Pertussis vaccination in mixed markets: Recommendations from the Global Pertussis Initiative

The Global Pertussis Initiative is an expert scientific forum that publishes consensus recommendations concerning pertussis for many regions of the world. Here, we give recommendations for the primary vaccination of infants in those countries where whole-cell pertussis (wP)- and acellular pertussis (aP)-containing combination vaccines are used in parallel. A selective literature review was performed concerning the influence on safety, immunogenicity, and effectiveness of mixing wP- and aP-containing vaccines for primary immunization of infants. In addition, local data were collected from various countries and the results discussed in a face-to-face meeting. Very few data addressing issues of mixing combination vaccines were identified, and no data were available concerning the effectiveness or duration of protection. It was also found that pharmacovigilance data are scarce or lacking in those countries where they would be needed the most. We then identified frequent problems occurring in low- and middle-income countries (LMICs) where both vaccine types are used. Relying on local knowledge, we give practical recommendations for a variety of situations in different settings. Specific needs for additional data addressing these issues were also identified. International bodies, such as the World Health Organization (WHO), as well as vaccine producers should try to find ways to highlight the problems of mixing wP- and aP-containing combination vaccines with robust data. Countries are urged to improve on their pharmacovigilance for vaccines. For practicing physicians, our recommendations offer guidance when wP- and aP-containing vaccines are used in parallel during primary immunization.

What to do and what not to do in serological diagnosis of pertussis: recommendations from EU reference laboratories

Bordetella pertussis-specific antibodies can be detected by enzyme-linked immunosorbent assays (ELISAs) or multiplex immunoassays. Assays use purified or mixed antigens, and only pertussis toxin (PT) is specific for B. pertussis. The interpretation of results can be based on dual-sample or single-sample serology using one or two cut-offs. The EU Pertstrain group recommends that: (i) ELISAs and multiplex immunoassays should use purified non-detoxified PT as an antigen, that they should have a broad linear range and that they should express results quantitatively in International Units per millilitre (IU/ml); (ii) a single or dual diagnostic cut-off for single-serum serology using IgG-anti-PT between 50 and 120 IU/ml should be used, and diagnostic serology cannot be validly interpreted for one year after vaccination with acellular pertussis (aP) vaccines; (iii) IgA-anti-PT should only be used with indeterminate IgG-anti-PT levels or when a second sample cannot be obtained. This group discourages using: (i) other antigens in routine diagnostics, as they are not specific; (ii) micro-agglutination, due to its lack of sensitivity; (iii) immunoblots for pertussis serodiagnosis, as results cannot be quantified; (iv) other methods, such as complement fixation or indirect immunofluorescence, due to their low sensitivity and/or specificity.

International Bordetella pertussis assay standardization and harmonization meeting report. Centers for Disease Control and Prevention, Atlanta, Georgia, United States, 19-20 July 2007

An international meeting on Bordetella pertussis assay standardization and harmonization was held at the Centers for Disease Control and Prevention (CDC), Atlanta, GA, 19–20 July 2007. The goal of the meeting was to harmonize the immunoassays used for pertussis diagnostics and vaccine evaluation, as agreed upon by academic and government researchers, regulatory authorities, vaccine manufacturers, and the World Health Organization (WHO).

The primary objectives were (1) to provide epidemiologic, laboratory, and statistical background for support of global harmonization; (2) to overview the current status of global epidemiology, pathogenesis and immunology of pertussis; (3) to develop a consensus opinion on existing gaps in understanding standardization of pertussis assays used for serodiagnosis and vaccine evaluation; and (4) to search for a multicenter process for addressing these priority gaps. Presentations and discussions by content experts addressed these objectives. A prioritized list of action items to improve standardization and harmonization of pertussis assays was identified during a group discussion at the end of the meeting. The major items included: (1) to identify a group that will organize, prepare, maintain, and distribute proficiency panels and key reagents such as reference and control sera; (2) to encourage the development and identification of one or more reference laboratories that can serve as an anchor and resource for other laboratories; (3) to define a performance-based assay method that can serve as a reference point for evaluating laboratory differences; (4) to develop guidance on quality of other reagents, e.g., pertussis toxin and other antigens, and methods to demonstrate their suitability; (5) to establish an international working group to harmonize the criteria to evaluate the results obtained on reference and proficiency panel sera; (6) to create an inventory to determine the amount of appropriate and well-characterized sera that are available globally to be used as bridging reagents for vaccine licensure; and (7) to seek specific guidance from regulatory authorities regarding the expectations and requirements for the licensure of new multicomponent pertussis vaccines.

