Rationale for pertussis booster vaccination throughout life in Europe

Although the introduction of universal pertussis immunisation in infants has greatly reduced the number of reported cases in infants and young children, disease incidence has been increasing in adolescents and adults in recent years. This changing epidemiological pattern is probably largely attributable to waning immunity after natural infection or vaccination. Furthermore, improved diagnostic testing, active surveillance, changes in disease susceptibility, vaccine characteristics, and increased awareness of the disease might also be contributing factors. Susceptibility to pertussis in adolescents and adults results not only in direct morbidity in these age groups, but also poses a transmission risk to susceptible non-immune infants who are often too young to be vaccinated. Because vaccination schedules vary across Europe, we review the pertussis situation in this region and propose considerations for use of pertussis booster vaccinations at different ages to reduce individual morbidity and transmission from present rates and increase herd protection.     

Pertussis – eine impfpräventable Erkrankung

Pertussis (whooping cough) is caused by Bordetella pertussis and B. parapertussis. It is a purely respiratory infection, which can be highly contagious. In countries with vaccination programs, the main targets are young infants, older non-vaccinated children, adolescents and adults. The disease remains endemic and cyclical worldwide, even in countries with a sustained high vaccination coverage. Pertussis is a notifiable disease in Germany but epidemiological data might not reflect the true burden of the disease. The main symptom is coughing for prolonged periods, which can be paroxysmal. The disease can take a severe course in infants with a possible fatal outcome but adults can also have a high rate of complications. Pertussis can be diagnosed by detecting Bordetella DNA by PCR or by detection of IgG antibodies to pertussis toxin. Antibiotics, such as macrolides can stop transmission but might not relieve the symptoms. Infant vaccination, which in Germany is carried out with four doses of combination vaccines with acellular pertussis components, can prevent the majority of cases. As immunity after infection and vaccination is not permanent, additional strategies comprising school entry boosters and the vaccination of adolescents and adults, as well as vaccinating special risk groups, such as pregnant women are recommended.     

Tos ferina en España. Situación epidemiológica y estrategias de prevención y control. Recomendaciones del Grupo de Trabajo de Tos ferina

A large increase of pertussis incidence has been observed in recent years in countries with high vaccination coverage. Outbreaks of pertussis are increasingly being reported. The age presentation has a bipolar distribution: infants younger 6 months that have not initiated or completed a vaccination schedule, and adolescents and adults, due to the lost of natural or vaccine immunity over time. These epidemiological changes justify the need to adopt new vaccination strategies in order to protect young infants and to reduce pertussis incidence in all age groups.     

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.     

Conduite à tenir devant un ou plusieurs cas de coqueluche

The evolution of the epidemiology of pertussis, new licensed macrolides and vaccines, new recommendations for vaccination among adolescents and adults need an update of the French guidelines for prevention of the disease around one or grouped cases of the disease. A particular attention should be raised to the diagnosis of whooping cough in adults who are presently the main reservoir of Bordetella pertussis. Whooping cough in adults presents as an unexplained prolonged cough with nocturnal exacerbation witch accounts for most of the contaminations of young infants. A bacteriological confirmation of pertussis should be provided before implementation of preventive measures: culture and PCR are presently the gold standard for the diagnosis of pertussis in infants, children and even adults who have been coughing for less than 20 days. Later on, serology (Elisa, immuno-empreinte) is the only technique available, but cannot be interpreted if the patient has been vaccinated less than one year ago. Infants under three months should be admitted to hospital and every case submitted to respiratory isolation. Eviction from the community should be pronounced within the five first days following the onset of an effective antibiotic treatment. New macrolides should be favoured: clarithromycine for seven days or azithromycine for five days. Household contacts should be given the same prophylactic antibiotic treatment: children and adolescent not correctly immunized, parents of the index case as adults parents of not or not completely immunized infants. The vaccination program of the household should be updated. The same measures should be applied in case of grouped cases (at least two contemporary or consecutive cases in the same area). In that case, the Public Health System doctors should be involved in the investigation and the classification of the cases. The close contacts not or not completely immunized should be prescribed and antibiotic prophylaxis and an update of their vaccination program. Among the occasional contacts, high-risk people only should be treated. In the day care centres an antibioprophylaxis should be given to children who have received less than four vaccine shots against pertussis and to the personnel contact to the cases as well. In the schools, the antibiotic prophylaxis should be prescribed to all children of the classroom(s) not completely vaccinated and to the teacher(s) as well. In the boarding schools and institutions with handicapped children, antibiotic prophylaxis could be applied to every member if the pertussis vaccine coverage is at less than 50%. In hospitals, coughing personnel should wear masks and investigations towards pertussis should be performed in people with a more than seven day unexplained cough. Preventive measures should be applied in case of confirmation of pertussis.     

