HealthDay News — Adolescents who were given whole-cell pertussis vaccines in childhood were better protected in a recent outbreak than those given acellular pertussis vaccines, researchers found.
During the 2010-2011 California pertussis outbreak, teens whose first four diphtheria-tetanus-pertussis shots contained whole-cell pertussis (DTwP) were six times less likely to be pertussis PCR-positive than those whose shots contained acellular pertussis (DTaP), Nicola P. Klein, MD, PhD, from the Northern California Kaiser Permanente Vaccine Study Center in Oakland, and colleagues reported in Pediatrics.
“Teenagers who received DTwP vaccines in childhood were more protected during a pertussis outbreak than were those who received DTaP vaccines,” they wrote.
Children vaccinated with DTaP were also four times more likely to get the disease than peers who were vaccinated with a mixture of both DTaP and DTwP, results from the large case-control study indicated.
Klein and colleagues previously reported that immunity from DTaP diminishes over time and suggested that health officials consider administering booster doses of the vaccine, currently given at 11 years, earlier. Other studies comparing the two pertussis vaccines have yielded similar results.
DTaP was introduced to replace the DTwP due to concerns about adverse effects with whole-cell pertussis, such as fever. Results from initial DTaP licensure studies suggested the acellular vaccine was just as efficacious as the whole-cell version, but recent data suggest this may not be the case.
In the most recent study, Klein and colleagues analyzed data from children born from 1994 to 1999 — the time period during which the United States was switching from DTwP to DTaP. Study participants received four pertussis-containing vaccines during the first two years of life and were aged 10 through 17 years during the California pertussis outbreak.
During the outbreak, 138 participants tested positive for whooping cough on polymerase change reaction (PCR) assay. The researchers used two control groups — 899 patients who tested negative on PCR and 54,339 who were not tested for pertussis, but who were matched by sex, race/ethnicity and medical clinic.
Among the 1,037 participants who underwent PCR testing, 234 received only DTwP doses, 606 received only DTaP doses and 197 received a mix of both vaccines during the first two years of life.
Participants who received four DTaPs had an 5.63 odds ratio for a positive pertussis test (95% CI: 2.55-12.46) compared with those who received four DTwPs.
Those who were administered mixed DTwP/DTaP vaccines had a 3.77 odds ratio (95% CI: 1.57-9.07), the researchers found. There was a significant increase in pertussis risk with a decreasing number of DTwP doses.
In terms of actual cases, among the 234 participants tested with PCR who received four DTwP shots, only eight had whooping cough (3.4%) vs. 111 of the 606 who received only DTaP (18.3%). There 19 whooping cough cases among the 197 participants whose four doses comprised a mix of the two vaccine types (9.6%).