Partial uptake of varicella vaccine and the epidemiological effect on varicella disease in 11 day-care centers in North Carolina

BACKGROUND

The increasing use of varicella vaccine in children attending day care has rapidly decreased the incidence of wild-type varicella disease. The herd immunity noted is significant and will have an effect on the epidemiology of natural varicella.

OBJECTIVE

To monitor the change in varicella incidence in day-care attendees after the licensure of varicella vaccine.

DESIGN

A prospective observational cohort study design.

SETTING

Eleven private day-care centers and preschools in North Carolina participated in the study from January 1, 1995, through December 31, 1999.

PARTICIPANTS

All children in the 11 centers were eligible for participation. Some participated more actively, supplying information on a regular basis. Others participated passively. Day-care personnel provided information about all cases of varicella.

INTERVENTIONS

None.

MAIN OUTCOME VARIABLES

The change in the incidence of varicella disease was documented as the use of varicella vaccine increased.

RESULTS

Varicella vaccine coverage increased substantially from 4.4% in 1995 to 63.1% in December 1999. The vaccination rate accelerated dramatically in 1996 and 1997, leveled off in 1998, and rose again in 1999. Cumulative varicella incidence decreased from 16.74 cases per 1000 person-months in July 1996 to 1.53 cases per 1000 person-months in December 1999 in unvaccinated children.

CONCLUSIONS

The varicella vaccination rate continued to increase slowly in the day-care population after an initial rapid uptake. The decrease in varicella disease is greater than the increase in varicella vaccination. This herd effect is welcome and even apparent in the unvaccinated children younger than 1 year.

Postlicensure study of varicella vaccine effectiveness in a day-care setting

BACKGROUND

Varicella vaccine has been licensed for use in the United States since the spring of 1995. The acceptance of the vaccine and its effect on varicella incidence in children is important.

AIM

To document the effectiveness of the varicella vaccine in children attending day care in 11 centers in North Carolina.

METHODS

A dynamic cohort study design was used in 11 day-care centers in North Carolina. Multiple cross-sectional evaluations were performed and children were noted to be vaccinated or not and diseased or not. Vaccine effectiveness was estimated by comparing the varicella attack rate in the vaccinated with the varicella attack rate in the unvaccinated. Person time was used as the denominator for all calculations.

RESULTS

During the study period February 1, 1996, to September 1, 1997, 134 cases of varicella occurred in the unvaccinated and 11 cases occurred in the vaccinated children. The attack rates in the vaccinated and unvaccinated were 2.49 and 14.66, respectively, for an overall vaccine effectiveness of 83% for mild/moderate disease.

CONCLUSIONS

In the day-care setting varicella vaccine demonstrated benefit in preventing and modifying wild-type varicella disease.

Concurrent administration of inactivated hepatitis A vaccine with immune globulin in healthy adults

301 healthy adult volunteers were randomized to one of three treatment groups: inactivated hepatitis A vaccine alone; inactivated hepatitis A vaccine with immune globulin (Ig) concurrently; or Ig alone. The first two treatment groups received a second dose of hepatitis A vaccine at week 24. Anti-HAV was measured 4, 8, 12, 24 and 28 weeks after the primary immunization. When comparing subjects receiving inactivated hepatitis A vaccine alone to those receiving vaccine and Ig, the seropositivity rates were not significantly different at 4, 8, 12 and 28 weeks, but at week 24 the seropositivity rate was lower in the group receiving both vaccine and Ig compared to the group receiving vaccine alone (92.0% compared to 97.0%). At weeks 8, 12 and 24 the geometric mean titers (GMTs) were significantly lower for subjects receiving both vaccine and Ig. The GMTs were not significantly different after the second dose of vaccine. At all time points, the lower serum antibody concentrations observed in subjects receiving both inactivated hepatitis A vaccine and Ig were nevertheless substantially higher than the cutoff for assay seropositivity and much higher than after Ig alone; these differences are therefore clinically insignificant.

Modified varicella-like syndrome

After incidental exposure to natural varicella, up to 18% of vaccinees reported a breakthrough infection known as modified varicella-like syndrome (MVLS) over up to 10 years of postvaccination follow-up, compared with natural varicella occurring in similarly aged unvaccinated children at the rate of 9% per year. Children with MVLS are frequently asymptomatic, and their disease is characterized by having fewer lesions, less fever, and lasting fewer days than natural varicella. When a case of MVLS occurs there are few secondary cases, suggesting that it is infrequently transmitted. Sequelae such as secondary bacterial infection, cerebellar ataxia, encephalitis, and pneumonia occur infrequently.

