Life expectancy in the US declined by about a year and a half in 2020, the largest annual decline since World War II, and the COVID-19 pandemic is largely to blame, the Centers for Disease Control and Prevention (CDC) said Wednesday.

For the total population, life expectancy — generally a reliable measure of a nation's health, based on mortality in a given year — declined from 78.8 years in 2019 to 77.3 years in 2020; COVID-19 contributed to 74 percent of the decline, according to data released by the CDC.

"Life expectancy has been increasing gradually every year for the past several decades," Elizabeth Arias, a CDC researcher who worked on the report, told Reuters. "The decline between 2019 and 2020 was so large that it took us back to the levels we were in 2003. Sort of like we lost a decade.''

The report also reflects the disproportionate impact of COVID-19 on racial, gender and ethnic groups.

Latinos, who have a longer life expectancy than non-Hispanic black or white people, saw a decline of three years, from 81.8 years in 2019 to 78.8 years in 2020, which is the biggest decline among racial groups.

Black Americans lost 2.9 years of life expectancy, from 74.7 years in 2019 to 71.8 in 2020. There was a decrease of 1.2 years among white people. The report didn't include data for Asian Americans or other racial groups.

COVID-19 was responsible for 90 percent of the decline in life expectancy for the Hispanic population. For the black population, which saw life expectancy reach its lowest level since 2000, COVID-19 contributed to 59 percent of the decline. For the white population, which saw life expectancy reach the lowest level since 2002, COVID-19 contributed to 68 percent of the decline.

"We were sounding the alarm early on, and I think (the data) reflects directly the longstanding structural racism in this country and how that disproportionately impacts black and Hispanic communities. It impacts where they live, work, and play and ultimately impacted the risk of dying from COVID-19," Chantel Martin, an assistant professor of epidemiology at the Gillings School of Global Public Health at the University of North Carolina, Chapel Hill, told USA Today.

Disparities in life expectancy between men and women also widened in 2020, with women now expected to live 80.2 years, or 5.7 years longer than men — six months more than expected in 2019.

Life expectancy won't recover to pre-pandemic levels in 2021 and could decline again if a new COVID-19 variant emerges that vaccines don't protect against, Arias and other population-health experts told The Wall Street Journal.

An increase in drug overdose deaths was also a factor in declining life expectancy. The CDC's National Center for Health Statistics (NCHS) last week released interim data showing that US drug overdose deaths rose nearly 30 percent in 2020, and more than 93,000 people died from overdoses in 2020, the highest number reported in a single year.

According to the NCHS, an estimated 11 percent of the decline in life expectancy is due to increases in deaths from accidents and unintentional injuries, and more than one-third of all unintentional injury deaths were drug overdoses.

Other contributing causes of death include homicide, diabetes and chronic liver disease and cirrhosis, the report noted.

Since the middle of the 20th century, life expectancy has steadily climbed in the US, with some small decreases in recent years.

But a small increase was recorded in 2018, when it improved from 78.6 to 78.7 years, which was the first time since 2014 that the number had gone up. In 2019, the number also increased by a small increment, the CDC reported.

According to the data from the United Nations Population Division, in 2020, life expectancy in the US ranked 46th worldwide, below most other high-income countries.