UNICEF is urging mothers to do more to start breastfeeding their newborns within an hour of birth, saying breast milk is a baby's "first vaccine."

The U.N. children's agency says some 77 million newborns — or about 1 in 2 — don't get breastfed within the first hour after birth, depriving them of key nutrients, antibodies and skin-to-skin contact.

UNICEF said Friday that newborns account for nearly half of all deaths of children under 5 years old, and getting more newborns breastfed exclusively in the first six months of life could save over 800,000 lives each year.

World Health Organization spokeswoman Fadela Chaib took aim at some claims that infant formula has the same benefits as breast milk, saying "it's a lie. It's not the same."