccination is recommended for all eligible persons.”
The second dose is important for inducing long-term immunity in the body.
“The reason that they are two-dose vaccines is that the second doses give you a titer of neutralizing antibodies, virus-specific neutralizing antibodies that is almost 10 growth fold greater than after the first dose,” Paul Offit, a voting member of the FDA’s Vaccines and Related Biological Products Advisory Committee who reviewed both Pfizer’s and Moderna’s vaccine for emergency use authorization, told CNBC.
The CDC study focused on people who were working in real-life conditions to further support the findings from the clinical trials.
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“There was no guarantee that the vaccines were going to perform the same in the real world, where there were a lot of concerns about freezers and temperatures,” said Mark Thompson, a CDC epidemiologist and lead author of the report, to The Washington Post.
Some studies are focusing on the effectiveness of one dose in other settings, such as care homes. In the U.K., researchers found that one dose of the Pfizer or AstraZeneca vaccines was 62 percent effective at preventing infections in care homes.
“Our findings show that a single dose has an effect that persists from four weeks to at least seven weeks after vaccination,” said Laura Shallcross, who is a public health medicine consultant at the Institute of Health Informatics at University College London, to the BBC. “We can also infer that the vaccines protect against the highly transmissible UK variant, as this was prevalent during the study period.”
The CDC study provides important information about how the vaccines are working to prevent infection in groups of people who are at greater risk during a time when cases are high and new variants of the coronavirus are spreading. The experts recommend that people get both doses of the vaccine, but it may give some peace of mind that a single dose also provides a good amount of protection.
“What we really want to do is test these vaccines in the real world, to see how well they work,” said Monica Gandhi, an infectious diseases expert at the University of California at San Francisco who was not involved with the study, to the Post. “It’s really incredible news for how safe you can feel after vaccination.”
For up-to-date information about COVID-19, check the websites of the Centers for Disease Control and Prevention and the World Health Organization. For updated global case counts, check this page maintained by Johns Hopkins University.
You can follow Chia-Yi Hou on Twitter.
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