Safety and Immunogenicity of a Pentavalent Combination Vaccine (Diphtheria, Tetanus, Acellular Pertussis, Polio and Haemophilus Influenzae Type b Conjugate) When Administered as a Fourth Dose at 15 to 18 Months of Age

A DTaP-IPV//PRP-T combination vaccine (Pentacel) has been universally used in Canada to provide immunization against diphtheria, tetanus, pertussis, polio, and Haemophilus influenzae type b with single injections at 2, 4, 6 and 18 months of age. This randomized, multicenter study was conducted to evaluate administration of a fourth dose of DTaP-IPV//PRP-T at 15 to 18 months of age, similar to the US immunization schedule. Participants who had received three doses of DTaP-IPV//PRP-T by 8 months of age were enrolled at 12 months and randomized to receive a fourth dose at 15, 16, 17 or 18 months. Antibody levels for each vaccine antigen were measured prior to and four weeks following booster vaccination. Overall, 1782 subjects were immunized and monitored for adverse events, and 735 were evaluated for immune responses. Preimmunization antibody levels differed minimally by age, for all antigens. The immune responses elicited by DTaP-IPV//PRP-T were comparable between participants vaccinated at 15 or 16 months and those vaccinated at 17 or 18 months, as demonstrated by specific antibody geometric mean titers, seroprotection/seroresponse rates, and reverse cumulative distribution curves. The fourth dose was well tolerated in all age groups. Toddlers at 15, 16, 17 or 18 months of age are equally suitable recipients for booster immunization with the DTaP-IPV//PRP-T vaccine.

An adolescent-adult formulation tetanus and diptheria toxoids adsorbed combined with acellular pertussis vaccine has comparable immunogenicity but less reactogenicity in children 4-6 years of age than a pediatric formulation acellular pertussis vaccine and diphtheria and tetanus toxoids adsorbed combined with inactivated poliomyelitis vaccine

In Canada, the fifth dose of the routine childhood immunization schedule against diphtheria, tetanus, pertussis and polio is given at 4-6 years of age. Up to 30% of children may have significant local reactions (redness, swelling) and this may be related to pertussis and diphtheria antigen content. We sought to determine if a combination product with lower content of pertussis and diphtheria toxoids (dTap) would result in fewer local reactions and not have inferior immunogenicity to a combination vaccine with higher pertussis and diphtheria content (diphtheria-tetanus-acellular pertussis-inactivated polio virus, DTaP-IPV). Healthy children aged 4-6 years with complete primary immunization series and a fourth dose of diphtheria and tetanus toxoids component pertussis inactivated polio and Haemophilus influenzae type B conjugate vaccine were randomized to one dose of dTap, followed in 4-6 weeks by one dose of IPV or control DTaP-IPV. Immediate reactions within 30 min, solicited injection site and systemic reactions within 14 days, and unsolicited adverse events (AE) within 6 weeks post-vaccination were monitored. Serum was collected prior to immunization, and 4-6 weeks after vaccine for diphtheria, tetanus and pertussis antibodies (Ab). Sample size was designed to detect > or =10% difference in injection site erythema, pain or swelling between groups 593 children at eight Canadian sites completed the study; no participant withdrew because of an AE. All safety endpoints on days 0-14 were less frequent in children randomized to the dTap than DTaP-IPV group: erythema (34.6% versus 51.7%), swelling (24.2% versus 33.8%) and pain (39.6% versus 67.2%). Fever was also less common (8.72% versus 16.9%). All children in both study groups had seroprotective Ab levels to diphtheria and tetanus at 4-6 weeks (> or =0.10 IU/mL). The majority of children in each vaccine arm had a four-fold increase in pertussis antibodies. Fever and injection site reactions are less common in 4-6 year-old-children who receive a dTap vaccine compared to DTaP-IPV, without inferior immunogenicity.

