I'm checking the WMI for about 10 thousand PCs. WMI works with Avast for all 32 bit products, but doesn't work for 64 bit products.
I'm doing it in C but the visual basic equivalent is
Set objSWbemServices = GetObject("winmgmts:\\.\root\SecurityCenter")
Set colFirewall = objSWbemServices.ExecQuery("Select * From antivirusProduct",,48)
For Each objAntiVirusProduct In colFirewall
WScript.Echo( objAntiVirusProduct.displayname & " " & objAntiVirusProduct.productUptoDate)
Next
Note, however, Microsoft security center for Win64 fully detects Avast on Win64. Do you have to do something to get the 64 bit WMI to work?