+ isn't the "official" concatenation operator, and indeed it doesn't always
work properly. E.g. the following code fails

Private Sub CommandButton1_Click()
Dim a As Integer: a = 111
Dim b As Integer: b = 222
Dim c As String: c = a + b + "another string"
Range("a1").Value = c
End Sub

The error  is a type mismatch on the c = a + b + "another string"

However, ampersands work  fine:

Private Sub CommandButton1_Click()
Dim a As Integer: a = 111
Dim b As Integer: b = 222
Dim c As String: c = a & b & "another string"
Range("a1").Value = c
End Sub

sets A1 to 111222another string  as you'd expect.