An adult formulation of a five-component acellular pertussis vaccine combined with diphtheria and tetanus toxoids is safe and immunogenic in adolescents and adults

Pertussis is increasingly being recognized as an important cause of cough illness in adolescents and adults. To evaluate the safety and immunogenicity of an adult formulation of a five-component (pertussis toxoid, filamentous hemagglutinin, pertactin, fimbriae 2 and 3) acellular pertussis vaccine combined with diphtheria and tetanus toxoids, we randomly allocated 749 healthy adolescents and adults from 12-54 years of age recruited from five Canadian communities to receive either tetanus-diphtheria vaccine (Td), acellular pertussis vaccine (aP) or combined diphtheria-tetanus-acellular pertussis vaccine (TdaP). Subjects and personnel were unaware of the vaccine allocation. Antibody levels were measured before and one month postimmunization; adverse events were collected at 24 and 72 h and 8 to 10 days. Adverse events were reported in similar frequency amongst the three vaccine groups. Moderate pain at the injection site was reported less frequently in the aP group than the TdaP group (10.7% compared to 19.4%; relative risk 0.6, 95% confidence interval 0.3-0.9). Chills were reported less frequently after Td (5.3%) than after TdaP (12.5%; relative risk 0.4, 95% confidence interval 0.2-0.9). There were no statistically significant differences between recipients of Td and TdaP in tetanus and diphtheria antitoxin levels achieved. Antibody response against Bordetella pertussis antigens was vigorous in all groups although recipients of aP alone had higher levels of antibody levels against pertussis toxoid, fimbriae, and agglutinins and lower antibody levels against pertactin than did TdaP recipients. We conclude that this adult formulation 5-component acellular pertussis vaccine is safe and immunogenic in adolescents and adults and is a candidate vaccine for adolescent and adult immunization programs.

Comparison of a fifth dose of a five-component acellular or a whole cell pertussis vaccine in children four to six years of age

BACKGROUND AND OBJECTIVES

Acellular pertussis vaccines are now preferred for all five childhood immunization doses; however, there are few data on the safety and immunogenicity of five consecutive doses. This study compared a fifth dose of an acellular and a whole cell pertussis vaccine in 4- to 6-year-old children previously immunized with four doses of acellular or whole cell pertussis vaccine.

STUDY DESIGN

In a double blind, multicenter study, 366 healthy children were randomly allocated to receive a single injection of a 5-component acellular or a whole cell pertussis vaccine, each combined with diphtheria and tetanus toxoids and inactivated poliovirus vaccine.

RESULTS

Although injection site redness > or =50 mm and swelling > or =50 mm were common in children who had received five doses of acellular (50% and 48.1%, respectively) or whole cell (66.2% and 59.7%) pertussis vaccine, limb soreness and limitation of motion were less frequently reported after acellular (1.9% and 0%) than after whole cell (49.2% and 36.3%; P < 0.0001) pertussis vaccine. Pre-fifth dose antipertussis antibody titers were higher in children who previously had received four doses of acellular pertussis vaccine. Postimmunization antibody titers against pertussis toxin, filamentous hemagglutinin, pertactin and tetanus toxin were higher in recipients of five doses of acellular pertussis vaccine, whereas antibody titers to diphtheria toxin, pertussis fimbriae and poliovirus serotypes were higher in recipients of five doses of the whole cell pertussis vaccine (P < 0.05 for all comparisons).

CONCLUSIONS

A regimen consisting of five doses of a five-component acellular pertussis combination vaccine is safe and immunogenic in pre-school children. Local adverse reactions are common but are less painful and activity-limiting than a regimen of five doses of a whole cell pertussis vaccine.

Extended follow-up of antibody levels and antigen responsiveness after 2 Haemophilus influenzae type b conjugate vaccines

Although immunization programs with Haemophilus influenzae type b (Hib) conjugate vaccines have dramatically reduced disease incidence, few data are available regarding the duration of protection after vaccination. We measured serum anti-polyribosylribitol phosphate (PRP) levels in healthy 4- to 5- year-old children previously given 4 doses of PRP-T vaccine (at 2, 4, 6, and 18 months) or 1 dose of PRP-D vaccine (at 19 months) during clinical trials to assess antibody persistence. Concurrent with other preschool immunizations, half of the children were randomly assigned to receive a PRP-T booster immunization to assess responsiveness. Among 136 subjects who were primed with PRP-D, the baseline geometric mean concentration of antibody was 0.7 microg/mL (95% CI 0.5 to 0.9). Concentrations were <0.15 microg/mL in 24 (17.6%) subjects. Among 212 children who were primed with PRP-T, the geometric mean concentration was 2.2 microg/mL (95% CI 1.9 to 2.5) (P <.001). Only 2 (0.9%) had concentrations <0.15 microg/mL. Four weeks after PRP-T immunization, geometric mean concentrations had increased to 98.4 and 102.0 microg/mL, respectively. Responses were strong even in those with low or undetectable preimmunization antibody levels. Spontaneous increases in antibody levels were seen in 9 (5.2%) of 172 subjects not given additional PRP-T. We concluded that among 4- to 5-year-olds, anti-PRP levels remained above 0.15 microg/mL in nearly all children after PRP-T priming and in most after PRP-D priming, and that both groups were able to respond vigorously to restimulation, consistent with persistent immune memory.

