Are acellular vaccines as safe and effective as whole-cell vaccines for preventing pertussis (whooping cough) in children?
Multicomponent (i.e., three or more) acellular vaccines are as effective as whole-cell vaccines at preventing pertussis and mild pertussis disease (e.g., cold symptoms, cough without classic whoop or cough paroxysms) in children. Adverse effects are similar to those from placebo and less severe than those from whole-cell vaccines. (Strength of Recommendation = A, based on consistent, good-quality patient-oriented evidence.)
Worldwide, there are approximately 50 million cases of pertussis each year, leading to about 400,000 deaths. In recent years, high-income countries have seen large increases in adolescent pertussis rates; the incidence of pertussis in U.S. adolescents has risen 19-fold since 1996. Whole-cell vaccines have been available for 70 years. Concerns about adverse effects (e.g., convulsions, encephalopathy, hypotonic episodes, fever, vomiting) led to the development of acellular recombinant vaccines in the 1970s and 1980s; however, it was not definitively known whether acellular vaccines were as effective as whole-cell vaccines.
This Cochrane review included 52 safety trials and six effectiveness trials. The effectiveness of multicomponent vaccines was 84 to 85 percent in preventing pertussis, and 71 to 78 percent in preventing mild pertussis disease. In contrast, single-component (one to two) vaccines were 59 to 79 percent effective in preventing pertussis and 41 to 54 percent effective in preventing mild disease. The authors were unable to directly compare acellular with whole-cell vaccines because of the wide range of effectiveness of different whole-cell vaccines (36 to 95 percent), but both were found to be effective.
Acellular and whole-cell vaccines had a low incidence of adverse effects; however, in the acellular vaccine studies, more patients completed the series, fewer patients had febrile convulsions, and fewer patients experienced hypotonic-hyporesponsive episodes. Although not statistically significant compared with whole-cell vaccines, adverse effects from acellular vaccines increased as the series progressed, including fever (60 to 162 per 1,000 persons), local redness (96 to 162 per 1,000 persons), and swelling (117 to 275 per 1,000 persons). Deaths from infections and all causes were rare, and no difference was seen between vaccines.
Guidelines from the Centers for Disease Control and Prevention recommend acellular vaccines in all age groups. Recommendations include the diphtheria and tetanus toxoids and acellular pertussis (DTaP) combination vaccine at two, four, six, and 15 to 18 months of age, with a booster of the tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccine between 11 and 18 years of age, and a one-time Tdap booster as an adult. Clinicians should strongly recommend Tdap vaccination in adults who are in contact with infants younger than 12 months.1