A case-control study examining risk factors for invasive Haemophilus influenzae type b disease in Victoria, Australia 1988-90

OBJECTIVE

To determine whether day-care attendance was a risk factor for Haemophilus influenzae type b (Hib) disease, particularly for epiglottitis.

METHODOLOGY

A case-control analysis of risk factors for invasive Hib disease was performed in Victoria, Australia between February 1988 and February 1990 prior to the introduction of immunization for Hib. A total of 210 cases and 367 day surgery hospital controls were enrolled prospectively. Data were collected by questionnaire at the time of admission.

RESULTS

Logistic regression analysis showed that risk factors for meningitis were day-care attendance, household crowding and recent illness in a sibling. Risk factors for epiglottitis were day-care attendance and mother's birthplace in Australia or New Zealand.

CONCLUSIONS

This study confirms that day-care attendance is a risk factor for Hib epiglottitis as well as meningitis. In addition, the mother's birthplace in Australia or New Zealand is a risk factor for epiglottitis in these data. The reason for this latter observation is unclear.

Influenza A vaccine decreases the incidence of otitis media in 6- to 30-month-old children in day care

OBJECTIVE

To determine if the use of influenza vaccine in children in day care decreases the incidence of otitis media during the influenza season.

DESIGN

Prospective cohort study.

SETTING

Eight day-care centers in North Carolina.

PARTICIPANTS

One hundred eighty-six children aged 6 to 30 months.

INTERVENTION

Half the participants received trivalent subvirion influenza virus vaccine.

MEASUREMENTS

Acute otitis media (AOM) and serous otitis media (SOM) were assessed biweekly from mid-November 1993 to mid-March 1994 by visual and tympanometric examinations performed by "blinded" observers. The winter season was divided into three periods-before, during, and after influenza season--and the number of children with AOM or SOM during each period was determined. Unadjusted and adjusted odds ratios (ORs) were computed, while controlling for race and sex using logistic regression methods.

RESULTS

Influenza vaccine was protective against AOM (OR = 0.69, 95% CI, 0.49-0.98) during the influenza season. Although there may have been some protection against SOM (OR = 0.75, 95% CI, 0.54-1.02) statistical significance was not achieved. Myringotomy tubes were also significantly protective against AOM and SOM during all three time periods, with ORs between 0.34 and 0.52, but the greatest protection was seen during the influenza period.

CONCLUSIONS

Influenza vaccination of 6- to 30-month-old children in day care was associated with a decreased incidence of otitis media during the influenza season. Myringotomy tubes protected against AOM and SOM during all 16 weeks monitored.

Over five-year follow-up of Oka/Merck varicella vaccine recipients in 465 infants and adolescents

A total of 465 healthy infants and adolescents ages 12 months to 17 years without a known history of varicella or recent exposure to varicella-zoster virus VZV were immunized with live attenuated Oka/Merck varicella vaccine from November, 1984, through April, 1989. The vaccine administered was from 1 of 7 production lots containing from 950 to 3265 plaque-forming units and was well-tolerated with few side effects. The seroconversion rate for seronegative subjects was 94.6% (403 of 426). This varied by lot from 85% (950 plaque-forming units) to 100% (3010 and 3265 plaque-forming units). Breakthrough disease after exposure to varicella in seroconverters during 5 to 10 years of follow-up was 18.6% (75 of 403). The breakthrough disease was characterized by a maculopapular rash with a median of 35 lesions, most of which were macules. Breakthrough disease lasted a median of 5 days and the median temperature was 99 degrees F; 65.3% (49 of 75) of subjects were afebrile and 2.7% (2 of 75) of subjects had temperatures of > 102.9 degrees F. Varicella vaccine provides excellent (94.6%) seroconversion, and most children who developed breakthrough disease (18.6%) experienced a modified, milder form of illness than has been observed with natural varicella in unvaccinated subjects.

