We've had several cases of whooping cough show up in our school district in past month. Pertussis was never completed eliminated like other illnesses such as mumps, measles, etc. pretty much were. The pertussis vaccine was changed about 1990 due to side effect problems, and unfortunately the current vaccine is not quite as effective as the original vaccine type was. The new one appears to start losing effectiveness as children get older, so whooping cough can still be an issue.

From the CDC:

"Since the early 1980s, there has been an overall trend of an increase in reported pertussis cases. Pertussis is naturally cyclic in nature, with peaks in disease every 3-5 years. But for the past 20-30 years, we've seen the peaks getting higher and overall case counts going up. There are several reasons that help explain why we're seeing more cases as of late. These include: increased awareness, improved diagnostic tests, better reporting, more circulation of the bacteria, and waning immunity.
When it comes to waning immunity, it seems that the acellular pertussis vaccine (DTaP) we use now may not protect for as long as the whole cell vaccine (DTP) we used to use. Throughout the 1990s, the US switched from using DTP to using DTaP for infants and children. Whole cell vaccines are associated with higher rates of minor and transient side effects such as fever and pain and swelling at the injection side. Rare but serious neurologic adverse reactions including chronic neurological problems rarely occurred among children who had recently received whole cell vaccines. While studies have had inconsistent results that the vaccine could cause chronic neurological problems, public concern in the US and other countries led to a concerted effort to develop a vaccine with improved safety. Due to these concerns, along with the availability of a safe and effective acellular vaccine, the US switched to acellular vaccines."