Pertussis Has Been Making a Big Comeback in the Last

Pertussis has been making a big comeback in the last few years, after being on the decline for quite a long time. Why is this?

A) Few people have ever received pertussis vaccines because there have been links to autism.
B) The strain of Bordetella pertussis that is now the major cause of pertussis is much more virulent than earlier strains.
C) The pertussis vaccine does not seem to protect for a lifetime, so those who received the vaccine as kids may become susceptible in adulthood.
D) People eat so much refined sugars and starches that our immune systems are much weaker, thereby not being able to adequately protect against pertussis bacteria.