Pertussis: An old disease in new clothes

In this issue of Eurosurveillance, two articles report data about pertussis.

[Pertussis: incidence, symptoms and costs]

BACKGROUND AND OBJECTIVE

A prospective sentinel study into the population-based incidence of pertussis in adults was done between 2001 and 2004 in Rostock (former East Germany) and Krefeld (former West Germany).

PATIENTS AND METHODS

971 outpatients, who consulted general practitioners or internists, were included. Clinical inclusion criteria were coughing for one week or more and no chronic respiratory diseases. Bordetella infection was diagnosed by PCR on nasopharyngeal swabs and ELISA for serology (IgG-anti-PT, IgA-anti-PT, IgG-anti-FHA, IgA-anti-FHA).

RESULTS

We found a total of 97 cases of pertussis in this cohort. The main symptom was coughing for a median of 7-8 weeks. Population-based incidence was estimated in Krefeld at 169 cases/100000 population per year, and in Rostock at 160/100000 per year. Resource use was 120 EUR of direct medical cost and 434 euro of indirect medical cost, not including hospitalization in this study.

CONCLUSIONS

Pertussis is a frequent cause of longer lasting cough in German adults, and it causes significant morbidity and costs.

Pertussis of adults and infants

Bordetella pertussis continues to circulate even in populations where a high vaccine coverage of infants and children is achieved. Cases in adolescents and adults are reported with increasing frequency in many countries. Adults are a reservoir for infections in very young infants, in whom pertussis may be severe and life-threatening. The salient clinical feature of pertussis in adolescents and adults is prolonged coughing, and recognising that pertussis does occur in these age groups is the most important step in its diagnosis. A laboratory diagnosis can be made by bordetella-PCR from nasopharyngeal swabs or secretions and by detection of antibodies, mainly to pertussis toxin; laboratory diagnosis is, however, not well standardised. Vaccination of adolescents and adults is now possible with acellular pertussis vaccines, which are well tolerated, immunogenic, and effective. Adolescent boosters and the vaccination of health-care workers are already included in vaccination calendars in some countries. Vaccine-recommending bodies and national health-care organisations must have locally relevant information on the transmission of pertussis from adults to infants to be able to make decisions on the advisability, feasibility, and priority for booster immunisation against pertussis.

Effectiveness of acellular pertussis vaccine assessed by hospital-based active surveillance in Germany

We assessed the effectiveness of complete and partial pertussis vaccination in Germany--a country where acellular vaccine is predominantly used--for the prevention of cases of pertussis requiring hospitalization. Vaccine effectiveness was estimated by means of a screening method. Vaccine coverage of children born during the period of June 1996 through December 1998 was assessed by a telephone survey. Data from hospitalized children with pertussis in 1997-1998 and from patients with pertussis complications in 1997-2000 were acquired by a nationwide, hospital-based, active surveillance system. Age-adjusted vaccine effectiveness of completed primary vaccination was estimated to be 99.8% (95% confidence interval [95% CI], 98.9-100). After receipt of 1 dose of vaccine, vaccine effectiveness was as high as 68.0% (95% CI, 45.6-81.1), increasing to 91.8% (95% CI, 84.7-95.7) after receipt of the second dose. Vaccine effectiveness was even slightly higher for pertussis with complications. Thus, even after partial vaccination, acellular pertussis vaccine is highly effective in preventing hospitalizations for pertussis.

