A sharp and steady decline in the birthrate since the Great Recession means births are no longer such a powerful driver of growth. Immigration, which would typically pick up the slack, is down sharply too. And deaths are rising as baby boomers age and drug overdoses surge. Now there is the added threat of the coronavirus, which is particularly lethal for older people.

Births fell to 3.79 million in the year ending in July 2019, while deaths jumped to 2.83 million. That difference — the natural growth of the population — is now less than 1 million for the first time in decades. When combined with immigration, which fell to a net gain of 595,348 people — down by nearly half since 2016 — the United States had a population increase of just 0.48 percent.

That is the lowest rate since the last time the country was in the midst of a severe pandemic — the flu that killed hundreds of thousands of Americans between 1918 and 1919.

William Frey, chief demographer at the Brookings Institution, said the numbers put the last decade on track to be the slowest 10-year period for population growth since the government started counting in 1790.

The balance of births and deaths is critical to a country’s demographic health. If deaths start to outnumber births — and immigration does not make up the difference — society can strain under the weight of a growing retiree population with too few working-age people to support it. Deaths exceed births in several European countries, including Italy, Greece, Germany and Spain. In some, immigration keeps the populations growing.