The Orphan Collector by Ellen Marie Wiseman

 One of many novels that will likely draw comparisons between the 1918 flu epidemic and the recent Covid epidemic.  Pia is a 13 yr. old German immigrant.  Her father goes to fight in WWI and her mother dies of the flu.  To try and find food for her infant twin brothers, she places them for safety in a cubby behind a bedroom wall and looks for help.  First stop is the apartment of Finn, an Irish immigrant who is her best friend.  When no one answers the door, she suspects the worse and heads out to the ravaged city of Philadelphia.  While searching, she falls victim to the flu that can strike and kill in minutes.  Six days later she awakes with no idea what has happened to her brothers.  She is driven by her hope that they survived and her need to find them.
Beatrice Groves lives in the same apartment building as Pia.  She is grief stricken by the death of her infant son.  This, mixed with her hatred of the crowds of immigrants entering the country, drives her to unthinkable acts of selfishness and cruelty.  And so their stories begin to intertwine.  There is so much depressing detail - rotting bodies, cruel orphanages, the orphan train, separated families - it was hard to believe there could possibly have been a happy ending.