Human papillomavirus (HPV) types among Alaska native women attending a colposcopy clinic in Anchorage, Alaska, 2009-2011.

BACKGROUND: The first HPV vaccines licensed targeted two HPV types responsible for most cervical cancers. A 9-valent vaccine (9vHPV), targeting 5 additional types, was introduced in 2016 and is currently the only HPV vaccine available in the United States. Previous studies demonstrated high rates of HPV infection in Alaska Native (AN) women. We sought to measure prevalence of high risk HPV types in AN women undergoing colposcopy and to determine those preventable by vaccination. METHODS: For this cross-sectional study, we recruited women who were undergoing colposcopy for clinical indications at Alaska Native Medical Center to obtain cervical brush biopsy samples. Specimens were shipped to Atlanta, Georgia for DNA extraction, HPV detection, and typing using L1 PCR with type-specific hybridization to detect 37 HPV types. RESULTS: Four hundred eighty eight specimens from 489 women were tested. At least one HPV type was found in 458 (94%) specimens. Of 458 participants who were HPV positive, 332 (72%) had two or more types. At least one type targeted by 9vHPV was detected in 95% of participants with CIN 3 (21/22), 82% with CIN 2 (37/45), and 65% with CIN 1 (119/184). (p < 0.001) HPV 16 or 18 were detected in 77% (17/22) with CIN 3, 53% (24/45) with CIN 2, and 36% (67/184) with CIN 1. (p < 0.001). CONCLUSIONS: A substantial proportion of AN women attending colposcopy clinic had evidence of HPV 16/18 infection, as well as other high risk types targeted by 9vHPV. At least one 9vHPV type was detected in 62% of the participants overall, and 95% of participants with CIN3. AN women are expected to benefit from vaccination against HPV 16/18, and will have greater benefit from 9vHPV. Information from this study could be used to develop public health strategies to increase vaccine uptake, or to track HPV genotype prevalence over time.

Persistence of antibody to Hepatitis A virus 20 years after receipt of Hepatitis A vaccine in Alaska.

Hepatitis A vaccine is recommended for children ≥1 year old to prevent hepatitis A virus (HAV) infection. However, the duration of vaccine-induced immunity is unknown. We evaluated a cohort of Alaska Native persons 20 years after HAV vaccination. Children aged 3-6 years had been previously randomized to receive three doses of HAV vaccine (360 ELISA units/dose) at: (i) 0,1,2 months; (ii) 0,1,6 months; and (iii) 0,1,12 months. We measured anti-HAV antibody concentrations every 2-3 years; described geometric mean concentrations (GMC) and the proportion with protective antibody (≥20 mIU mL-1 ) over time; and modelled the change in GMC using fractional polynomial regression. Of the 144 participants, after 20 years 52 (36.1%) were available for the follow-up (17, 18, 17 children in Groups A, B and C, respectively). Overall, 46 (88.5%) of 52 available participants had anti-HAV antibody concentrations ≥20 mIU mL-1 , and overall GMC was 107 mIU mL-1 . Although GMC levels were lower in Group A (60; CI 34-104) than in Group B (110; CI 68-177) or Group C (184; CI 98-345) (B vs C: P=.168; A vs B/C: P=.011), there was no difference between groups after adjusting for peak antibody levels post-vaccination (P=.579). Models predicted geometric mean concentrations of 124 mIU mL-1 after 25 years, and 106 mIU mL-1 after 30 years. HAV vaccine provides protective antibody levels 20 years after childhood vaccination. Lower antibody levels in Group A may be explained by a lower initial peak response. Our results suggest a booster vaccine dose is unnecessary for at least 25-30 years.

Nested case-control study: hepatocellular carcinoma risk after hepatitis B surface antigen seroclearance.

BACKGROUND: Hepatocellular carcinoma (HCC) risk after resolving chronic hepatitis B virus (HBV) infection is unclear. AIM: To compare HCC risk between Alaska Native (AN) patients with and without hepatitis B surface antigen (HBsAg) seroclearance. METHODS: We selected persons with (case-patients) and without (control-patients) HBsAg seroclearance from a cohort of 1346 chronically HBV-infected AN patients followed during 1982-2013. We attempted to match two control-patients/case-patient on sex, HBV genotype, and age. Person-years of follow-up for case-patients began on the date of HBsAg resolution and for control-patients began on the date equivalent to the cohort entry date plus the years of HBsAg duration for their corresponding case-patient. We compared HCC risk using a Cox proportional hazards model. RESULTS: The 238 case-patients (4 with HCC) and 435 control-patients (9 with HCC) were similar in age [P-value (P) = 0.30], sex (P = 0.53) and HBV genotype (P = 0.99). Case-patients had longer person-years of follow-up than control-patients (11.7 vs. 10.1 years; P = 0.04). The HCC rate/100 000 persons was similar between case- (132) and control-patients (178; P = 0.65). The adjusted hazard ratio comparing case- and control-patients was similar for HCC [0.7; 95% confidence interval (CI): 0.2-2.4], increased for each 1-year increment for age (1.1; CI: 1.0-1.1; P < 0.01), and was greater if the initial HBeAg was positive (3.5; CI: 1.1-11.0; P = 0.03). CONCLUSIONS: Hepatitis B surface antigen seroclearance was not associated with reduced HCC risk; the HCC risk estimates are limited by wide 95% confidence intervals. Persons meeting HCC surveillance indications prior to HBsAg seroclearance could benefit from continued surveillance after seroclearance.

Evaluation of the response to a booster dose of hepatitis B vaccine in previously immunized healthcare workers.

