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First 'real-world' study on Pfizer and Moderna COVID-19 vaccines found 90% efficacy

The CDC director called the results "tremendously encouraging."
/ Source: NBC News

The Pfizer and Moderna COVID-19 vaccines are extremely effective in the real world, reducing infections by 90% in fully vaccinated people, the Centers for Disease Control and Prevention reported Monday.

CDC Director Dr. Rochelle Walensky called the study "tremendously encouraging" in a briefing Monday, adding that it "underscored the importance of getting both of the recommended doses of the vaccine in order to get the greatest level of protection against COVID-19, especially as our concerns about variants escalate."

The findings are the first real-world data from the United States, and are in line with similar research from other countries. A study from Israel recently found the Pfizer vaccine to be 97% effective in preventing COVID-19, including severe disease and death.

The CDC study included 3,950 people in the U.S. who received either the Pfizer-BioNTech or Moderna vaccine during the height of country's winter surge, from mid-December to mid-March. All were essential workers, including health care personnel and first responders from six states: Arizona, Florida, Minnesota, Oregon, Texas and Utah.

Two weeks after participants received both of the recommended doses, their risk of SARS-CoV-2 infection was reduced by 90%. (People are considered fully vaccinated two weeks after they received their final dose.)

Even the first dose had an effect, reducing infection risk by 80%, the study found.

Importantly, the research also showed that both vaccines not only prevent people from getting sick with COVID-19, they also help prevent asymptomatic infections, in which people never develop symptoms.

Public health officials view COVID-19 vaccines as the best way to end the worst of the pandemic, particularly as a growing number of states relax restrictions and lift mask mandates.

Just over 140 million people in the U.S. have received at least one dose of either the Pfizer or the Moderna vaccine, and an additional 3 million have had the one-dose Johnson & Johnson vaccine. More than 51 million Americans have been fully vaccinated.

But that leaves many Americans still vulnerable to COVID-19, and Walensky issued an urgent warning Monday as cases are once again on the rise. The average number of daily COVID-19 cases is just under 60,000 — a 10% increase from the previous week. The numbers of hospitalizations and deaths have also risen in recent weeks, but not as dramatically.

This story was originally published on NBC News.