Recent developments in pertussis

Pertussis causes nearly 300,000 deaths in children every year. Most deaths take place in developing countries, but the infection remains a priority everywhere. Pertussis vaccination protects infants and children against death and admission to hospital, but breakthrough disease in vaccinated people can happen. In high-mortality countries, the challenge is to improve timeliness and coverage of childhood vaccination and surveillance. In regions with low mortality and highest coverage, pertussis is frequently the least well-controlled disease in childhood vaccination programmes. Some countries have reported a rise in pertussis in adolescents, adults, and pre-vaccination infants, but how much these changes are real or a result of improved recognition and surveillance remains uncertain. In response, several countries have introduced adolescent and adult acellular pertussis vaccine boosters. The effect so far is unknown; assessment is impeded by poor data. Uncertainties still persist about key variables needed to model and design vaccination programmes, such as risk of transmission from adults and adolescents to infants. New vaccination strategies under investigation include vaccination of neonates, family members, and pregnant women.     

Progress in the diagnosis,prevention, and treatment of pertussis

Pertussis (“whooping cough”), caused by the gramnegative pleomorphic bacillus Bordetella pertussis, is a highly contagious, potentially life-threatening respiratory tract illness that has re-emerged worldwide as a cause of substantial morbidity and mortality in infants, children, and adolescents, even in countries with high vaccination rates. Waning immunity after immunization during childhood has been associated with a growing pool of susceptible adolescents and adults who are capable of transmitting pertussis to vulnerable unvaccinated or incompletely vaccinated infants. The use of acellular pertussis vaccine boosters in adolescents has been proposed and is likely to be recommended. Active immunization and improved methods for early diagnosis are key in the management of pertussis, and represent the most rapidly evolving aspects of this disease.     

Evidence of Bordetella pertussis infection in adults presenting with persistent cough in a french area with very high whole-cell vaccine coverage

Although France has had a vaccination program for 40 years, since 1990, an increase in whooping cough cases with parent-infant transmission has been observed. This study prospectively assessed the frequency of Bordetella pertussis infection in adults who consulted general practitioners for a persistent cough without an evident diagnosis. Among 217 patients, 70 (32%) confirmed whooping cough cases were identified. One case was culture positive, 36 were polymerase chain reaction positive, and 40 had increases or decreases of > or =2-fold in anti-pertussis toxin IgG titer between serum samples collected during the acute and convalescent phases. The median duration of cough in confirmed cases was 49 days (range, 13-123 days). Of the patients, 60% reported vaccination, and 33% reported whooping cough in infancy. Pertussis should be considered for diagnosis of acute and chronic cough in adults. Future studies should evaluate the public health interest of booster doses of pertussis vaccine in adults.     

Adults are whooping, but are internists listening?

Although studies have shown that pertussis is responsible for approximately 20% to 30% of cases of cough lasting more than 2 weeks in adults and adolescents, physicians have generally considered pertussis a disease that affects only children. Epidemiologic trends demonstrate that the incidence of pertussis has been rising, especially in adolescents and adults. Consequently, pertussis is not a "zebra" diagnosis but deserves a place among the community-acquired list of adult pathogens. Increased awareness among physicians about pertussis is important because adults may transmit the infection to infants, in whom the disease often leads to hospitalization and may result in death. Reporting this disease to the local health department is critical to its control because both case-patients and their close contacts should receive antimicrobial prophylaxis. A booster vaccine for adolescents and adults is likely to become available in the near future, so this is an important time to ensure that all physicians, not just pediatricians, are knowledgeable about the diagnosis, treatment, and reporting requirements for pertussis.     

