The global burden of measles in the year 2000--a model that uses country-specific indicators

The estimation of the global burden of measles is challenging in the absence of reliable and comparable surveillance systems worldwide. A static model is described that enables estimation of measles morbidity, mortality, and disability for the year 2000 on the basis of country-specific information (i.e., demographic profile, vaccine coverage, and estimates of case-fatality ratios). This approach estimated a global incidence of 39.9 million measles cases, 777,000 deaths, and 28 million disability-adjusted life years. The World Health Organization regions of Africa and Southeast Asia had 70% of incident cases and 84% of measles-related deaths; 11 countries alone (Afghanistan, Burkina Faso, Democratic Republic of the Congo, Ethiopia, India, Indonesia, Niger, Nigeria, Pakistan, Somalia, Uganda) account for 66% of deaths. This approach quantifies the measles burden by considering country-specific indicators, which can be updated, permitting an assessment of country, regional, and global changes in the burden associated with measles infection.

Monitoring vaccine safety during measles mass immunization campaigns: clinical and programmatic issues

In the planning and implementation of mass immunization campaigns, vaccine delivery has always been a priority. However, safety issues have gained increasingly more attention and grown in importance, and campaign planners must now take them into prime consideration. The World Health Organization has released guidelines to assist with the design and implementation of safety surveillance systems, primarily for developing countries, and these include a new monograph for measles mass campaigns. Experience in the past decade with mass campaigns (primarily in developed countries) shows that measles vaccine performs in these settings as anticipated from pre- and post-licensure studies. Serious adverse events are rare, even under the increased scrutiny extended during a campaign. The experience in developing country settings is growing. The implementation of safety surveillance for mass campaigns offers a unique opportunity for countries to avoid crisis situations and to begin vaccine safety monitoring in routine immunization programs.

Safety of immunisation and adverse events following vaccination against hepatitis B

Hepatitis B vaccines (HBVs) are composed of highly purified preparations of hepatitis B virus surface antigen (HBsAg). An adjuvant, either aluminium phosphate or aluminium hydroxide, is added to the vaccines, which are sometimes preserved with thiomersal. In placebo-controlled studies, common side effects other than local reactions were reported no more frequently among vaccine recipients than among individuals receiving a placebo. A number of controversial adverse events have, however, been purported to be associated with HBVs, including rheumatoid arthritis (RA), diabetes, demyelinating diseases (e.g., multiple sclerosis [MS]), chronic fatigue syndrome, and more recently, lymphoblastic leukaemia. In addition, the safety of the thiomersal and aluminium contained in the vaccine has also been under close scrutiny. These issues have been reviewed by a number of country-specific or international independent review committees such as that of the US Institute of Medicine (IOM) and the World Health Organization's (WHO) Global Advisory Committee on Vaccine Safety (GACVS). Upon review of the scientific evidence, none of the serious allegations have so far been confirmed. On the contrary, scientific evidence has accumulated to disprove many of the allegations. In particular, the IOM committee has concluded that the evidence favoured rejection of a causal relationship between HBV administered to adults and incident MS or MS relapse. Whilst it is important to continue monitoring some of the safety issues, there is no evidence to suggest that the WHO should consider altering its recommendation that all countries should have universal infant and/or adolescent immunisation programmes. The risks of hepatitis B vaccination are only theoretical in comparison with clear benefits in terms of cirrhosis and cancer prevention, and the HBV remains one with an excellent safety profile.

Investigation into a cluster of infant deaths following immunization: evidence for methanol intoxication

A cluster of infant deaths due to severe metabolic acidosis following immunization was reported in a prosperous farming village in Egypt. Fears that more deaths might occur, and of a deleterious effect on national immunization programs prompted an urgent investigation by national and international partners. The deaths, and other previously unrecognized illness following immunization, were associated with excessive topical application of methanol. Methanol was employed as an anti-pyretic and anti-inflammatory agent following injections. Fear of adverse reactions to vaccine had encouraged increasing use of methanol for these purposes. Local physicians and nurses were unaware of the toxicity of methanol and did not consider it in the differential diagnosis, and thus did not offer appropriate life-saving therapy. The interaction of traditional practices and modern medical interventions can have clinically important consequences, and should be considered when programs are introduced and as they are monitored.

