If you'll go near zombies, zombie horses, zombie villagers, husks, drowns, zombified piglins or zoglins depending on the distance away from them you'll get poison, slowness and hunger effect. each effect lasts for 3 seconds except hunger effect which lasts for 5 seconds.

Hunger effect = 5 blocks away

Slowness effect = 3 blocks away

Poison effect = half a block away