A community-wide pertussis outbreak: an argument for universal booster vaccination

BACKGROUND: Pertussis incidence has increased in the United States since 1980, punctuated by outbreaks that involve adults and adolescents. We investigated a community-wide outbreak and studied risk factors among adults to identify prevention and control opportunities. METHODS: We analyzed surveillance data, interviewed patients, visited outbreak sites, and conducted a case-control study of risk factors for first-in-household adult infection during a Jackson County, Oregon, outbreak in 2003. RESULTS: In Jackson County, 135 pertussis cases were reported; the incidence was 71 per 100 000 population compared with 0 to 1 per 100 000 population from 1995 through 2001. Case investigations identified 2658 close contacts (19.7 per case); 1050 (40%) received antibiotic prophylaxis. Older children and adolescents (aged 10-17 years) and adults (aged > or =18 years) accounted for 67% of cases. Five infants were hospitalized (192 hospitalizations per 100 000 infants) compared with 18 in the remainder of the state (33 per 100 000 infants). Many cases occurred among epidemiologically linked clusters of varied composition, such as jail inmates and employees, methamphetamine users, low-income housing residents, school students and employees, and employees in certain work settings. Adult patients were more likely than controls to live with children aged 6 to 10 years (odds ratio, 6.4; 95% confidence interval, 1.8-23.4) and less likely to report a complete childhood vaccination history (odds ratio, 0.1; 95% confidence interval, 0.003-0.9). CONCLUSION: The predominance of adolescent and adult cases, appearance of new clusters despite aggressive control efforts, clustering of cases in hard-to-reach populations, and absence of modifiable risk factors for adult disease in this outbreak all suggest that universal booster vaccination of adolescents and adults might offer the only effective means to prevent such events in the future.     

Pertussis-induced cough

Pertussis (whooping cough) is one of the commonest vaccine preventable diseases in the UK, despite vaccination coverage being maintained for the last 15 years at over 90% among infants and the addition of a pre-school booster to the UK national immunisation programme in 2001. However, it is known that pertussis vaccine does not confer long-term immunity to clinical infection. Evidence of pertussis infection has been reported in 37% of children presenting in UK primary care and 20% of adolescents and adults presenting in Canadian health centres with persistent cough. In children and adults with persistent cough, paroxysmal coughing is the most sensitive indicator of pertussis, but has poor specificity and limited diagnostic value. Vomiting and whooping, particularly in combination, are stronger predictors of pertussis. Cough duration is longer in children than in adults with pertussis (median cough duration 112 days versus 42 days); individuals may take even longer to recover fully and regain previous levels of exercise tolerance. A diagnosis of pertussis may be confirmed by culture, Polymerase Chain Reaction (PCR) or serology. Single estimates of anti-pertussis toxin (PT) antibody titres in blood or oral fluid samples are highly specific. There are currently no proven efficacious treatments for pertussis-induced cough. Treatment with macrolide antibiotics reduces the duration of an individual's infectious period, but does not alter the duration of cough. Further research is needed to re-examine the epidemiology of pertussis in countries with different vaccination schedules, find efficacious treatments and develop methods of measuring cough frequency and severity in patients with pertussis-induced cough.     

Patterns of susceptibility in an outbreak of Bordetella pertussis: Evidence from a community-based study

OBJECTIVE:

To describe an outbreak of Bordetella pertussis and to assess which factors were associated with the development of clinical pertussis in children and adults during the outbreak.

DESIGN:

A case series was described to define the epidemiology of the pertussis outbreak. A school-based survey of children was used to measure the incidence of clinical pertussis over the previous six months. Vaccination records from the local public health facility were used to look at the relationship between age and vaccination parameters, and susceptibility to clinically diagnosed pertussis. A cross-sectional survey of teachers, parents and some hospital workers was used to assess these associations in adults.

SETTING:

An outbreak of pertussis in an isolated northern community in British Columbia.

POPULATION STUDIED:

All children in the community who attend daycare, kindergarten or school, and their parents were surveyed. In addition, some health care workers and mothers of preschool children were surveyed.

MAIN RESULTS:

A total of 31 suspected cases of pertussis were identified over a three-month period. Ninety per cent of the affected children who had available vaccination records had received four or five doses of pertussis vaccine. Sixty per cent of the town''s 209 children returned completed surveys. Of these, 69% had available vaccination records. Thirty-six children (28%) reported symptoms that fit the case definition for pertussis over the previous three months. Attack rates were highest for the group of children aged 10 to 14 years. In a multivariate logistic regression analysis, receiving prophylactic medication and an increased number of years from the last vaccine dose were found to be significant predictors for developing pertussis. Thirty-four per cent of the estimated 291 adults in the community returned completed surveys. The attack rate of pertussis in the adults was only 9%. Being a member of the school staff and/or having a household contact with pertussis were significant predictors of developing pertussis.

