The CDC says the Pfizer and Moderna COVID-19 vaccines, which both use mRNA technology, reduce the risk of coronavirus infection by 91% in fully vaccinated people, and about 81% in partially vaccinated people.
There are also findings to suggest vaccinated people are less likely to spread the coronavirus to others.
The results come from an ongoing study of almost 4,000 frontline workers, including health care workers, first responders, and other essential workers who are all more likely to be exposed to the coronavirus because of their occupations and how they interact with people.
The study participants have been taking weekly COVID-19 tests since mid-December, and if they have positive results, a lab tests the amount of viral load in their specimen. Researchers also check in with participants, how they are feeling and when they received their vaccinations.
The term “fully vaccinated” refers to anyone who is two weeks or more after their second Pfizer or Moderna vaccine dose. This study did not include the Johnson & Johnson single shot COVID-19 vaccine, which received FDA approval for emergency use earlier this year after the two mRNA versions of the vaccine.
The reduction in infections applied to those with symptoms and those without.
Researchers with the Centers for Disease Control and Prevention also looked at how serious those symptoms were for those who contracted COVID-19 while vaccinated.
They found those participants who were fully or partially vaccinated were more likely to have milder and shorter illnesses compared to those who contracted COVID-19 who were not vaccinated.
“For example, fully or partially vaccinated people who developed COVID-19 spent on average six fewer total days sick and two fewer days sick in bed. They also had about a 60 percent lower risk of developing symptoms, like fever or chills, compared to those who were unvaccinated,” the study found.
Some study participants did not develop symptoms at all.
When scientists looked at the viral load of those who contracted COVID-19, they found those who were fully or partially vaccinated had 40% less detectable virus in their nose than those who were not vaccinated.
Those who were fully or partially vaccinated also had detectable levels of the coronavirus in their samples for six fewer days than those who were not vaccinated.