Are heartworm vaccine injections preferable to pills?

I read somewhere thats it dangerous in that it might cause anaphylactic reaction etc. Do you prevent heartworms in your dogs by pills or jabs?
Update: @uhave2bekiddingme: Its a sheltie. does that applies to shelties too? they have similarities with collie.
Update 2: @ugot2bekiddingme: oh i see u meant other herding breeds as well. =|
Update 3: After macthyme’s respone i feel quite silly asking this qns lol. I did some reading but am still quite ignorant about e subject. I mean if jabs are supposedly better than pills, I would rather have my dog do jabs even though they probably prefer pills better.
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