The Brighton Collaboration: addressing the need for standardized case definitions of adverse events following immunization (AEFI)

To further scientific progress of immunization safety, comparability of data from clinical trials and surveillance systems is essential. Comparability requires the availability of standardized case definitions for adverse events following immunization (AEFI) and guidelines for case determination, recording and data presentation.

METHOD

International collaborative working groups, consisting of professional volunteers from developed and developing countries, conduct systematic literature reviews to develop 50-100 AEFI definitions. Case definitions are finalized after a comment period by a reference group consisting of organizations concerned with immunization safety, and will be disseminated via the world-wide-web and other means for free world-wide use.

RESULTS

Literature reviews yielded substantial diversity in data collection and presentation. We have developed standardized case definitions together with guidelines for use in clinical trials and surveillance systems.

CONCLUSIONS

Diversity in safety methods leads to considerable loss of scientific information. We have built the necessary international network of currently about 300 participants from patient care, public health, scientific, pharmaceutical, regulatory and professional organizations to develop and assess standardized AEFI case definitions and guidelines. Evaluation studies, global implementation, ongoing definition development and a continuously growing network will be essential for the success of the collaboration.

Immunisation safety: a priority of the World Health Organization's Department of Vaccines and Biologicals

In 1999, the World Health Organization (WHO) Department of Vaccines and Biologicals launched the Immunisation Safety Priority Project to boost its activities in this area, with the aim of establishing a comprehensive system to ensure the safety of all immunisations given in national immunisation programmes. Countries are the primary focus of this project. The WHO has a role to play not only because of its technical and normative role but also because of its privileged relationship with country authorities and other partners, its global vision and mandate, and because it is perceived as free from conflicts of interest. There are four areas of focus in the project: quality control and assessment tools to ensure vaccine safety from clinical trials up to and including the point of use;research and development of safer and simpler delivery systems; access to safer and more efficient systems for vaccine delivery and sharps waste management; and mechanisms to respond promptly and effectively to vaccine safety concerns. The project emphasises the importance of advocating safety and developing necessary infrastructure and human resource to properly deal with immunisation related safety issues at a national level.

Ensuring vaccine safety in immunization programmes--a WHO perspective

Ever since vaccines were firstly used against smallpox, adverse events following immunization have been reported. As immunization programmes expand to reach even the most remote communities in the poorest countries, it is likely that many more events will be temporally linked with vaccine administration. Furthermore, the profound shift in the general public and media interest in adverse events may lead to undue concerns and allegations which may ultimately jeopardize immunization programmes world-wide. While the health professional has understood this issue for some time, the public and the media have now also become all too aware of the significance of vaccine-related adverse events. The familiar vaccines, well-tested over decades, have not changed--but the perception regarding their safety has shifted. Claims outrageous or reasonable are being made against both the old and the newly-introduced vaccines. At the same time, the immunological and genetic revolution of the last decade may well bring to our notice some hypothetical risks that need to be addressed at pre-clinical level. WHO has been at the leading edge to guarantee vaccine safety for the last 30 years and will continue to do so. The Organization's plans for the next decade and beyond include the Safe Injection Global Network (SIGN), the development and introduction of safer technologies, and the prevention, early detection and management of AEFIs. The new technologies include needle-containing injection devices such as the autodisable syringe, as well as mucosal and transcutaneous immunization. Training will continue to be at the centre of WHO's efforts, limiting human error to a minimum. Mechanisms have been set in place to detect and respond to new and unforeseen events occurring. Above all, there is a willingness to respond to new climates and new technologies so that the Organization is in the best position to ensure safe immunization for all the world's children.

The Immunization Monitoring Program Active (IMPACT) prospective five year study of Canadian children hospitalized for chickenpox or an associated complication

BACKGROUND

Varicella vaccine was approved for use in Canada in 1998. A major goal of universal varicella vaccine programs is to reduce severe infection and associated complications. Baseline data are essential against which to judge the effectiveness of routine childhood immunization.

