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Seroprevalence of Antibodies to Pertussis Toxin among Different Age Groups in Thailand after 37 Years of Universal Whole-Cell Pertussis Vaccination

Friday, 22nd of April 2016

Seroprevalence of Antibodies to Pertussis Toxin among Different Age Groups in Thailand after 37 Years of Universal Whole-Cell Pertussis Vaccination

Nasamon Wanlapakorn et al. 

Excerpt below; full text is at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0148338

Abstract

Despite the high coverage of prophylactic vaccine against Bordetella pertussis infection in many countries for more than three decades, pertussis remains a common vaccine-preventable disease. Infections have been detected more commonly in countries using acellular pertussis vaccine in their Expanded Program of Immunization. Thailand implemented a routine infant immunization program with whole-cell pertussis vaccine in 1977, and since 1992, the national vaccine policy has offered a five-dose whole-cell pertussis vaccine for children given at the ages of 2, 4, 6, 18, and 48 months. This study aimed to investigate the seroprevalence of antibodies to pertussis toxin among healthy people across all ages to determine the level of whole-cell vaccine-induced immunity in the population, and to identify which age group should be targeted for a booster dose. The lowest seronegative rate and highest geometric mean concentrations were found in the 0–10 years age group, corresponding to their recent pertussis vaccination. The proportion of people with undetectable IgG level was prominent, starting after 11 years of age onwards. Now that a reduced-dose pertussis vaccine with fewer adverse effects is available, a booster dose during adolescence should be considered in order to reduce the incidence of pertussis disease. Further studies exploring how long the reduced-dose pertussis vaccine can provide protective immunity against pertussis disease when administered to adults and adolescents should also be performed.

 

Citation: Wanlapakorn N, Ngaovithunvong V, Thongmee T, Vichaiwattana P, Vongpunsawad S, Poovorawan Y (2016) Seroprevalence of Antibodies to Pertussis Toxin among Different Age Groups in Thailand after 37 Years of Universal Whole-Cell Pertussis Vaccination. PLoS ONE 11(2): e0148338. doi:10.1371/journal.pone.0148338

Introduction

Pertussis is a contagious bacterial disease of the respiratory tract characterized by a severe protracted paroxysmal cough that sometimes ends with a whooping sound, also known as “whooping cough.” It is caused mainly by Bordetella pertussis and is spread by direct contact with or breathing the aerosolized secretions of infected individuals. In adolescents and adults, the classic symptom of pertussis is a prolonged cough for 6–10 weeks, whereas in infants younger than 6 months, clinical manifestations are short catarrhal stage, gagging, cyanosis, apnea, or respiratory failure without whooping [1]. Despite the high coverage of prophylactic vaccine in many countries, B. pertussis infection remains a common vaccine-preventable disease and accounts for 139,786 cases reported worldwide in 2014 [2]. In the United States, the Centers for Disease Control and Prevention reported 28,660 cases and 9 deaths from pertussis in 2014, of which the majority (7/9; 77.8%) of the fatal cases were infants younger than 3 months of age [3].

Whole-cell pertussis (wP) vaccines consist of suspensions of the entire B. pertussis organism that has been inactivated. This type of vaccine was first licensed as part of routine infant vaccination in the United States in the mid-1940s, [4] and many countries have implemented this vaccine into their Expanded Program of Immunization (EPI). Although the vaccine was proven to be effective because the morbidity and mortality from pertussis disease decreased after its implementation in many countries, it was associated with several adverse local and systemic reactions, such as pain, redness and swelling at injection sites, high-grade fever, hypotonic–hyporesponsive episodes, and seizures [5]. In the 1980s, the acellular pertussis (aP) vaccine was introduced, which has also proven to be effective with fewer adverse effects. Therefore, many industrialized countries changed from the wP to the aP vaccine. However, head to head studies on the long-term efficacy of the wP and aP vaccines with regards to their efficacy in preventing the disease rather than their ability to induce antibody titers in vaccinees are limited.

Despite the high coverage of pertussis vaccine worldwide for many years, the incidence of pertussis has gradually increased. Recent research found that the waning of vaccine-induced pertussis immunity is one of the major contributing factors to pertussis disease [6,7]. Moreover, a woman who does not have protective anti-pertussis antibodies cannot pass the protection to her child during pregnancy, thus the newborn infant is susceptible to the disease. In this age group, pertussis may be severe and life-threatening [8].

Thailand implemented a routine infant immunization program with two doses of the diphtheria–tetanus toxoid–whole-cell pertussis (DTP) vaccine for all infants in 1977 [9], and this recommendation was changed to three doses of DTP in 1982 and four doses (at 2, 4, 6, and 18 months) in 1987. Since 1992, the national vaccine policy in Thailand has used five doses of DTP vaccine for children at the ages of 2, 4, 6, 18, and 48 months. Although many countries recommended a tetanus–diphtheria–acellular (Tdap) pertussis vaccine booster during adolescence [10–11], Thailand continued to use the whole-cell pertussis vaccine and integrated only the diphtheria–tetanus vaccine into its EPI for this age group and adults [12]. Although the number of pertussis cases from passive surveillance in Thailand was quite low between 2009 and 2014 (ranging from 0.01 to 0.11 cases per 100,000 population) with no report of major outbreaks [13–14], these numbers are likely to be underestimated because of inadequate disease surveillance and limited laboratory confirmation of suspected cases. The current laboratory diagnostic test for B. pertussis infection performed by The Ministry of Public Health for all hospitals in Thailand is the real-time polymerase chain reaction. In general, only specimens from clinically suspected cases or from a presumed outbreak would be collected and laboratory-tested.

To explore the serological profiles of anti-pertussis toxin IgG in a cohort of Thais who received only the wP vaccine in the past 37 years, we conducted a seroepidemiology survey to determine the antibody level across all ages. The results could help determine the level of wP vaccine-induced immunity and identify which age group should be targeted for a booster dose.