stop strerilizing

My cousin continued till my niece was 18 months. Since my niece reached one year old, she decreased the frequency of sterilizing. She would wash the bottles with soap after every use, but would only soak them in hot water once every two days. Have another friend who stopped when baby was 8 months old. As she was trying to adjust baby to solid feedings, she ended up simply washing the bottles. Gradually, left out the sterilizing. From what she recalled, baby was fine and she didn't think her baby was weaker (didn't fall sick more frequently) then.