Long-term immunogenicity of a single dose of acellular pertussis vaccine in paediatric health-care workers

Assessment of IgA anti-PT and IgG anti-ACT reflex testing to improve Bordetella pertussis serodiagnosis in recently vaccinated subjects

OBJECTIVES

Quantifying IgG antibodies to pertussis toxin (PT) is the most specific and sensitive method for the serodiagnosis of a Bordetella pertussis infection. Since PT is a component of acellular pertussis vaccines, anti-PT IgG is also induced by vaccination, precluding pertussis serodiagnosis based exclusively on anti-PT IgG in recently vaccinated subjects. Here, we aim to identify additional B. pertussis-specific serological markers that can discriminate between infection and recent vaccination.

METHODS

The clinical usefulness of measuring IgA directed to the vaccine antigen PT and IgG directed to non-vaccine antigens (Fim2/3, LPS, ACT, CatACT) was evaluated in nine well characterized subject groups, aged 10-89 years (n = 390). Serum anti-PT IgG levels (>125 IU/mL) served as an indicator for a recent B. pertussis infection. Comparing symptomatic pertussis-infected subjects (n = 140) with recently vaccinated, non-infected subjects (n = 100) revealed the optimal cut-off, accuracy, sensitivity and specificity for each single parameter.

RESULTS

For pertussis diagnosis in recently vaccinated subjects, the measurement of anti-PT IgA (cut-off 15 IU/mL) and anti-ACT IgG (cut-off 15 U/mL) resulted in accuracies of 95% (91.5-97.1) and 87.5% (82.7-91.1), sensitivities of 92.9% (87.4-96.0) and 83.6% (76.5-88.8) and specificities of 98% (93.0-99.4) and 93% (86.3-96.6), respectively. Comparing anti-PT IgA levels between the youngest (10-19 years, n = 38) and oldest (70-89 years, n = 17) age groups revealed an age-dependent increase in antibody levels in pertussis-infected subjects (p < 0.0001).

CONCLUSIONS

Reflex testing of anti-PT IgA and anti-ACT IgG improves pertussis serodiagnosis in recently vaccinated symptomatic subjects with elevated anti-PT IgG levels. Furthermore, both markers can discriminate between vaccination and recent infection in pertussis serosurveillance studies.

Immunization against pertussis in adolescents and adults

Pertussis is a highly contagious infectious disease caused by Bordetella pertussis that can be extremely serious, particularly in young infants. For many years the efforts of health authorities throughout the world to prevent pertussis had the main goals of reducing the morbidity of infants and children under 5 years of age, maintaining protection for several years during the school-age period and developing a significant herd immunity to directly and indirectly reduce the risk of the spread of the disease among young infants and the risk of transmission of the infection from preschool children to infants. However, the increased risk of B. pertussis infection among adolescents and adults due to the waning immunity to this bacterium induced by vaccines and natural infection seems to be the main reason for the resurgence of pertussis. We discuss the reasons for the administration of pertussis vaccines to individuals for whom they were previously not recommended, the expected results of the administration of additional pertussis vaccine doses and the differences in the administration of pertussis vaccines in different countries. An analysis of the literature revealed several reports indicating the need for the modification of immunization schedules against pertussis, with booster doses among adolescents and the need for the vaccination of pregnant women. However, to monitor the true epidemiology of pertussis, effective programmes to collect pertussis cases, adequate reporting systems and vaccination coverage monitoring should be urgently implemented.

Serum IgA responses against pertussis proteins in infected and Dutch wP or aP vaccinated children: an additional role in pertussis diagnostics

Background

Whooping cough is a respiratory disease caused by Bordetella pertussis, which induces mucosal IgA antibodies that appear to be relevant in protection. Serum IgA responses are measured after pertussis infection and might provide an additional role in pertussis diagnostics. However, the possible interfering role for pertussis vaccinations in the induction of serum IgA antibodies is largely unknown.

