If *fullwhack* (albeit nice!) seems a bit extreme to you but you still want to adhere to the colloquial undertone...
Multiple vaccines, one inoculation.

If you choose to have your baby vaccinated with the combination diphtheria, tetanus, whooping cough (pertussis), polio and Haemophilus influenzae type 2 vaccine, a *mega-jab* collectively known as the DTap-IPV-Hib, your child may be at an increased risk of having a vaccine-induced seizure.
http://www.naturalnews.com/035072_Dtap_vaccine_seizures_babi...

The *mega-jab*:
A radical approach to immunisation is to inject raw DNA directly into patients. Tests are already under way to induce immunity to a range of infections. DNA vaccines could immunise people against a range of infections simultaneously with just one jab.
http://www.independent.co.uk/news/science/23-ways-that-dna-c...

Wow, that's a *mega-jab*!! How big was the needle?? hehehe ... And polio here is the oral live vaccine, not the inactivated one. And of course the NHS is still very ...
http://forums.ivillage.co.uk/t5/General-Discussions/Six-in-o...

Could it be that child's genetic predisposition to react with all those vaccines put together in one *mega-shot*?
http://hotair.com/headlines/archives/2012/08/23/trump-inocul...

The MMR decision just came about because its a *mega shot*.
http://www.rachelshumor.com/2009_03_01_archive.html