The U.S. will reach a new COVID-19 vaccination milestone Tuesday as it approaches 50% inoculation rate, a White House official confirmed to Fox News.

Half of all Americans will be fully vaccinated, meaning they either received two out of two doses for the Pfizer and Moderna vaccines or one single dose for the Johnson & Johnson vaccine as of Tuesday. 

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The majority of Americans (61.5%) have received at least the first dose, according to the Centers for Disease Control and Prevention (CDC).

The new milestone also comes as the country sees the fewest COVID-19 cases in 11 months and the fewest deaths since last summer. The seven-day average number of positive COVID-19 cases in the U.S. has dropped to 22,877, according to the CDC data as of May 23.

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The vaccines, authorized by the Food and Drug Administration, have proven to be highly effective in preventing COVID-19 cases and deaths with a 90% drop in infection risk, though some breakthrough cases have occurred in a fraction of vaccinated people, according to new data from the CDC.

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As of April 30, more than 10,000 breakthrough cases have been reported in 46 states and U.S. territories; among them, 6,446 (63%) of cases occurred in females and the median patient age was 58. More than one in four breakthrough infections were asymptomatic.

Nearly 1,000 (10%) of people with breakthrough infections were hospitalized, 29% of whom were asymptomatic or hospitalized for other reasons besides COVID-19, and 160 (2%) of whom died.