A comparative study of PENTA vaccine booster doses given at 12, 15, or 18 months of age

For infants immunized with Haemophilus influenzae type b conjugate vaccines, booster immunization is usually recommended in the second year of life, typically between 12 and 18 months. This study assessed the effect of age at booster immunization on pre-immunization antibody trough levels and on subsequent responses, for a PRP-T conjugate vaccine. Subjects were healthy children who had received PENTA vaccine (DPT-IPV/PRP-T combination) as infants. They were enrolled and given measles-mumps-rubella vaccine (MMR) at 12 months of age, then randomly assigned to receive PENTA vaccine concurrently with MMR or at 15 or 18 months of age. Parents were asked to note any adverse effects after PENTA vaccination. Blood samples were obtained prior to PENTA vaccination and 4 weeks later, and tested for antibodies to each antigen. In total 253 children received PENTA vaccine: 86 at 12 months, 85 at 15 months and 82 at 18 months. Injection site redness and swelling were least extensive in the youngest group (p < 0.001) but their rates of occurrence did not differ with age. Anti-PRP levels were similar in each age group prior to immunization; post-booster geometric mean concentrations (GMCs) ranged from 13.0 microg/ml in the youngest to 33.9 microg/ml in the oldest subjects (p < 0.0001). For each of the other antigens examined, booster responses were strongest at 18 months. We conclude that anti-PRP levels are stable between 12 and 18 months in children previously given PRP-T vaccine. PENTA boosters given at 12 months appear to cause milder injection site morbidity whereas those given at 18 months result in stronger responses to virtually every constituent antigen, although each age group responded satisfactorily.

Costs and cost-effectiveness of a universal, school-based hepatitis B vaccination program

OBJECTIVES

This study evaluated the costs and cost-effectiveness of a school-based grade 6 universal vaccination program against hepatitis B.

METHODS

We performed a descriptive cost study and cost-effectiveness analysis of British Columbia's vaccination program for 1994 and 1995. Since 1992, public health nurses have administered hepatitis B vaccine to grade 6 students in schools. We measured costs of vaccine, vaccine administration, and net program costs and used a validated Markov model to calculate the cost-effectiveness of the program.

RESULTS

Vaccinating each student cost $44, $24 of which was the cost of vaccine administration. The net cost was $9 per person; considering productivity costs, net savings were $75 per person. Marginal cost per life year gained was $2100. Universal adolescent vaccination is also economically attractive in the United States but less attractive in regions with incidence rates below 3 cases per 100,000 per year.

CONCLUSIONS

Hepatitis B vaccine can be delivered in North American schools at a reasonable cost. Adolescent vaccination is economically attractive in North American regions of high and average incidence rates. Our analysis supports vaccination in adolescents who remain at risk for hepatitis B virus infection.

Safety and immunogenicity of a combined five-component pertussis-diphtheria-tetanus-inactivated poliomyelitis-Haemophilus B conjugate vaccine administered to infants at two, four and six months of age

Safety, immunogenicity and lot consistency of five-component pertussis combination vaccine (CPDT-IPV//PRP-T) in infants were compared to that of whole cell pertussis combination vaccine (DPT-IPV//PRP-T), as were separate and combined injections of CPDT-IPV and PRP-T. No significant differences in adverse event rates were observed between lots of CPDT-IPV//PRP-T or between separate or combined injections of CPDT-IPV and PRP-T. Minor differences in antibody responses were observed between lots of component pertussis vaccine. Higher concentrations of diphtheria and tetanus antitoxins were induced by separate than by combined injection of CPDT-IPV and PRP-T, but no other differences in immunogenicity were observed. Adverse reactions were more than twice as frequent after whole cell than after component pertussis vaccines. Antibody responses to pertussis toxoid, filamentous hemagglutin and pertactin were significantly greater after component vaccines, while the response to type 3 poliovirus was higher after whole cell vaccine. No significant differences were observed for other vaccine components. CPDT-IPV//PRP-T was safe and immunogenic in infants. Antibody results were similar to those observed in a Swedish field trial that demonstrated CPDT to be 85% effective in preventing clinical pertussis.