Recommendations are needed for adolescent and adult pertussis immunisation: rationale and strategies for consideration

Pertussis vaccination of infants has dramatically reduced disease, complications and deaths in infancy and early childhood. But there is still a major public health challenge--to deal with the morbidity and economic burden of illness in older children, adolescents and adults. Furthermore, it is these groups that form a major source of infection for non-immunised and partially immunised infants who are at high risk of severe complications. Adult-type acellular pertussis vaccine confers safe and effective protection against pertussis. There are several strategies to consider for immunising older individuals. Universal vaccination of all age groups would be the best available strategy for protecting individuals. It would also reduce the potential for transmitting the disease to other susceptibles, particularly infants. However, such a policy may be difficult both logistically and economically at this time. More easily achievable as a first step would be a strategy of universal adolescent booster vaccination combined with a programme targeted at adults most likely to have contact with very young babies including healthcare and childcare workers, parents and close family contacts. There is also potential for offering vaccination to adults (and their carers and close contacts) whose medical conditions or advanced age may place them at increased risk of more severe pertussis disease. Specific details of immunisation programmes must be made on a country by country basis depending on local circumstances.

Stability of antibodies to Bordetella antigens in German adults

To estimate the rate of asymptomatic exposure to Bordetella pertussis antigens in the German adult population and to evaluate the stability of antibodies to these antigens, antibody levels against Bordetella antigens and their variability over time were measured in German adult blood donors. One hundred forty-six regular blood donors (41 females, 105 males) were tested repeatedly for antibodies of isotypes IgG and IgA to pertussis toxin, filamentous hemagglutinin (FHA) and pertactin over a period of 2-5 years. Overall, 86% and 56% had IgG or IgA antibodies to pertussis toxin, respectively, 100% and 92% had IgG or IgA antibodies to FHA, respectively, and 83% and 93% had IgG or IgA antibodies to pertactin, respectively. One significant titer increase of both IgG anti-FHA and IgG anti-pertactin, one of IgG anti-FHA, and two of IgA anti-FHA as well as one significant decrease of IgG anti-pertussis toxin were observed during an observation period of 480.5 person-years. Antibody concentrations in men and women were not different. The data show that the level of antibodies to pertussis toxin, FHA, and pertactin remains stable over several years. Furthermore, depending on the definition of serological evidence, the rate of significant increases or decreases suggesting unrecognized exposure to Bordetella antigens was estimated to be between <0.2 and 1.0 per 100 person-years in the population studied.

Pertussis in Germany: regional differences in management and vaccination status of hospitalized cases

The incidence of pertussis requiring hospitalization in children younger than 16 years was estimated by the use of an active surveillance-system. Of special interest were differences between West and East Germany following different vaccination strategies before reunification. In 1997 and 1998, 754 pertussis cases required a total of 11,151 hospital inpatient days. The incidence of hospitalized pertussis was 2.68/100,000 person years and this was significantly higher in East than in West Germany. In East Germany an unusually high percentage of hospitalized cases was found in children aged 6-15 years (45% versus 13% in West Germany). The difference between the regions may be due either to a different perception of the disease or to an increased immunity induced by prior disease or vaccination. In East Germany, pertussis was rare until reunification but it has increased significantly since then. Older children may thus represent a population at risk of pertussis having not had previous exposure to pertussis antigens.

Epidemiological typing of Bordetella pertussis isolates: recommendations for a standard methodology

Pertussis is re-emerging in vaccinated populations, and to gain insight into the reasons for this development population-based studies are necessary. Unfortunately, various techniques are used to study Bordetella pertussis populations, hampering comparison between studies. A standard methodology for epidemiological typing of Bordetella pertussis isolates is proposed which is based on serotyping, pulsed-field gel electrophoresis and gene typing. Such a standard approach will allow comparisons between studies performed in different laboratories. Comparisons may reveal whether the epidemiological differences observed between countries are due for instance to different Bordetella pertussis populations or different vaccines used.

