Let us go back to 2011 in New York where we saw a rare outbreak of measles occur, however, what was interesting about this particular outbreak is that many of those contracting the virus
‘A person fully vaccinated against measles has contracted the disease and passed it on to others. The startling case study contradicts received wisdom about the vaccine and suggests that a recent swell of measles outbreaks in developed nations could mean more illnesses even among the vaccinated’. [source]
This began to raise questions in the science community about the effectiveness of the MMR vaccine, a study by The Oxford Academic Clinical Infectious Diseases concluded that:
‘The clinical presentation and laboratory data of the index patient were typical of measles in a naive individual. Secondary patients had robust anamnestic antibody responses. No tertiary cases occurred despite numerous contacts. This outbreak underscores the need for thorough epidemiologic and laboratory investigation of suspected cases of measles regardless of vaccination status.’ [source]
So, as the case in New York back in 2011 clearly shows, being vaccinated against measles does not prevent an outbreak in a community occurring, in fact being vaccinated twice may not even prevent an individual from contracting the virus and spreading it further.
What we must understand here is the implications of a vaccinated community believing they are immune to viruses such as Measles and thus not taking the necessary precautions when a virus outbreak does occur.
An individual who is unvaccinated is far more likely to take the responsible precautions necessary to avoid spreading the virus further.