Because of evolution. Watch this post become representative of the user base with its up/downvoats.

Obviously its the fault of the 1% of people who chose not to vaccinate

/s (the unvaccinated are probably the wealthy elite with stock in the vaccine pharmaceuticals)

I understand that this is the conspiracy subverse but there are reasonable explanations for this stated in the study that the article sources.

The study that the article quotes states that the dosage of the vaccine was not adequate. That they found that "A timely two-dose MMR vaccination schedule is recommended, with the first dose at 8 months and the second dose at 18–24 months. An MR vaccination speed-up campaign may be necessary for elder adolescents and young adults, particularly young females."

Also Zhejiang province has a population of 55 million by 2013 statistics, if 99.5% are vaccinated the amount of people unvaccinated and vulnerable would be about 275,000 people. because of the large amount of people still unvaccinated there is considerable amounts of people that can be infected and become viral reservoirs that could give rise to different stains that could infect vaccinated population. This is the basis of herd immunity.

Damn Chinese and their counterfeit vaccines..