A new study suggests that the messenger RNA COVID-19 vaccines from Moderna and Pfizer-BioNTech are about 90% effective in preventing COVID-19 in the real world.

  • That 90% number is for full vaccination. One dose appears to be 80% effective, according to the study, which was published by the Centers for Disease Control and Prevention.
  • “This is very reassuring news,” said the CDC’s Mark Thompson, the study’s lead author, according to The Associated Press. “We have a vaccine that’s working very well.”

What did the new COVID-19 vaccine study say?

The study — released in the Morbidity and Mortality Weekly Report — reviewed the case files for about 4,000 health care workers, first responders and other essential workers to see if they got infected with COVID-19 after getting fully vaccinated.

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  • The participants received COVID-19 tests every week to see if they were infected — with or without symptoms, according to The Associated Press.

How effective is Moderna or Pfizer after one or two doses?

  • Vaccine effectiveness proved to be 90% after two doses — slightly less than the 94% to 95% reported in the Pfizer and Moderna clinical trials.
  • One dose of the vaccines proved to be 80% effective at stopping infection after two weeks.
  • “That estimate, however, only applies to the brief period until the second dose was administered. The study was not designed to test how well the vaccine works if an individual does not receive the second dose,” according to STAT News.

So do you get COVID-19 symptoms?

  • The study found that 42% of the positive COVID-19 infections came from patients who were tested after developing symptoms. About 10.7% of those who tested positive for COVID-19 had no COVID-19-related symptoms, per STAT News.
  • There were no deaths from COVID-19 in the study.
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Why the new COVID vaccine study matters

CDC Director Dr. Rochelle Walensky said in a statement (via The Associated Press): “These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead.”