OBJECTIVE

To describe morbidity and mortality among children hospitalized for chickenpox. Methods. From January 1, 1991, to March 31, 1996, chickenpox admissions to 11 pediatric referral centers were actively identified. Patient and illness characteristics were compared for 3 subgroups defined by prior health: healthy; unhealthy but immunocompetent; immunocompromised.

RESULTS

Of 861 cases 488 (56.7%) were healthy, 75(8.7%) were unhealthy and 298 (34.6%) were immunocompromised. The immunocompromised children differed from healthy/unhealthy cases in mean age (6.4 vs. 4.0/4.6 years, respectively, P < 0.0001); median interval from rash onset to admission (2 vs. 5/5 days, P < 0.0001); complication rate (20% vs. 90%/79%; P = 0.001); and rate of acyclovir therapy (98% vs. 24%/39%; P = 0.001). Unhealthy vs. healthy cases had a higher frequency (P < 0.01) of intensive care (13.3% vs. 4.7%), ventilation (9.3% vs. 2.0%) and death (4% vs. 0.2%).

CONCLUSION

These data provide a baseline for morbidity/mortality resulting from chickenpox before varicella vaccine use in Canada.

Developing a national system for dealing with adverse events following immunization

Although vaccines are among the safest of pharmaceuticals, the occasional severe adverse event or cluster of adverse events associated with their use may rapidly become a serious threat to public health. It is essential that national monitoring and reporting systems for vaccine safety are efficient and adequately coordinated with those that conventionally deal with non-vaccine pharmaceuticals. Equally important is the need for an enlightened and informed national system to be in place to deal with public concerns and rapid evaluation of the risk to public safety when adverse events occur. Described in this article is the outcome of efforts by the WHO Global Training Network to describe a simple national system for dealing with vaccine safety and with emergencies as they arise. The goals of a training programme designed to help develop such a system are also outlined.

Epidemiological features of pertussis in hospitalized patients in Canada, 1991-1997: report of the Immunization Monitoring Program--Active (IMPACT)

To assess the morbidity associated with the continued high levels of pertussis, we studied all children <2 years of age who were admitted to the 11 Immunization Monitoring Program--Active (IMPACT) centers, which constitute 85% of Canada's tertiary care pediatric beds. In the 7 years preceding implementation of acellular pertussis vaccine, a total of 1,082 pertussis cases were reported, of which 49.1% were culture-confirmed. The median age of the patients was 12.4 weeks; 78.9% of cases were in children <6 months of age. Complications of pertussis were common: pneumonia was reported in 9.4% of cases, new seizures in 2.3%, and encephalopathy in 0.5%. There were 10 deaths (0.9%), all in children < or =6 months of age. Duration of hospitalization was longer (9.3 days vs. 4.9 days; P = .001) and intensive care was required more frequently (19.2% vs. 4.9%; P = .001) in infants under <6 months of age than in those > or =6 months. Pertussis continues to cause significant morbidity and occasional mortality in Canada, particularly in young infants.

A single dose of an effective whole cell pertussis vaccine does not significantly increase protection in children primed with a less effective vaccine

We evaluated if a single dose of a protective whole cell pertussis vaccine given before school entry to children primed with a less effective vaccine would increase their protection. A school cohort including 3876 students and a family cohort including 162 children were assessed. Although there was a trend toward increased protection. the better vaccine did not provide a significant improvement. These results suggest that a single dose of an effective vaccine given to children primed with a less effective one does not raise the protection to at level similar to that provided by three doses of the better vaccine.

Measles in adults in Canada and the United States: implications for measles elimination and eradication

BACKGROUND

Despite the implementation of mass school catch-up campaigns for measles in Canada, an outbreak of measles occurred in early 1997 mostly affecting the adult population. The higher incidence in Canada in adults led us to compare immunization policies and the evolution of measles among adults in Canada and the US.

METHODS

Based on information gathered from both national immunization programmes and surveillance systems.