CONCLUSIONS:

Immunity to pertussis appears to wane during childhood. Peak susceptibility appears to be during early adolescence. Adults do not seem to be at greater risk than adolescents for developing the disease, but it seems unlikely that this is due to better immunity. Rather, it is probably related to a lower risk of exposure to pertussis and a lower rate of progression to symptomatic disease when adults are infected.Key Words: Immunity, Pertussis, VaccinationVaccination against Bordetella pertussis has resulted in a dramatic reduction in the incidence of this disease in Canada. Outbreaks of pertussis, however, still occur. While many outbreaks reported elsewhere occur in populations where vaccination rates have declined, many others occur in populations with high vaccination coverage (1,2). This has not changed with the introduction of the acellular pertussis vaccine. The reasons for this are not clear, but waning immunity and the transmission of disease from adolescents and adults to younger children have been proposed as possible mechanisms (3,4). An additional constraint in studying this problem is that there is no known level of antibody that can be shown to be protective against developing pertussis (5).The idea of waning immunity has been challenged recently. De Serres and colleagues (6) found that the attack rates were the same in adolescent (12%) and adult (11%) household contacts of pertussis index cases. The authors (6) felt that this similar attack rate was more consistent with a decreasing proportion of susceptible subjects with age and with longlasting immunity. They did not suggest that this immunity comes solely from vaccination, but more likely from subclinical boosting from endemic disease. Clearly, this has implications as to the utility of introducing an adolescent booster dose to reduce further the incidence of disease in the population.In May 2000, an outbreak of pertussis was reported in an isolated northern community in British Columbia. Pertussis outbreaks have been known to occur in three- to five-year cycles in British Columbia. The last such outbreak occurred in 1996 and 1997, and resulted in more than 1100 reported cases. Increased rates of pertussis transmission had already been reported throughout the province since January 2000 (British Columbia Centre for Disease Control, internal report). By mid-May 2000, nearly 400 cases had been reported to the British Columbia Centre for Disease Control. Rates of infection were highest among young adolescents (aged 10 to 14 years), followed by older children (aged seven to nine years). The Northwest Coastal Health Services Society (the region that includes the town of Stewart) was not among those health regions that had previously reported increased numbers of cases.The town of Stewart, which has a population of approximately 500 people, has one health centre for both curative and preventive care, and is more than 150 km from the nearest settlement (excluding the hamlet of Hyder, Alaska, which is only 1.6 km away). There are three schools - a public primary school, a public secondary school and a small, private Christian school. The local health region and the Department of Health Care and Epidemiology at the University of British Columbia initiated an investigation of the pertussis outbreak in Stewart. It was thought that the relative isolation of the community and its small size would allow investigators to see whether immunization status, age and the length of time from the last vaccine dose would significantly affect disease attack rates. It was hoped that vaccination records for most of the town''s children could be verified and then compared with the results of a school-based survey for pertussis-like symptoms. As well, a survey of adults was undertaken to determine whether symptoms also occurred in this susceptible group, and whether this was related to recalled vaccination history. Disease control measures (7), including erythromycin prophylaxis of close contacts of index cases and enhanced surveillance among symptomatic individuals, had already been implemented before the present study was undertaken and were not interrupted during the course of the study.     

Pertussis: increasing disease as a consequence of reducing transmission

Since the 1980s, the occurrence of pertussis cases in developed countries has increased and shifted towards older age groups. This resurgence follows 30 years of intense mass vaccination, and has been attributed primarily to three factors: (1) more effective diagnosis of the disease, (2) waning of vaccine-induced immunity, and (3) loss of vaccine efficacy due to the emergence of new Bordetella pertussis strains. Here we develop and analyse a mathematical model to assess the plausibility of these hypotheses. We consider that exposure to B pertussis through natural infection or vaccination induces an immune response that prevents severe disease but does not fully prevent mild infections. We also assume that these protective effects are temporary due to waning of immunity. These assumptions, describing the mode of action of adaptive immunity, are combined with a standard transmission model. Two distinct epidemiological scenarios are detected: under low transmission, most infections lead to severe disease; under high transmission, mild infections are frequent, boosting clinical immunity and maintaining low levels of severe disease. The two behaviours are separated by a reinfection threshold in transmission. As a result, the highest incidence of severe disease is expected to occur at intermediate transmission intensities--near the reinfection threshold--suggesting that pertussis resurgence may be induced by a reduction in transmission, independently of vaccination. The model is extended to interpret the outcomes of current control measures and explore scenarios for future interventions.     

Outbreak of pertussis on a college campus

Background

Pertussis is increasing among adolescents and adults despite universal childhood vaccination. This investigation describes an outbreak of pertussis among undergraduate students and assesses the burden of cough illness on a college campus.

