CDC study finds 9 out of 10 people in US got 2nd dose of COVID-19 vaccine

About nine out of 10 people in the U.S. who got the first shot of a coronavirus vaccine got the second in the two-dose series, according to a new study by the U.S. Centers for Disease Control and Prevention. Researchers and public health officials called the results "encouraging."

The findings are part of the first federal study to look at how many people are completing the series in the ongoing effort to stem the pandemic through vaccination. The study followed 12.5 million people and focused on the period between Dec. 14 to Feb. 14.

The researchers found 88% of individuals completed the series, and another 9% did not but still had time to complete the series within the six weeks that CDC officials recommend as the maximum span between doses. About 3% did not complete the series within six weeks, the study found.

"This is good news. We think these findings are really encouraging. The fact that most people are completing the two-dose series to be fully vaccinated shows the system’s working," said Robin Toblin of the CDC, one of the study’s authors.

The study did not explore why some people did not complete the series. CDC Director Dr. Rachelle Walensky also called the findings "very encouraging" and said "systems were in place" so that the 3% of missed doses in the study were not wasted.

"It is remarkable what we can do as a nation when we are united against the virus," Walensky said during a Monday media briefing.

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Researchers found completion rates varied across states and U.S. territories. It was as low as 75% in Utah and 79% in Puerto Rico, to as high as 95% in Michigan and 96% in West Virginia.

There may be different reasons for state differences, including winter weather that could have delayed vaccine deliveries and caused the cancellation of vaccination clinics, Toblin added.

The CDC says it is essential for everyone who receives a two-dose vaccine to get the second shot in order to receive its full protection. 

In total, more than 69.7 million people, or 21.0% of the U.S. population, have received at least one dose of a coronavirus vaccine to date, according to CDC data. Some 37.4 million people, or 11.3% of the population, have completed their vaccination.

The study concluded that public health officials "should identify and address possible barriers to completing the COVID-19 vaccination series to ensure equitable coverage across communities and maximum health benefits for recipients." The researchers recommended scheduling second-dose appointments during the first-dose administration and sending reminders about the second-dose visit.

Walensky also pleaded with Americans to continue following public health guidance on mask-wearing and refrain from nonessential travel as the coronavirus continues to infect more than 50,000 Americans each day. She cited escalating rates of travel, including around college spring break, as risks for another spike in virus cases. 

"This past Friday we saw more travelers past through our airports — over 1.3 million," Walensky said. "This is the most travelers that we’ve had over a single day since last March before the WHO declared the global pandemic. We have seen footage of people enjoying spring break festivities maskless. This is all in the context of still 50,000 cases per day."

Walensky noted that cases of the virus have been on a slight decline over the last several weeks, but remain at elevated levels. 

"We are just starting to turn a corner. The data are moving in the right direction, but where this goes is dependent on whether we all do what must be done to protect ourselves and others," she said.

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This story was reported from Cincinnati. The Associated Press contributed.