RESULTS

Although the proportion of cases occurring in adults has increased tremendously in both countries in the past decade, there was no increase in measles incidence in these populations. The most likely factors to explain the higher rate of measles occurring in adults in Canada are the younger age at administration of first dose in Canada, the delay in implementation of a second dose policy in Canada compared with the US combined with the lack of prematriculation immunization requirements in Canadian colleges and universities, and the higher rate of overseas travel to and from Canada. The situation in Canada may also have been exacerbated by incomplete efforts to control measles for many years without attempting to eliminate the disease.

CONCLUSIONS

In order to prevent measles in adults, high-risk groups must be identified and catch-up for selected groups considered. Vaccination of international travellers to endemic areas should be recommended until global elimination has been achieved. Appropriate measles control strategies in younger populations seem to be effective in preventing measles in adults. The experience in Canada and the US suggests that measles transmission in adults is unlikely to be a major impediment to regional elimination or global eradication.

Evaluation of the promotional materials used during the measles mass immunization campaign in Ontario and British Columbia

OBJECTIVE

To evaluate the promotional materials used during measles mass immunization campaign.

DESIGN

A telephone survey was conducted among parents of targeted children in Ontario and British Columbia (BC).

RESULTS

The leaflet distributed at school was considered to be the most useful source of information for 79% and 69% of the parents of school-aged children in Ontario and BC, respectively. Newspaper articles (27%) and information obtained through public health nurses (24%) were the most appreciated sources of information for the parents of preschoolers only. There was a notable increase in the proportion of parents who considered measles immunization important as well as those who had concerns about measles immunization at the time of the interview compared with the period before the mass campaign.

CONCLUSION

The leaflet distributed at school (for parents of school-aged children) and newspaper articles and information obtained from public health nurses (for the parents of preschoolers only) were found to be the most useful sources of information.

Measles vaccines: a review of adverse events

A great deal of controversy has recently been generated over the publication of several articles implicating measles vaccine in the induction of Crohn's disease and autism. The publication of this work has already had a negative impact on measles vaccine acceptance in the UK. These allegations are particularly troubling because they arise in the context of increased use of measles vaccine as global control of measles nears and the international community considers strategies for a drive towards eradication. In 1994, the US Institute of Medicine reviewed the world literature and published a comprehensive review of adverse events associated with measles-containing vaccines. Reviewing the literature published between 1994 and the present day, reveals that there is considerable new data suggesting that modified gelatin rather than egg proteins is responsible for most episodes of anaphylaxis following measles vaccination. New work weakens the possible links between measles vaccine and subacute sclerosing panencephalitis and Guillain-Barré syndrome, but strengthens the rare association of measles-containing vaccines with post infectious encephalomyelitis. The alleged associations between measles vaccination and Crohn's disease and autism are based upon weak science and have largely been refuted by a large volume of stronger work. A review of the data generated in the last 4 years amply demonstrates the continued efforts of the scientific community to monitor and understand true measles vaccine-associated adverse events. The rapidity and clarity of this same community's debunking of the spurious associations with Crohn's disease and autism suggests that those charged with vaccination programmes have learned from past mistakes. During 30 years of worldwide use, measles vaccination has proven to be one of the safest and most successful health interventions in the history of mankind. It is not a 'perfect' vaccine, but the benefits of measles vaccination far outweigh the risks even in countries with low incidence of measles and high rates of measles vaccine coverage.

Evaluation of the promotional materials used during the measles mass immunization campaign in Ontario and British Columbia

OBJECTIVE

To evaluate the promotional materials used during measles mass immunization campaign.

DESIGN

A telephone survey was conducted among parents of targeted children in Ontario and British Columbia (BC).

RESULTS

The leaflet distributed at school was considered to be the most useful source of information for 79% and 69% of the parents of school-aged children in Ontario and BC, respectively. Newspaper articles (27%) and information obtained through public health nurses (24%) were the most appreciated sources of information for the parents of preschoolers only. There was a notable increase in the proportion of parents who considered measles immunization important as well as those who had concerns about measles immunization at the time of the interview compared with the period before the mass campaign.

CONCLUSION

The leaflet distributed at school (for parents of school-aged children) and newspaper articles and information obtained from public health nurses (for the parents of preschoolers only) were found to be the most useful sources of information.

