The original whooping cough vaccine that was phased out in the 1990s for safety reasons was more effective for kids than the new vaccine, a new study found.

An outbreak in California from 2010 to 2011 was triggered by the new vaccine, which caused six times as many cases of whopping cough, also called pertussis, than was seen with the old vaccine.

And in 2012, the country incurred more than 41,000 infections and 18 deaths (mainly infants), the most cases since the late 1950s, according to the Centers for Disease Control and Prevention (CDC).

"This is an ongoing saga," Dr. H. Cody Meissner, chief of the infectious diseases division and associate director of the clinical microbiology laboratory at Tufts University School of Medicine, told Reuters.

Recent increases in cases of whooping cough are creating concern "about losing control of pertussis in the United States."

The study, conducted by investigators in the Kaiser Permanente Northern California health system, looked through the medical histories of 138 teens and preteens who had whooping cough and compared them to 55,000 who did not test positive for whooping cough during the California outbreak.

They found that 78 per 100,000 teens were infected every year from 2010 to 2011, and most of the kids were administered the new acellular vaccine as their fifth dose.

As a baby, the CDC recommends parents give their children four doses of diphtheria, tetanus and pertussis vaccine, or DTaP, between the ages two and 18 months old. The fifth is given when they're between four and six, while a booster could be taken when their 11 or 12 years old.

The older vaccine was used since the 1940s and included the whole pertussis bacteria, which explained the increase in crying and fever, among other side effects, in babies. That was when a newer, safer version arrived in the 1990s.

"But the price we've paid to get more safety is that we have less effectiveness," Meissner told Reuters. "It doesn't protect as well against pertussis."

Specifically, those kids who were given the acellular version for their first four doses increased their risk of contracting whooping cough by 40 percent.

Researchers are now focusing on creating a third version that would take into account the safety and effectiveness.

"Right now, make sure your children receive all their vaccines and boosters on schedule," Dr. Nicola Klein, co-director of the Kaiser's Vaccine Study Center, told HealthDay. "This [acellular] vaccine does work, just not for as long as we would've hoped."

The study was published online May 20 in the journal Pediatrics.

Source: Klein NP, Bartlett J, Fireman B, et al. Comparative effectiveness of Acellular versus whole-cell pertussis vaccines in teenagers. Pediatrics. 2013.