Maternal acceptance of voluntary human immunodeficiency virus antibody testing during the newborn period with the Guthrie card

In order to provide the opportunity for women delivering newborns to have human immunodeficiency virus (HIV) testing we piloted a hospital-based voluntary HIV testing program during the newborn period using the Guthrie card. During the study period 789 women were offered newborn HIV antibody testing. Test acceptance during the newborn period (61.0%) was comparable to that reported for the prenatal period (60.6%). Overall 77.4% of women were tested in the newborn period or reported being tested in the prenatal period. Prenatal test acceptance best predicted newborn HIV test acceptance (odds ratio, 3.37; 95% confidence interval, 2.40 to 4.74). When compared to HIV testing during the newborn period prenatal HIV testing is preferable because it enables the recognition of HIV infection early during pregnancy and allows the mother the option to elect zidovudine therapy and potentially prevent infection in her newborn. However, when prenatal HIV testing is not routinely made available or cannot be assured, women should be offered the opportunity to be tested during the newborn period.

Clinical manifestations and outcome of Haemophilus influenzae type b disease

OBJECTIVE

To document clinical manifestations, laboratory findings and outcome of childhood Haemophilus influenzae type b (Hib) infections.

METHODOLOGY

Medical records of 235 children with Hib disease admitted to hospital during a 2 year period were reviewed; additional information was obtained by questionnaire and follow up 6 weeks after discharge.

RESULTS

Three-quarters of patients presented with either meningitis or epiglottitis. Children with epiglottitis were older, had shorter illnesses and were less likely to have had antibiotics before admission than those with meningitis; 38% of the latter had been given some antibiotic therapy, with no apparent effect on the outcome. Fever persisted for 7 days or more in 23% of patients with meningitis. Death from meningitis occurred in 3.8% of patients and was due to fulminating disease.

CONCLUSIONS

These data will assist in recognition and appropriate management of Hib disease as the clinical manifestations become less familiar following the introduction of immunization. Specific laboratory diagnosis is required for accurate surveillance, which should be maintained in order to ensure high immunization rates.

Cost of treatment and prevention of Haemophilus influenzae type b disease. An international perspective

On the basis of immunogenicity and protective efficacy studies, 4 Haemophilus influenzae type b (Hib) conjugate vaccines have been licensed for administration to infants and children. Population based studies of Hib disease from Australia, Chile, Finland, Gambia, Israel, Switzerland, UK and US show that the relative and absolute incidence of Hib disease varies significantly. These differences in Hib epidemiology, and associated sequelae and hospital costs affect the cost-benefit analysis of preventive vaccination, necessitating unique calculations for each country. Published papers on the cost of Hib disease and the cost-benefit relationship of Hib vaccination have been based primarily on reports from the US, but more recently also on studies from Australia, Finland, Israel, Switzerland, UK, Sweden and Chile. All studies to date have produced favourable cost-benefit ratios. The implementation of Hib vaccination has led to the virtual disappearance of Hib disease in some of these countries. The lessons gained from these analyses are instructive not only for better understanding of the epidemiology of Hib disease, but also as a template for assessing the cost-benefit ratio of the implementation of preventive vaccination for other diseases.

Comparison of the epidemiology and cost of Haemophilus influenzae type b disease in five western countries

To determine and compare the cost of Haemophilus influenzae type b (Hib) disease in Australia, Finland, Israel, Switzerland and the United Kingdom a collaborative study was undertaken. The incidence of Hib disease varies in these 5 countries from 34 to 58.5 cases per 100,000 children less than 5 years of age. Although the incidence of meningitis in this age group is similar (between 18 and 26/100,000) in these countries, the incidence of epiglottitis varies from 0 to 22.7/100,000. The cost of hospitalization and the frequency of sequelae are similar for 4 of the 5 countries; however, the break even cost of a vaccination program to prevent 90% of Hib disease is estimated to vary from $22 to $84 per child (US$). Because of a lower incidence of Hib disease and lower cost for hospitalization, these costs are considerably less than those for the United States ($301.64 using similar calculations).

Activation of fibroblast growth factor (FGF) receptors by recombinant human FGF-5

We have purified biologically active recombinant human fibroblast growth factor 5 (FGF-5) from Escherichia coli. In the presence of heparin, recombinant FGF-5 is as active as native growth factor, demonstrating that glycosylation does not significantly potentiate FGF-5 activity. FGF-5 can bind and induce autophosphorylation of human FGF receptors (FGFR) 1 and 2. Competition binding studies show that the KD for FGF-5-FGFR-1 and FGF-5-FGFR-2 interactions are both between 0.5 and 1.5 x 10(-9) M.