A benefit-cost analysis of two-dose measles immunization in Canada

In 1992, because of the limitations of the one-dose measles immunization program, the National Advisory Committee on Immunization (NACI) recommended a two-dose measles immunization program to eliminate measles. More recently, NACI recommended also a special catch-up program to prevent predicted measles outbreaks and to achieve an earlier elimination of measles. The objective of this study was to complete a benefit-cost analysis of a two-dose immunization program with and without a mass catch-up compaign compared with the current one-dose program. The resulting benefit: cost ratios vary between 2.61:1 and 4.31:1 depending on the strategy used and the age of the children targeted. Given the parameters established for this analysis, the benefits of a second-dose vaccination program against measles far outweight the costs of such a program under all scenarios.

Modelling the incidence of measles in Canada: an assessment of the options for vaccination policy

A range of vaccination policy options for improving the control of measles in Canada is investigated using a mathematical model to simulate transmission of the disease. Results suggest that a catch up campaign giving a second dose of vaccine to children aged up to 18 years would have an immediate impact on transmission, which could be maintained by the introduction of a routine second dose at either 18 months or 5 years of age. Introducing a routine second dose of vaccine without a catch up campaign would allow continued endemic transmission of measles among older children for at least 10-15 years.

Reporting vaccine-associated adverse events

OBJECTIVE

To determine family physicians' awareness of the need to monitor and report vaccine-associated adverse events (VAAE) in Canada and to identify mechanisms that could facilitate reporting.

DESIGN

Mailed survey.

SETTING

Canadian family practices.

PARTICIPANTS

Random sample of 747 family physicians. Overall response rate was 32% (226 of 717 eligible physicians).

MAIN OUTCOME MEASURES

Access to education on VAAE; knowledge about VAAE monitoring systems, reporting criteria, and reporting forms; method of reporting VAAEs and reasons for not reporting them; and current experience with VAAEs.

RESULTS

Of 226 respondents, 55% reported observing VAAEs, and 42% reported the event. Fewer than 50% were aware of a monitoring system for VAAE, and only 39% had had VAAE-related education during medical training. Only 28% knew the reporting criteria. Reporting was significantly associated with knowledge of VAAE monitoring systems and reporting criteria (P < 0.01).

CONCLUSION

Physicians need more feedback and education on VAAE reporting and more information about the importance of reporting and about reporting criteria and methods.

Vaccination coverage levels among children two years of age and selected aspects of vaccination practices in Canada - 1996

OBJECTIVE

To obtain population-based estimates of coverage for routine childhood vaccinations at two years of age and information about selected aspects of vaccination practices in Canada.

METHODS

Data were collected through a mail survey of a sample of households with two-year-olds born between February 1993 and January 1994. To obtain population estimates, survey data were weighted to match known population distributions of geographic region, community size, household income level and single-parent versus two-parent family type.

RESULTS

Up-to-date vaccination coverage was estimated as 84.8% (95% CI 82.0 to 87.3) for diphtheria-pertussis-tetanus vaccine, 89.9% (95% CI 87.4 to 92.0) for polio vaccine, 93.3% (95% CI 91.2 to 95.0) for measlesmumps-rubella vaccine and 69.3% (95% CI 65.8 to 72.6) for Hae-mophilus influenzae type b vaccine. Less than one per cent of children had not received vaccination of any kind. Ninety-five per cent of parents cited the benefits of vaccination as a reason for having their children vaccinated.

CONCLUSION

Coverage levels indicate that the national targets set for 1997 for up-to-date vaccination of children at two years of age have been reached for mumps and rubella, and good progress isbeing made towards targets for the remaining vaccines. Special attention from providers and parents is required to prevent vaccination delays, particularly for 18-month booster doses.