Evaluation of a single-sample serological technique for diagnosing pertussis in unvaccinated children

This study was performed to evaluate the sensitivity of immunoglobulin (Ig)G and IgA antibodies to pertussis toxin and filamentous hemagglutinin in diagnosing pertussis from a single serum sample. The pertussis group was defined according to the World Health Organization pertussis case definition. The control group coughed for 21 days or more but had no microbiological or serological evidence of Bordetella infection. Both cohorts were divided into infants (< 12 months of age), toddlers (1-4 years) and school children (5-10 years). There were 525 subjects in the pertussis group and 321 in the control group, with an even distribution of genders. IgG and IgA antibodies to pertussis toxin and filamentous hemagglutinin were measured in a standardized enzyme immunoassay. Antibody levels beyond the 95 percentile of the control cohort were regarded as indicative of recent contact, setting the specificity level at 0.95. Acute serum samples drawn between 1 week and 3 weeks after the onset of coughing showed a low sensitivity (2-19%) for diagnosing pertussis. In convalescent samples taken 5-10 weeks after the onset of symptoms, detection of IgG anti-pertussis toxin was the best single test, with a sensitivity of 61%, 65%, and 74% in infants, toddlers and school children, respectively. A combination of IgG anti-pertussis toxin and IgA anti-filamentous hemagglutinin using age-specific reference values had a sensitivity of 81-89% in diagnosing pertussis from a single serum sample taken 5-10 weeks after the beginning of symptoms.

Pertussis complications in Germany--3 years of hospital-based surveillance during the introduction of acellular vaccines

Between 1 November 1993 and 31 October 1996, admissions to paediatric departments for Bordetella pertussis complications were reported to a nationwide, hospital-based active surveillance system. The case definition included pertussis complicated by pneumonia, apnoea requiring assisted ventilation, seizures, encephalopathy or a combination of these. Two hundred sixteen cases of pertussis complications were registered. 57.4% of them were in infants, 50.9% of them less than 6 months old. There were five deaths, three previously healthy children died. At the time of hospital admission, 106 cases would have been eligible for at least three doses of pertussis vaccine, only four (3.8%) had received the recommended number of immunisations. From the second quarter of 1995, the reported number of cases declined. The decrease coincides with an improvement of pertussis vaccination coverage between 1992 and 1995 due to an increased use of acellular vaccines. The reduction of complicated pertussis was observed even in age-groups too young for the recommended vaccinations. The observed decrease could be due to the increase in vaccination coverage with interruption of the chain of transmission to the younger age-groups, to a cyclic decrease in pertussis cases, or to a combination of both. Continued surveillance will provide information on the epidemiological trend of hospitalisations for pertussis complications in the first European country to have introduced vaccination with acellular vaccines on a large scale.

A serologic study of organisms possibly associated with pertussis-like coughing

OBJECTIVE

To assess the frequency of serologic evidence for an infection with microorganisms other than Bordetella pertussis in children with pertussis-like coughs.

METHODS

The study was performed within a protective efficacy trial of an acellular pertussis vaccine. Children who coughed for >7 days and had no laboratory evidence of recent infection with B. pertussis were eligible for the present study. Antibodies to Mycoplasma, Chlamydia, respiratory syncytial virus and influenza viruses A and B were measured by complement fixation, and antibodies to adenovirus and parainfluenza viruses 1, 2 and 3 were measured by enzyme-linked immunosorbent assay (ELISA) in acute and convalescent serum samples. Significant titer rises (4-fold titer rise in complement fixation, 100% increase of units in ELISA) and concentrations of antibodies beyond age-specific reference values were regarded as indicative of recent infection. In some children IgM antibodies to Epstein-Barr virus and to cytomegalovirus were also measured by ELISA.

