From previous post ( WEREWOLF : NOT ENOUGH TO AVOID VAMPIRISM ), here are some cons about that problem explained below :
1 - If you are traveling on a horse or walking from place to place, you may be suddenly attacked by vampires and they will spell on you so you will get vampirism.
2 - If you want to avoid the above fact, you need to fast travel from place to place, nevertheless, when you show up at your new destination, you may be attacked by vampires and if so, they will spell on you and you will get vampirism. This happened to me twice while fast traveling to two different houses.
3 - If you are either fast traveling or not, I do recommend : save your game before doing it, sneak before you fast travel so when you show up in your new location, and vampires are waiting for you, they will probably won't see you and will give you time to prepare for combat and avoid being hit by their spells. If you do not have a very good sneak perk or an enchanted item that allow you to sneak properly, you are dammed.
4 - You are practically not free anymore to travel as you did before so penalty of being infected with vampirism. You must be watching your back all the time and this is not right. If a dragon attack you, you won't get killed instantly, you will have time to react but if you are attacked by a vampire spell, you a simply stuck to vampirism even if you are a werewolf while in human form. Not good !
5 - You need to save a lot and probably reload your game again if you get hit by the vampire spell while traveling. This is time consuming and probably your system will freeze as it did happened to me twice already.
6 - You can not have Serana with you anymore because you might get hit by her vampire spell and get vampirism anyway. I got vampirism from her several times so I had to reload and start all over again.
7 - Instead you being looking for vampires to kill them, they can show up unexpectedly and spell on you so you will get vampirism.
8 - Once infected, there is not cure unless you reload your game and start all over again. If you don't do that, you will become a vampire even though you are a werewolf. How so ? Try it and you will see.
9 - If you travel as a beast ( werewolf ), you may be attacked by anyone on sight and you are not powerful enough to deal with several enemies at the same time especially if they are vampires and necromancers. Also, as a werewolf you do not have the capability to stay on beast form during 24 hours, and even if you could, that will negate your real nature of being primarily a dragonborn not a werewolf.
As you can see, this is a problem I believe Bethesda should fix ASAP, otherwise, you are playing defensively all the time and unprotected even if you are a werewolf. I have not idea why they overlooked this. It does seems like they do not have a quality team to test the game and all its details so they could be fixed before giving us the choice to play it. Now the only option for them is either to patch it or leave it as it is. If they patch it, when will that happen ? If not, we are stuck to the above facts. Not good !