Estimates of the effectiveness of a whole-cell pertussis vaccine from an outbreak in an immunized population

Pertussis has re-emerged as a public health problem in Canada in recent years, emphasizing concerns about the effectiveness of the currently licensed whole-cell vaccine. Following a 1994 outbreak in Nova Scotia, we conducted a case-control study of 483 children aged < 10 years to assess vaccine effectiveness. Ninety-three percent of children aged 6 months and above had received three or more doses of vaccine, however, only 78% had received age-appropriate immunization. Among children aged 4 years and more, vaccine effectiveness against laboratory-confirmed pertussis was 57% (95% CI, 23-77%) for age-appropriate immunization (five doses) vs partial or no immunization. Vaccine effectiveness increased with increasing number of doses from 25% (95% CI, -58-65%) for three or more doses to 55% (95% CI, -15-83%) for five doses, compared with 0-2 doses.

Vaccination coverage of 2-year-old children and immunization practices--Canada, 1994

The purpose of the study was to assess vaccination coverage of 2-year-olds and estimate immunization practices in Canada using a postal survey with a panel of 862 households. RIM weighting was used to provide national estimates. 95% CIs were calculated using the binomial method. Completed questionnaires were received for 534 children born between February 1991 and January 1992. Thirty nine percent of children had received all/most of their vaccinations at a public health clinic. Overall 5.6% parents indicated they had their child immunized because it was mandatory and 7.4% because of requirements for school, pre-school, nursery or day care attendance. A total of 78.7% of parents remembered receiving information on benefits of immunizations and 97% on the risks/side-effects. By their second birthday, 83.7% (95% CI 80.3-86.7) of 2-year-olds had received complete immunization against poliomyelitis; 97.2% (95% CI 95.4-98.4), at least one dose of a measles containing vaccine; 86.5% (95% CI 83.3-89.3), at least one dose of Haemophilus influenzae type b vaccine; and 81.6% (95% CI 78.1-84.8), at least, four doses of diphtheria, tetanus and pertussis vaccine.

Rubella reimmunization: comparative analysis of the immunoglobulin G response to rubella virus vaccine in previously seronegative and seropositive individuals

Rubella virus (RV)-specific immunoglobulin G (IgG) antibodies were studied in military recruits undergoing unselected immunization with live attenuated measles, mumps, and rubella virus (MMR) vaccine. Three different whole-RV enzyme immunoassays (EIAs) and an epitope-specific EIA with a synthetic peptide (BCH-178c) representing a heutralization domain on the RV E1 envelope protein were used. Before vaccination, 84.2, 87.7, and 84.5% of the subjects tested (n = 399) were found to be seropositive (> 10 IU/ml or assay equivalent) by the three whole-RV EIAs, respectively, while only 82.5% were seropositive by the BCH-178c EIA. Although prevaccination seropositivity rates were similar for the whole-RV EIAs (sensitivity, 94 to 100%), many sera considered seropositive by the whole-RV EIAs had E1 peptide EIA antibody levels of < 10 IU/ml (sensitivity, 77.4 to 80.7%). One month after vaccination, 97.8, 97.2, and 93.5% of the subjects who were followed (n = 356) were seropositive by the three whole-RV EIAs, respectively, while 89% had BCH-178c peptide-specific IgG titers of > 10 IU/ml. After vaccination, depending on the assay used, up to 20.6% of initially seropositive individuals exhibited a greater than fourfold increase in RV-specific IgG, while up to 47.3% showed a greater than twofold increase. Increased antibody titers after vaccination (seroboosting) were most frequently associated with low levels of BCH-178c peptide-specific IgG before vaccination. RV protein-specific IgG was also studied by immunoblot assays in a subset (n = 56) of individuals receiving the MMR vaccine. Of these, 89.4 and 91.1% exhibited RV protein (E1, E2, and C protein)-specific IgG before and after vaccination, respectively. Seroboosting (two- to fourfold increase in EIA titers of individuals seropositive by the whole-RV EIA before vaccination) was usually accompanied by a shift in the IgG immunoblot pattern from a single (E1) to multiple (E1-E1, E1-C, or E1-E2-C) specificities, suggesting exposure of new epitopes as a result of viral replication.