Safety and immunogenicity of two inactivated poliovirus vaccines in combination with an acellular pertussis vaccine and diphtheria and tetanus toxoids in seventeen- to nineteen-month-old infants

OBJECTIVES

To compare the safety and immunity of an acellular pertussis vaccine containing pertussis toxoid, filamentous hemagglutinin, 69 kd protein, fimbriae 2 and 3 combined with diphtheria and tetanus toxoids given as single or separate injection with inactivated poliovirus vaccine (MRC-5-or Vero cell-derived) or live attenuated polio vaccine.

METHODS

A total of 425 healthy children between 17 and 19 months of age who were receiving the fourth dose of their routine immunization series were randomly allocated to receive either the acellular pertussis vaccine and oral poliovirus vaccine or one of two inactivated poliovirus vaccines as a combined injection or separate injections.

RESULTS

Although minor adverse events were commonly reported, differences between the groups were few. Fever and decreased feeding were less common in recipients of live attenuated poliovirus vaccine than the combination vaccine containing MRC-5 cell-derived inactivated poliovirus vaccine. A significant antibody response was demonstrated in all groups against all the antigens contained in the vaccines. Antibodies against poliovirus were higher in the groups immunized with the inactivated poliovirus vaccine than the live attenuated vaccine. Anti-69 kd protein antibodies were higher in the group given the MRC-5 cell-derived inactivated poliovirus vaccine as a combined injection than in the group given the separate injection or the group immunized with the live attenuated poliovirus vaccine.

CONCLUSION

The five-component acellular pertussis vaccine combined with diphtherid and tetanus toxoids is safe and immunogenic when combined with either MRC-5- or Vero cell-derived inactivated poliovirus vaccine. This will facilitate the implementation of acellular pertussis vaccine and the movement to inactivated poliovirus vaccine programs.

Safety and immunogenicity of an acellular pertussis diphtheria tetanus vaccine given as a single injection with Haemophilus influenzae b conjugate vaccine

To determine if an acellular pertussis-diphtheria-tetanus vaccine could be combined with a Haemophilus influenzae b conjugate vaccine as a single injection, we randomized 468 children between 17 and 21 months of age previously immunized with three doses of each vaccine to receive a five-component acellular pertussis vaccine combined with diphtheria and tetanus toxoids, and Haemophilus influenzae b-tetanus toxoid conjugate vaccine either as separate injections on separate days, separate injections on the same day, or as a single combined injection. Rates of adverse reactions were similar amongst the groups except for increased injection site tenderness (29.2% vs 17%, RR 1.76, 95% CI 1.09-2.85) and fussiness (36.4% vs 23.3%, RR 1.59, 95% CI 1.05-2.41) in the group given the combined injection rather than separate injections on separate days. Antibody levels against the capsular polysaccharide of H. influenzae b after the single combined injection (47.1 micrograms ml-1) were lower than after separate injections on the same day (66.0 micrograms ml-1; P < 0.05) but higher than when the injections were administered on separate days (28.4 micrograms ml-1; P < 0.001). We conclude that the five-component acellular pertussis vaccine is safe and immunogenic when combined with diphtheria and tetanus toxoids and H. influenzae b-tetanus toxoid conjugate vaccine in children receiving the fourth dose of the immunization series.

Adverse reactions and antibody response to four doses of acellular or whole cell pertussis vaccine combined with diphtheria and tetanus toxoids in the first 19 months of life

To assess the safety, immunogenicity, and lot consistency of a five-component acellular pertussis vaccine combined with diphtheria and tetanus toxoid (Connaught Laboratories Limited), we randomly allocated 432 infants to receive one of three lots of an acellular pertussis vaccine or a single lot of whole cell pertussis vaccine. Infants were immunized at 2, 4 and 6 months of age and between 17 and 19 months of age. Local and systemic adverse reactions were reported significantly more frequently by recipients of the whole cell than acellular vaccine after each dose. The antibody response against pertussis toxin, filamentous hemagglutinin, and 69 kDa protein was of greater magnitude in acellular pertussis vaccine recipients than whole cell pertussis vaccine recipients. Small differences were detected amongst the vaccine lots tested. We conclude that the acellular pertussis vaccine is safe and immunogenic for the first four doses in children under 2 years of age.