Outer membrane protein subtypes of Haemophilus influenzae type b isolates causing invasive disease in Victoria, Australia, from 1988 to 1990

Outer membrane protein subtyping of 187 isolates of Haemophilus influenzae type b (Hib), isolated from children with invasive Hib disease in Victoria, Australia, showed that a single outer membrane protein subtype (1VA) was responsible for 83% of the infections. It was identical to that responsible for the majority of cases of invasive Hib disease in Europe.

Socioeconomic risk factors for invasive Haemophilus influenzae type b disease

Socioeconomic risk factors for primary invasive Haemophilus influenzae type b (Hib) disease include factors that increase exposure to Hib (day care attendance, presence of siblings, and crowded households) and factors that increase an individual's susceptibility to Hib infections (short duration of breast feeding, parental smoking, and frequent infections in general). These factors are consistently found to be associated with risk of Hib disease in studies conducted in populations that differ in their Hib disease epidemiology. However, there are large differences in the prevalence of these risk factors among populations. According to present knowledge, variations in the prevalence of socioeconomic risk factors may explain most of the differences in the epidemiology of Hib disease and may also contribute to the differences in Hib vaccine efficacy in different populations.

Pertussis immunization in eight-month-old children in North Carolina

Between 1984 and 1987 reported pertussis cases in North Carolina increased threefold. Pertussis immunization rates were examined for those years in three one-year cohorts drawn from a random selection of North Carolina birth records. The percentage of children immunized with three DTPs at eight months of age was 58.1, 58.6, and 56.7 for the three cohorts. Only 20.5 percent of 117 reported pertussis cases in children 9-36 months of age during the last 10 years were adequately immunized. The low pertussis immunization rate may have contributed to the recent increase in pertussis cases in North Carolina.

Haemophilus influenzae type b infections in Victoria, Australia, 1985 to 1987

Invasive Haemophilus influenzae type b (HIB) infections occurring from 1985 to 1987 in children younger than 16 years of age living in the state of Victoria were reviewed. There were 547 cases which fulfilled the case definition, including 231 cases of meningitis, 219 of epiglottitis and 97 other infections; 14 (2.6%) children died, 8 with meningitis, 5 with epiglottitis and 1 with pneumonia. Ninety-five percent of cases occurred in children younger than 5 years of age, in whom the case attack rate was 58.5/100,000/annum. Nearly two-thirds of cases (46% of meningitis; 91% of epiglottitis; 45% of other infections) occurred in children more than 18 months of age (the age at which vaccine is presently given in the United States). Compared with the United States, the case attack rate for HIB disease in Victoria is lower, the mean age of affected children higher and the proportion with epiglottitis is greater. However, the incidence, age distribution and clinical manifestations of HIB disease in Victoria are similar to those described in Scandinavia before the successful introduction of vaccines. Effective conjugate vaccines against HIB disease are now available and the majority of cases are preventable (depending on the immunization schedule used). These data suggest that immunization of Victorian children against HIB infection should be cost-effective.

Antibody response of 18 month old children 1 month and 18 months following Haemophilus influenzae type b vaccine administered singly or with DTP vaccine

Seventy-six children (aged 17-19 months) received 10 micrograms of Haemophilus influenzae type b polyribosyl-ribitol phosphate (PRP) vaccine, diluted with either phosphate-buffered saline (PBS) or diphtheria-tetanus-pertussis (DTP) vaccine, in a single-blind randomized trial. There were few side effects when PRP was administered alone. Before vaccination 37 of 76 children (49%) had non-protective antibody levels (less than 0.15 micrograms/mL); 26 of these 37 (70%) achieved antibody levels of greater than 0.15 micrograms/mL 1 month after vaccination. Before vaccination 16 of 76 (21%) had antibody levels of greater than 1.0 micrograms/mL; 1 month after vaccination 39 of 76 children (51%) achieved levels of greater than 1.0 micrograms/mL. Of 12 infants who had antibody levels less than 0.15 micrograms/mL 1 month after immunization, 10 had protective levels 18 months later. Administration of PRP mixed with DTP did not affect antibody response to PRP. The potential use and limitations of PRP vaccine are discussed.