BERLIN (AP) — A new study estimates that at least 3.9 million unauthorized migrants — and possibly as many as 4.8 million — lived in Europe in 2017, with half of them in Germany and the United Kingdom.

The Pew Research Center said in a report released Wednesday the number of unauthorized immigrants grew from 2014, when about 3 to 3.7 million resided in Europe, and peaked in 2015-16 during the refugee crisis when some 1.3 million people arrived, mostly from war-torn countries like Syria, Iraq and Afghanistan. In 2016, an estimated 4.1 to 5.3 million people without residence permits lived in Europe.

Even with the growth of unauthorized migration to Europe, they accounted for less than 1 percent of Europe’s total population of more than 500 million in 2017.