Safety and immunogenicity of two acellular pertussis vaccines with different pertussis toxoid and filamentous hemagglutinin content in infants 2-6 months old

The optimal composition and antigen content of acellular pertussis vaccines is not known. Two vaccines with different quantities of pertussis toxoid (10 and 20 micrograms) and filamentous hemagglutinin (5 and 20 micrograms) and identical 69 kD protein (3 micrograms) and fimbriae 2 and 3 (5 micrograms) combined with diphtheria and tetanus toxoids were compared in a randomized, double-blind study in 2,050 infants undergoing their primary immunization series at 8 centers in the US and Canada. A 6:1 increased antigen to lower antigen allocation was used; 96% of infants received 3 doses and completed the study. A 'clinically significant' local reaction was reported in 3-6% of participants after each dose. Erythema was the most common reaction occurring in 3-5% of infants after the second or third dose. A clinically significant systemic adverse reaction was reported in 28-34% of vaccinees (or vaccinated children) after each dose; fever (7-18%) and fussiness (12-17%) were most common. There were no differences in adverse events between the 2 vaccine formulations. Antibody responses were measured in 292 infants at 1 center. At 7 months, geometric mean anti-filamentous hemagglutinin antibody titers were higher in recipients of the higher antigen content vaccine (p < 0.001) whereas recipients of the lower antigen content formulation had higher anti-fimbriae antibody (p < 0.001) and agglutinin titers (p < 0.05). No differences were detected in anti-pertussis toxin or other antibody responses between the formulations. We conclude that increasing the antigen content of the acellular pertussis vaccine had a variable effect on antibody response but was not associated with increased adverse reactions.

Evaluation of booster doses of Haemophilus influenzae type b-tetanus toxoid conjugate vaccine in 18-month-old children

A booster dose of Haemophilus influenzae type b conjugate vaccine in the second year of life is the final step in the recommended series of doses to protect infants from invasive infection. This study assessed the safety and immunogenicity of PRP-T conjugate vaccine booster doses (Act-HIB, Connaught Laboratories Ltd). The participants were 367 healthy children who had taken part in a study of primary immunization with PRP-T. At 18-19 months old, subjects were randomly assigned to receive diphtheria-pertussis-tetanus (DPT) and PRP-T vaccines either mixed in one syringe (n = 183) or separately in opposite limbs (n = 184). Adverse events were monitored for 48 h after immunization. Blood was obtained prior to vaccination in half of the subjects (combined injections group) and following vaccination in all subjects to test for antibodies to each of the antigens administered. Local adverse reactions were infrequent with PRP-T alone and equally frequent at sites of DPT or DPT/PRP-T injection, except for redness > or = 25 mm in diameter which was more frequent after the combined vaccines (25.1 versus 14.1%, p < 0.01). Systemic adverse events did not differ in type or frequency between groups. Before immunization, the geometric mean anti-PRP level in those tested was 0.41 micrograms ml-1; 26.7% had levels below 0.15 micrograms ml-1. Both treatment groups responded strongly to vaccination. In those serially tested, anti-PRP levels rose by over 90-fold, to 38.1 micrograms ml-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and immunogenicity of Haemophilus influenzae vaccine (tetanus toxoid conjugate) administered concurrently or combined with diphtheria and tetanus toxoids, pertussis vaccine and inactivated poliomyelitis vaccine to healthy infants at two, four and six months of age

The safety and immunogenicity of Haemophilus influenzae vaccine (tetanus toxoid conjugate (PRP-T) administered concurrently in separate sites or mixed in the same syringe with diphtheria and tetanus toxoids, pertussis vaccine and inactivated poliomyelitis vaccine were assessed in 439 infants at 2, 4 and 6 months of age. The proportions with local redness, tenderness and swelling in the separate and combined groups were 18% vs. 11% (P < 0.001), 27% vs. 24% and 15% vs. 13%, respectively. Systemic reactions occurred at similar rates in both groups. The combined vaccine induced tetanus and diphtheria antitoxin titers > or = 0.01 IU/ml in 99.5 and 99.1% of infants, pertussis agglutinin titers > or = 64 in 92.4%, anti-polyribosylribitol phosphate titers > or = 0.15 microgram/ml in 93.8% and > or = 1.0 microgram/ml in 75% and polio-neutralizing titers > or = 8 in > 98% of infants. However, antibody concentrations to PRP-T, some pertussis antigens and tetanus toxoid were significantly lower after combined than after separate injections of DPT/diphtheria and tetanus toxoids, pertussis vaccine and inactivated poliomyelitis vaccine and PRP-T. The clinical significance of these differences is not known, but the interactions observed among the components of the pentavalent vaccine may be of concern because they might influence antibody persistence until the fourth dose is administered.

Can Haemophilus influenzae type b-tetanus toxoid conjugate vaccine be combined with diphtheria toxoid-pertussis vaccine-tetanus toxoid?