RESULTS

A total of 149 of 1179 (12.6%) children had no laboratory evidence of B. pertussis infection. Serologic evidence for other infections were found in 56% (83 of 149). Adenovirus (33), parainfluenza viruses 1, 2 and 3 (18), Mycoplasma pneumoniae (15) and respiratory syncytial virus (14) were most common. Of this group 48% had been vaccinated against pertussis.

CONCLUSION

We present data that a proportion of pertussis-like coughs in children may be caused by adenovirus, parainfluenza viruses, respiratory syncytial virus and Mycoplasma. The differential diagnosis of pertussis-like coughs by laboratory methods should include these infections, especially in vaccinated children.

Factors influencing the spread of pertussis in households

The objective of this study was to compare the spread of pertussis in children and adults being secondary contacts after household exposure. The study was nested in an efficacy trial of an acellular pertussis vaccine. The spread of the disease was also monitored with respect to gender and antibiotic therapy. A total of 453 index cases, of which 133 were monitored for adult disease, fulfilled the WHO definition of pertussis. They had contacts to 173 unvaccinated children aged 6-47 months, and a total of 101 adults with pertussis were followed. Detection of the bacteria, or a significant increase of specific antibodies confirmed the diagnosis. Secondary spread of the disease was assumed, when a household member coughed for 7 days or more and had laboratory evidence for pertussis. Crude attack rates (AR) were 69% in children and 31% in adults (P < 0.05). AR in children were independent of gender but more women than men (P=0.02) were affected in those households where the index case was a child. Erythromycin treatment of the index case reduced the AR in exposed toddlers from 80% to 57% (P=0.06), and in exposed adults from 40% to 21% (P=0.2). Erythromycin therapy in contacts did not alter the clinical course of the disease significantly.

CONCLUSIONS

In a household study of pertussis, 69% of children and 31% of adults (more women than men) contracted the disease. Erythromycin reduced the number of infections in household contacts, but did not alter the clinical course in those who contracted pertussis.

Acinetobacter baumannii colonization in ventilated preterm infants

The role of Acinetobacter baumannii in infections in ventilated preterm infants was evaluated in 15 colonized infants (11 male, 4 female) in a pediatric intensive care unit. These cases were randomly matched by birth weight and gestational age with ventilated non-colonized controls (8 male, 7 female). Case records were reviewed for signs and symptoms of infection. Colonized infants were ventilated significantly longer (p < 0.05) than controls, and had body temperatures of > 37 degrees C for a significantly longer period of time (p < 0.05). No other parameter of infection differed significantly between the groups. The duration of intensive care treatment did not differ between cases and controls, nor did the weight gain during intensive care treatment. No fatalities occurred in either group.

Immunogenicity and reactogenicity of HbOC vaccine administered simultaneously with acellular pertussis vaccine (DTaP) into either arms or thighs of infants

To evaluate the reactogenicity and immunogenicity of a Haemophilus influenzae type b conjugate vaccine (HbOC) and of a tricomponent acellular pertussis vaccine (DTaP) when injected simultaneously into either contralateral arms or into contralateral thighs, 110 infants were enrolled to receive three doses of DTaP at 3, 4, and 5 months and two HbOC doses at 3 and 5 months of age. Administration of either of the two vaccines into arms was associated with significantly more local side effects than administration into thighs. There was no difference in geometric mean concentration (GMC) values for any of the four vaccine antigens between subjects who had been vaccinated into arms or thighs. After immunization, all children had protective antibody titers to diphtheria toxin. While post vaccination the mean anti-tetanus toxoid GMC was > or = 1.25 IU/ml, there was no significant rise as compared to the GMC before vaccination. GMCs of antibodies against the various pertussis antigens were similar to those observed before with the same DTaP vaccine. The simultaneous administration of DTaP and HbOC was safe and immunogenic irrespective of the site of vaccine administration, but significantly more local reactions occurred when vaccines were injected into arms.