Modeling rates of infection with transient maternal antibodies and waning active immunity: application to Bordetella pertussis in Sweden.

Serological surveys provide reliable information from which to calculate forces (instantaneous rates) of infection, but waning immunity and clinical consequences that depend on residual immunity complicate interpretation of results. We devised a means of calculating these rates that accounts for passively acquired maternal antibodies that decay or active immunity that wanes, permitting re-infection. We applied our method to pertussis (whooping cough) in Sweden, where vaccination was discontinued from 1979 to 1995. A national cross-sectional serosurvey of antibodies to pertussis toxin, which peak soon after infection and then decay, was conducted shortly after vaccination resumed. Together with age-specific contact rates in Finland, contemporary forces of infection enable us to evaluate the recent assertion that the probability of infection upon contact is age-independent. We find elevated probabilities among children, adolescents and young adults, whose contacts may be more intimate than others. Products of contact rates and probabilities of infection permit transmission modeling and estimation of the intrinsic reproduction number. In contrast to another recent estimate, ours approximates the ratio of life expectancy and age at first infection. Our framework is sufficiently general to accommodate more realistic sojourn distributions and additional lifetime infections.

[Polio close to eradication]. / Polio närmar sig utrotning.

Polio close to eradication The WHO Global Polio Eradication Initiative has been highly successful. With a dramatic decrease in polio since it started in 1988, the number of globally reported cases reached a record low of 37 in 2016. This article describes the WHO Endgame Strategic Plan including milestones that have been reached and challenges that have to be overcome in order to reach the goal of polio eradication by 2020. Efforts to strengthen immunizations systems and to detect and interrupt polio virus transmission focus on the three remaining endemic countries, namely Pakistan, Afghanistan and Nigeria. In 2016 the WHO took the first step to withdraw the oral polio vaccine (OPV) by globally shifting from trivalent to bivalent OPV.  The role of the inactivated vaccine (IPV) in the final phase of eradication and in the post-eradication situation is also considered. Certification of eradication and containment of all polio virus by the end of 2020 is a key objective. Legacy planning includes mainstreaming polio functions into ongoing public health programmes.

Long-term follow-up of Swedish children vaccinated with acellular pertussis vaccines at 3, 5, and 12 months of age indicates the need for a booster dose at 5 to 7 years of age.

OBJECTIVES: The purpose of this work was to evaluate the long-term effectiveness of vaccination with acellular pertussis vaccines at 3, 5, and 12 months of age. METHODS: Clinical follow-up of reported culture- and polymerase chain reaction-confirmed cases of pertussis was initiated during October 1997 in most of Sweden (except Gothenburg and environs). The study population included 90% of Swedish children born during 1996 or later (ie, who received diphtheria-tetanus-acellular pertussis vaccines at 3, 5, and 12 months of age) and children who had participated in a large pertussis vaccine trial in 1993-1996. Age-specific incidences were estimated using reported culture- or polymerase chain reaction-confirmed pertussis from October 1997 to September 2004 in areas covered by enhanced surveillance. In addition, annual overall and age-specific incidences of pertussis throughout Sweden before and after introduction of acellular pertussis vaccines were estimated. RESULTS: The overall incidence of notified culture- and polymerase chain reaction-confirmed pertussis dropped from 113 to 150 per 100,000 during 1992-1995 to 11 to 16 per 100,000 during 2001-2004. In areas of enhanced surveillance, the incidence of pertussis was 31 per 100,000 person-years after 2 doses and 19 per 100,000 person-years after the third dose at 12 months of age. The age-specific incidence remained low for approximately 5 years after the third dose but increased in children aged 6 to 8 years, becoming 32 and 48 per 100,000 person-years, respectively. The highest incidence occurred among infants who were unvaccinated or had received only 1 dose of diphtheria-tetanus-acellular pertussis vaccine. CONCLUSIONS: The increased incidence among 7- to 8-year-olds (ie, mainly acellular pertussis vaccine-vaccinated children) suggests waning of vaccine-induced protection from pertussis. Along with a concomitant increase in incidence among infants, most likely infected by older siblings, these data suggest a booster dose of acellular pertussis vaccine is warranted from 5 to 7 years of age.

Low levels of antipertussis antibodies plus lack of history of pertussis correlate with susceptibility after household exposure to Bordetella pertussis.

Prospectively collected data in a Swedish vaccine efficacy trial were used to investigate transmission of pertussis from small study infants to other household members. Forty one percent (258/627) of the exposed persons with paired serology had laboratory confirmed pertussis. The majority of those with laboratory confirmed pertussis had less than 14 days of cough and many were asymptomatic. High susceptibility to symptomatic pertussis was found among persons with low initial IgG antibody concentrations against pertussis toxin, especially those without previous history of pertussis vaccination or disease.

Vaccinovigilance in Europe--need for timeliness, standardization and resources.

OBJECTIVE: To identify gaps in the systems for reporting adverse events following immunization (AEFI) in Europe by means of an interactive database constructed using a standardized approach. METHODS: A comparative survey was conducted in 1999-2000, using structured questionnaires addressed to the government authorities responsible for national immunization programmes and drug safety surveillance in all European Union (EU) Member States and in Norway and Switzerland. FINDINGS: The reporting of adverse vaccine reactions (AVRs) is covered by regulations in 13 of the 17 countries. Four countries have a specialized expert group with responsibility for vaccine safety. Only six professionals work full-time on vaccine safety in the 17 countries; in four of these countries the person is medically qualified. Fourteen countries have centralized reporting systems; in 14 countries the responsible authority is the drug regulatory agency. AEFI are reported using the procedure used for adverse drug reactions (ADRs) in all except four countries. The reporting form is not usually designed for vaccines and important details may therefore not be requested. Clinical definitions for vaccine reactions are not available. Twelve countries have appropriate official definitions for events or reactions, but the list of reportable events varies considerably between countries. The assessment of adverse vaccine reactions (AVRs) is hampered by lack of exact denominator data. Feedback to the rapporteurs was provided in 13 countries, but its quality was highly variable. CONCLUSION: The database facilitated a simple comparison of vaccinovigilance systems across participating countries. Most of the problems identified related to the reporting and analysis of AEFI could be solved through standardization and intensified international collaboration. On a national level, functional vaccinovigilance systems should be the shared responsibility of the drug regulatory authority and the national immunization programme. The resources for development and management of vaccine safety systems should be urgently improved.

Declining pertussis incidence in Sweden following the introduction of acellular pertussis vaccine.

Acellular pertussis vaccines were introduced nation-wide in Sweden in 1996, 17 years after the withdrawal of whole-cell pertussis vaccine from the childhood immunisation schedule. We report national data on age specific incidence of culture-confirmed Bordetella pertussis for 1986-2000, and clinical follow-up for 3 years (October 1997-September 2000) in children born in 1996-2000 and from children born in 1993-1994 who had participated in a trial of pertussis vaccines. The annual incidence of culture-confirmed B. pertussis was 89-150 per 100,000 before introduction of acellular pertussis vaccines and has dropped to 17-26 per 100,000. The data suggest that unimmunised infants and children who have received only one dose of pertussis vaccine were provided some protection. The decline is most obvious from the second dose onwards and remained stable for 4-5 years after the third dose in the absence of any booster dose. The first signs of waning immunity were observed at 6-7 years of age in the trial cohort. The short-term benefits reflect high vaccination coverage and high initial efficacy. The full impact of the acellular pertussis vaccination programme in infants remains to be established.