OBJECTIVE

To assess the side effects and immune responses after three serial doses of PRP-T vaccine (a Haemophilus influenzae type b [Hib]-tetanus toxoid conjugate vaccine) given concurrently or mixed with adsorbed DPT vaccine (diphtheria toxoid-pertussis vaccine-tetanus toxoid).

DESIGN

Multicentre randomized controlled trial.

SETTING

Four public health units in western Canada.

PARTICIPANTS

Healthy infants 8 to 15 weeks old at entry who were able to receive routine primary vaccinations. Of 444 infants enrolled, 433 (98%) completed the study.

INTERVENTIONS

All infants received PRP-T and DPT vaccines at 2, 4 and 6 months of age: half received them mixed in one injection and the others as separate, bilateral injections.

MAIN OUTCOME MEASURES

Side-effects 24 and 48 hours after each dose and serologic responses to each vaccine component.

RESULTS

Follow-up was obtained after all 1312 vaccinations. Fever was infrequent in the two treatment groups. Local adverse effects of the PRP-T vaccine were infrequent and mild (e.g., redness was noted in 5.9% of cases and the area of redness was more than 2.5 cm in diameter in 0.8%). The incidence rate of local effects of the DPT-containing vaccines was the same in the two groups except for tenderness, which was more frequent in the group given the mixed vaccine (26.6% v. 17.9%, p < 0.001). Serologic data were available for 97% of the subjects. After the three doses 98.1% of the subjects had a PRP antibody level of 0.15 micrograms/mL or more, and 87.9% had a level of 1.0 micrograms/mL or more, both levels compatible with protection against Hib. Responses to PRP-T were comparable between the treatment groups as were responses to the diphtheria and tetanus toxoids. Pertussis agglutinin titres were reduced after administration of one of two PRP-T lots mixed with DPT vaccine, but responses to four other pertussis antigens were not impaired.

CONCLUSION

PRP-T vaccine is well tolerated and immunogenic. Combined PRP-T and DPT vaccines performed satisfactorily and may be the preferred method of administration.

A swimming pool-associated outbreak of Cryptosporidiosis in British Columbia

An outbreak of Cryptosporidiosis occurred over three months in a British Columbia community, peaking in December 1990. Results of the case-control study and illness surveys support the hypothesis that transmission occurred in a public children's pool at the local recreation centre. Analysis using lab-confirmed cases revealed a matched odds ratio of 4.5 [95% CI 0.97, 20.83], and using clinical cases an unmatched odds ratio of 12.8 [95% CI 3.68, 46.77], associated with swimming in the children's pool within two weeks prior to onset of illness. Other risk factors were not significant. Attack rates in various groups of children's pool users ranged from 8% to 78%. The children's pool was closed for steam cleaning and disinfection. Unusually frequent defecations including liquid stools had occurred before and during the outbreak. Improvements were instituted for removal of feces and superchlorination of pool water.

Controlled trial of Haemophilus influenzae type B diphtheria toxoid conjugate combined with diphtheria, tetanus and pertussis vaccines, in 18-month-old children, including comparison of arm versus thigh injection

A randomized, controlled comparison was made in 175 healthy 18-month-old children given either diphtheria and tetanus toxoids and pertussis vaccine, adsorbed (DTP) and haemophilus b diphtheria toxoid conjugate vaccine (PRP/D) concurrently at separate sites (66 children) or a new vaccine combining these products (109 children). Rates of local or systemic adverse effects postimmunization and antibody responses to each component did not differ significantly between groups. DTP-containing vaccines were better tolerated when given in the thigh than in the arm. The combination DTP-PRP/D vaccine performed satisfactorily at 18 months of age, avoiding the inconvenience of two injections.

Giardiasis outbreak from a chlorinated community water supply

A giardiasis outbreak from a chlorinated, unfiltered surface water supply in Penticton, British Columbia (pop. 25,000) from June to August 1986 resulted in 362 laboratory-confirmed cases. A telephone survey estimated an attack rate of over 12%. A reservoir pond containing Giardia-infected beaver was implicated as the source. A case-control study with 65 cases did not find any significant associations. A retrospective case-finding survey of records from eight (out of 35) general physicians estimated that 1,500 physician visits occurred and produced an epidemic curve in close parallel with that from laboratory-confirmed and reported cases. Despite improvements on the reservoir, another outbreak occurred when this water source was reinstituted in October for several weeks, confirming our conclusion that it was the source of the first outbreak. Various options for reducing the risk of future outbreaks are being explored including full water treatment.