Methods

Students presenting with prolonged cough were evaluated with culture, polymerase chain reaction (PCR), and serology. An e-mail survey was performed to determine the burden of cough illness on campus.

Results

Thirty-seven undergraduates were evaluated. Their mean duration of cough was 28 days. No student had cultures positive for B. pertussis; one was PCR positive. Ten (27%) had serologic values consistent with acute pertussis infection. The e-mail survey was returned by 225/500 (45%) students. Of these, 66 (29%; 95% confidence interval [CI], 23%-36%) reported a cough of 2 weeks or longer duration during the fall semester. A conservative estimate showed that the campus-wide incidence of a cough illness meeting the Centers for Disease Control and Prevention case definition for pertussis was 13% (95% CI, 10%-16%) during the fall semester.

Conclusions

Adolescents and young adults are susceptible to pertussis infection. This study demonstrates that there was a substantial rate of pertussis infection during an outbreak on a college campus. Our findings support the routine use of the acellular pertussis vaccine in adolescents and adults.     

Evolución de los casos de tosferina tras la vacunación de la embarazada y la pandemia COVID-19

BackgroundWhooping cough has had an increased incidence and severity specially in infants and maternal immunization has been implemented as a prevention strategy. COVID-19 pandemic seems to decrease the incidence of other respiratory diseases.MethodsRetrospective study from 2012 to 2021 to assess the influence of pertussis maternal immunizations and the first year of COVID-19 pandemic in the cases of whooping cough.Results960 suspected cases from primary care and hospital, with 130 cases (104 children and 26 adults) being diagnosed of whooping cough. In the post-vaccination period, a reduction in the cases and severity in infants up to 6 months old was observed as well as in the pertussis diagnosis in adult women. There were no whooping cough cases during the COVID-19 period.ConclusionsBoth the pertussis vaccination in pregnancy and the first year of the COVID-19 pandemic have decreased the number of pertussis cases.     

Mass vaccination of children with pertussis toxoid--decreased incidence in both vaccinated and nonvaccinated persons.

During 1979-1995, there was no vaccination against pertussis in Sweden. With the aim of studying the epidemiology and transmission of pertussis, mass vaccination with pertussis toxoid of children born during the 1990s was instituted in the G?teborg area (population, 778,597) in 1995. Infants were offered 3 doses of pertussis toxoid combined with diphtheria and tetanus toxoids. Children aged > or =1 year were offered 3 doses of pertussis toxoid alone. From June 1995 through February 1999, 167,810 doses of pertussis toxoid were given to 61,219 children born during the 1990s (56% received 3 doses). The number of Bordetella pertussis isolates per year declined from 1214 (1993-1995) to 64 (January 1997 through June 1999; P<.0001), and hospitalizations due to pertussis declined from 62 to 5 (P<.0001). Significant decreases in B. pertussis isolates and hospitalizations occurred in all age groups, including adults and nonvaccinated infants. Thus, mass vaccination of children with pertussis toxoid decreases spread of B. pertussis in the population.     

Consensus on the clinical and microbiologic diagnosis of Bordetella pertussis, and infection prevention. Expert Group on Pertussis Vaccination

Pertussis continues to be responsible for a significant disease burden worldwide. Although immunization practices have reduced the occurrence of the disease among children, waning vaccine- and infection-induced immunity still allows the disease to affect adolescents and adults who, in turn, can transmit the disease to non-immunized or partially immunized infants. This document is the result of a meeting in Mexico City of international experts who analyzed recent medical information in order to establish the current status of the epidemiology, diagnosis and surveillance of pertussis and, especially, the value of the dTpa booster dose in adolescents and adults as a pertussis prevention strategy in Mexico.     

Oligosaccharide conjugates of Bordetella pertussis and bronchiseptica induce bactericidal antibodies, an addition to pertussis vaccine

Pertussis is a highly contagious respiratory disease that is especially dangerous for infants and children. Despite mass vaccination, reported pertussis cases have increased in the United States and other parts of the world, probably because of increased awareness, improved diagnostic means, and waning vaccine-induced immunity among adolescents and adults. Licensed vaccines do not kill the organism directly; the addition of a component inducing bactericidal antibodies would improve vaccine efficacy. We investigated Bordetella pertussis and Bordetella bronchiseptica LPS-derived core oligosaccharide (OS) protein conjugates for their immunogenicity in mice. B. pertussis and B. bronchiseptica core OS were bound to aminooxylated BSA via their terminal Kdo residues. The two conjugates induced similar anti-B. pertussis LPS IgG levels in mice. B. bronchiseptica was investigated because it is easier to grow than B. pertussis. Using B. bronchiseptica genetically modified strains deficient in the O-specific polysaccharide, we isolated fractions of core OS with one to five repeats of the terminal trisaccharide, having at the nonreducing end a GlcNAc or GalNAc, and bound them to BSA at different densities. The highest antibody levels in mice were elicited by conjugates containing an average of 8-17 OS chains per protein and with one repeat of the terminal trisaccharide. Conjugate-induced antisera were bactericidal against B. pertussis, and the titers correlated with ELISA-measured antibody levels (r = 0.74). Such conjugates are easy to prepare and standardize; added to a recombinant pertussis toxoid, they may induce antibacterial and antitoxin immunity.     