Methods/Principal Findings

We compared serum IgA responses in healthy vaccinated children between 1 and 10 years of age with those in children who despite vaccinations recently were infected with Bordetella pertussis. All children have been vaccinated at 2, 3, 4 and 11 months of age with either the Dutch whole-cell pertussis (wP) vaccine or an acellular pertussis (aP) vaccine and additionally received an aP booster vaccination at 4 years of age. Serum IgA responses to pertussis toxin (PT), filamentous heamagglutinin (FHA) and pertactin (Prn) were measured with a fluorescent multiplex bead-based immuno-assay. An ELISPOT-assay was used for the detection of IgA-memory B-cells specific to these antigens. Serum IgA levels to all pertussis vaccine antigens were significantly higher in infected children compared with healthy children. High correlations between anti-PT, anti-FHA or anti-Prn IgA and IgG levels were found in infected children and to some degree in wP primed children, but not at all in aP primed children. Highest numbers of IgA-pertussis-specific memory B-cells were observed after infection and generally comparable numbers were found after wP and aP vaccination.

Conclusions

This study provides new insight in the diagnostic role for serum IgA responses against PT in vaccinated children. Since aP vaccines induce high serum IgG levels that interfere with pertussis diagnostics, serum IgA-PT levels will provide an additional diagnostic role. High levels of serum IgA for PT proved specific for recent pertussis infection with reasonable sensitivity, whereas the role for IgA levels against FHA and Prn in diagnosing pertussis remains controversial.

Immunization of teenagers with a fifth dose of reduced DTaP-IPV induces high levels of pertussis antibodies with a significant increase in opsonophagocytic activity

Waning vaccine-induced immunity against Bordetella pertussis is observed among adolescents and adults. A high incidence of pertussis has been reported in this population, which serves as a reservoir for B. pertussis. A fifth dose of reduced antigen of diphtheria-tetanus-acellular-pertussis and inactivated polio vaccine was given as a booster dose to healthy teenagers. The antibody activity against B. pertussis antigens was measured prior to and 4 to 8 weeks after the booster by different assays: enzyme-linked immunosorbent assays (ELISAs) of IgG and IgA against pertussis toxin (PT) and filamentous hemagglutinin (FHA), IgG against pertactin (PRN), opsonophagocytic activity (OPA), and IgG binding to live B. pertussis. There was a significant increase in the IgG activity against PT, FHA, and PRN following the booster immunization (P < 0.001). The prebooster sera showed a geometric mean OPA titer of 65.1 and IgG binding to live bacteria at a geometric mean concentration of 164.9 arbitrary units (AU)/ml. Following the fifth dose, the OPA increased to a titer of 360.4, and the IgG concentration against live bacteria increased to 833.4 AU/ml (P < 0.001 for both). The correlation analyses between the different assays suggest that antibodies against FHA and PRN contribute the most to the OPA and IgG binding.

Health care workers and pertussis: an underestimated issue

PURPOSE

Communicable and vaccine-preventable airway infections are a major public and occupational health issue. The epidemiology of pertussis has changed, with unprotected adults being the main source of infections. Thus, the prevention of a transmission from health care workers (HCWs) to patients is an important strategy to control this communicable infection. The Standing Committee on Vaccination (STIKO) at the Robert Koch-Institute in Germany has explicitly recommended that HCWs ought to be vaccinated against pertussis. However, vaccination rates among HCWs remain low. This study was meant to evaluate the attitudes of HCWs towards the pertussis vaccination and to determine the correlation between the influenza and pertussis vaccination status of HCWs.

METHODS

An anonymous questionnaire was distributed to HCWs at a German university hospital.

RESULTS

Overall, we found a disturbingly low level of awareness concerning official recommendations as to immunizations (35.6%) and the personal risk assessment of acquiring a work-related pertussis infection (23.2%). In general, both aspects were frequently associated with a refusal to get immunized. A strong correlation between the immunization status of pertussis and influenza was found among physicians: overall, 93.1% of physicians who were vaccinated against pertussis were also vaccinated against influenza. Nurses showed significantly weaker correlation rates as well as lower vaccination rates (p<0.05).

CONCLUSIONS

Misconceptions about pertussis and low vaccination rates were prevalent among HCWs, particularly nurses. Hospital-based pertussis vaccination campaigns should focus on the risk of nosocomial pertussis transmission and on the new recommendations for pertussis immunization among adults and HCWs.