Seroprevalence of measles- and rubella-specific antibodies among military recruits, Canada, 1991

A study of the seroprevalence of measles- and rubella-specific antibodies among military recruits in Canada in 1991 was undertaken to: 1) determine the proportion of military recruits who are measles and/or rubella seropositive when they enter the military; 2) detect general problems in the immune coverage in the young adult population; and 3) determine the proportion of measles seronegativity attributable to non-response, waning immunity or lack of exposure to either the disease or the vaccine. One initial blood sample was collected from all 399 recruits enrolled in basic training during the month of January 1991, prior to immunization with measles-mumps-rubella vaccine (MMR). Another sample was obtained from 354 of these recruits 3 to 5 weeks following this immunization. Only 18 (4.5%) recruits had negative measles-specific neutralization on the first sample. Only 12 (3.0%) recruits had negative measles-specific EIA on the first sample. All recruits had neutralization titres 40 or higher on the second sample. A total of 43 (10.8%) individuals had negative results for rubella EIA before immunization, 35 of which (81.4%) tested positive on the second sample.

Incidence of Guillain-Barré syndrome in Ontario and Quebec, 1983-1989, using hospital service databases

To determine the incidence of Guillain-Barré syndrome (GBS) in the Canadian provinces of Ontario and Quebec during 1983-1989 and to demonstrate the feasibility of measuring the incidence of GBS through internal record linkage of Canadian hospital service data, we conducted a record linkage study. This study used the databases of the Hospital Medical Records Institute and the Ministère de la santé et des services sociaux du Québec. We extracted records containing the International Classification of Diseases, 9th revision, code for GBS or a diagnosis likely to harbor misclassified GBS cases from each database and linked them internally using computerized algorithms. We identified a total of 1,302 and 1,031 incident cases of GBS admitted to Ontario and Quebec hospitals, respectively. The calculated mean annual GBS incidence rate in each province, after age and sex standardization to the 1986 Canadian census population, was 2.02 per 100,000 person-years in Ontario and 2.30 per 100,000 person-years in Quebec. Chart reviews revealed that the false-positive diagnosis rate might be as high as 0.26 per 100,000 person-years in Ontario and 0.21 per 100,000 person-years in Quebec. With adjustment for these false-positive rates, the incidence rate of GBS becomes 1.51 per 100,000 person-years and 1.78 per 100,000 person-years in Ontario and Quebec, respectively. In both provinces, the incidence rate was higher in older age strata (70-80 years) and in males. We saw no seasonal or geographic pattern.

[Surveillance of secondary effects of vaccination]

Although modern vaccines are usually well tolerated and efficacious, no vaccine is totally safe nor totally efficacious and adverse events have been reported following the use of each of them. International collaboration in the use, testing, and surveillance of vaccines would help limit these problems. National immunization programs must rely on comprehensive and timely surveillance and have the capability to react quickly to minimise negative outcomes. In each individual case, it may be difficult to demonstrate or rule out a relationship between a vaccine and an adverse event because there is usually no clear marker of etiology. Postmarketing surveillance of vaccines could be defined as the coordinated, structured, systematic, ongoing collection of data on the impact of licensed vaccines and their subsequent epidemiologic analysis and dissemination to manufacturers, regulators, health care providers, and the public. Managers of immunization programs have the responsibility for determining the risks associated with each vaccine, for constantly weighing the risks and benefits of vaccine use, and for minimizing the risks. Postmarketing surveillance of illness following administration of immunizing agents permits: 1) identification of illness or other side effects caused by immunizing agents; 2) estimation of the incidence of serious side effects of immunization; 3) monitoring for unusually high rates of adverse events (including lot-by-lot surveillance); 4) raising of health care providers' awareness to the risks and/or safety measures in administering vaccines; 5) identification of issues that require epidemiological research; and 6) identification of problems that require immediate epidemiological investigation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse events temporally associated with immunizing agents

In Canada during 1990, a total of 2832 reports of adverse events temporally associated with the administration of immunizing agents were received by the Childhood Immunization Division of the Laboratory Centre for Disease Control. This paper summarizes the data collected, describes the surveillance system, and demonstrates that, with more than 12,000,000 doses of vaccines distributed during 1990, the incidence of adverse events reported is very low.