Tos ferina en lactantes y niños bien vacunados. ¿Son necesarias nuevas estrategias de vacunación?

Objective

To analyse the vaccination status of children diagnosed with pertussis and to compare the clinical manifestations of fully vaccinated with unvaccinated, or incompletely-vaccinated, children.

Methods

The clinical histories and vaccination cards of patients under 16 years of age seen in the Emergency Room of the University Hospital Vall d’Hebron, Barcelona (Spain), for pertussis confirmed by a microbiological study were reviewed. The study period lasted from January 1, 2009 to December 31, 2011.

Results

Two hundred and twelve cases were studied: 35 in 2009, 28 in 2010 and 149 in 2011. RT-PCR was positive in 210 patients, and 73 had a positive culture. Infants under 6 months of age account for 36.8% of all cases. Forty-four patients (21.5%) were not vaccinated. Forty-four (21.5%) children were between 2 and 5 months of age and had received 1-2 vaccine doses. One hundred and seventeen (57%) children were fully vaccinated; 76.9% (90 cases) had received the last dose less than 4 years ago. When clinical manifestations of the fully vaccinated patients were compared with those of the non-vaccinated or incompletely-vaccinated children, only cyanosis was found with a higher frequency in the latter group (P < .001). The age-adjusted probability of hospitalisation was significantly associated with non-vaccination (P = .001). The case mortality rate among inpatients was 1.3%.

Conclusions

The number of pertussis cases seen in our centre has risen significantly in the last year. More than half (57%) of the patients were fully vaccinated, and 76.9% had received the last dose in the previous 4 years. Other vaccination strategies, such as vaccination of adolescents, adults, and pregnant women, as well as a cocoon strategy are required to protect infants under 6 months of age. More effective vaccines need to be developed.     

Patterns of susceptibility in an outbreak of Bordetella pertussis: Evidence from a community-based study.

OBJECTIVE: To describe an outbreak of Bordetella pertussis and to assess which factors were associated with the development of clinical pertussis in children and adults during the outbreak. DESIGN: A case series was described to define the epidemiology of the pertussis outbreak. A school-based survey of children was used to measure the incidence of clinical pertussis over the previous six months. Vaccination records from the local public health facility were used to look at the relationship between age and vaccination parameters, and susceptibility to clinically diagnosed pertussis. A cross-sectional survey of teachers, parents and some hospital workers was used to assess these associations in adults. SETTING: An outbreak of pertussis in an isolated northern community in British Columbia. POPULATION STUDIED: All children in the community who attend daycare, kindergarten or school, and their parents were surveyed. In addition, some health care workers and mothers of preschool children were surveyed. MAIN RESULTS: A total of 31 suspected cases of pertussis were identified over a three-month period. Ninety per cent of the affected children who had available vaccination records had received four or five doses of pertussis vaccine. Sixty per cent of the town's 209 children returned completed surveys. Of these, 69% had available vaccination records. Thirty-six children (28%) reported symptoms that fit the case definition for pertussis over the previous three months. Attack rates were highest for the group of children aged 10 to 14 years. In a multivariate logistic regression analysis, receiving prophylactic medication and an increased number of years from the last vaccine dose were found to be significant predictors for developing pertussis. Thirty-four per cent of the estimated 291 adults in the community returned completed surveys. The attack rate of pertussis in the adults was only 9%. Being a member of the school staff and/or having a household contact with pertussis were significant predictors of developing pertussis. CONCLUSIONS: Immunity to pertussis appears to wane during childhood. Peak susceptibility appears to be during early adolescence. Adults do not seem to be at greater risk than adolescents for developing the disease, but it seems unlikely that this is due to better immunity. Rather, it is probably related to a lower risk of exposure to pertussis and a lower rate of progression to symptomatic disease when adults are infected.