INTRODUCTION: Hepatitis B vaccination is recommended for all healthcare workers (HCW) at risk of exposure to infectious body fluids. However, the absolute duration of protection from immunization is unknown. The purpose of this randomized comparison trial was to determine how previously immunized HCW respond to different booster doses of hepatitis B vaccine. METHOD: Adult HCW (n=59) were classified by level of hepatitis B surface antigen (anti-HBs), either <10 milli-International Units per milliliter (mIU/ml) or 10-50 mIU/ml. Participants were then randomized to receive a 2.5 or 10 microg dose of hepatitis B vaccine. Evaluation of anti-HBs levels were conducted 10 to 14 days, one month and one year postbooster. RESULTS AND DISCUSSION: All participants responded to the booster dose with increased anti-HBs levels. At 14 days, mean anti-HBs levels were significantly higher for those with higher levels at baseline (P=0.004) and those receiving the 10 microg dose (P=0.016). At one month, those with higher anti-HBs levels at baseline and those receiving the 10 microg dose were significantly higher (P<0.01 for both). At one year, the increase for the higher dose was no longer statistically significant when examined by itself (P=0.081); statistical significance (P=0.021) was achieved after adjusting for anti-HBs level at baseline. For all participants, the geometric mean anti-HBs level was 2618 mIU/ml at 14 days, 2175 mIU/ml at one month and 88.9 mIU/ml at one year. At all time points the increase in anti-HBs levels represented an increase over the geometric mean baseline level of anti-HBs (7.4 mIU/ml). Hepatitis B immunized adults responded to a booster dose of hepatitis B vaccine from 3 to 13 yr postvaccination series. Data support current recommendations that immunized HCW do not require periodic antibody testing or vaccine boosters.

Experience with the prevention of invasive Haemophilus influenzae type b disease by vaccination in Alaska: the impact of persistent oropharyngeal carriage.

OBJECTIVES: To report the epidemiology of invasive Haemophilus influenzae type b (Hib) disease in high-risk Alaska Native infants before and after universal infant Hib vaccination and evaluate an increase in invasive Hib disease in 1996 after changing Hib vaccine type. STUDY DESIGN: Statewide laboratory surveillance for invasive Hib disease has been conducted since 1980. Three cross-sectional Hib carriage studies were conducted in 1997 and 1998. RESULTS: The invasive Hib disease rate in Alaska Natives decreased from 332 cases per 100,000 children <5 years old in 1980-1991 to 17:100,000 in 1992-1995 but increased primarily in rural areas to 57.9:100,000 after a switch in Hib vaccine types. Carriage studies in 5 rural Alaska Native villages showed oropharyngeal Hib carriage as high as 9.3% in children aged 1 to 5 years; in contrast, carriage in urban Alaska Native children was <1%. CONCLUSIONS: Although Hib disease has decreased in Alaska, the rate of Hib disease and carriage in rural Alaska Natives did not decrease to the same extent as in non-Natives and urban Alaska Natives. Use of polyribosylribitol phosphate-outer-membrane protein conjugate vaccine for the first vaccine dose is critical to disease control in this population with continued transmission in infants <6 months of age. The ability to eliminate Hib carriage and disease may be affected by population characteristics, vaccination coverage, and Hib vaccine type used. This may pose a challenge to global elimination of Hib.

Serotype distribution and antimicrobial resistance patterns of invasive isolates of Streptococcus pneumoniae: Alaska, 1991-1998.

From January 1991 through December 1998, a total of 1046 pneumococcal isolates were received from 23 laboratories participating in the statewide surveillance system. Of these, 1037 were recovered from normally sterile sites (blood and cerebrospinal and pleural fluid) and were available for serotyping and susceptibility testing. Ninety-two percent of these isolates were serotypes represented in the 23-valent pneumococcal polysaccharide vaccine. Serotypes in the 7-valent pneumococcal conjugate vaccine (4, 6B, 9V, 14, 18C, 19F, and 23F) were recovered from 72% of Alaska Natives and 84% of non-Native children <5 years old with invasive disease. Statewide, 7.3% and 3.2% of isolates had intermediate and high levels of resistance to penicillin, respectively; 9.2% were resistant to erythromycin (minimal inhibitory concentration, >/=1 microg/mL) and 19% to trimethoprim/sulfamethoxazole (minimal inhibitory concentration, >/=4/76 microg/mL). Twelve percent of invasive isolates were resistant to >/=2 classes of antibiotics; of these, serotype 6B accounted for 33%, and 63% were recovered from children <5 years old.

Immunogenicity of a heptavalent pneumococcal conjugate vaccine in Apache and Navajo Indian, Alaska native, and non-native American children aged <2 years.

High rates of invasive pneumococcal disease have been described among infants living in various Native American communities. In this study, we evaluated the immunogenicity of a 7-valent pneumococcal vaccine consisting of serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F covalently linked to the outer membrane protein complex of Neisseria meningitidis in Apache and Navajo Indian, Alaska Native, and non-Native American children. The vaccine was administered at ages 2, 4, and 6 months; a booster dose was given at age 15 months. Levels of serotype-specific immunoglobulin G (IgG) were measured by a standardized enzyme-linked immunosorbent assay. The responses after 3 primary doses of vaccine were similar in all 3 groups of children, except for those to serotypes 14 and 23F. One month after the booster dose, geometric mean concentrations (GMCs) of serotype-specific IgG antibodies increased significantly in all 3 groups of children, compared with GMCs of IgG antibodies to pneumococcal serotypes before the booster dose.

Invasive Haemophilus influenzae disease in Alaskan residents aged 10 years and older before and after infant vaccination programs.

CONTEXT: The introduction of Haemophilus influenzae type b (Hib) vaccination of children has led to a decline in incidence of Hib disease in young Alaskan children. However, the impact of vaccination on unimmunized Alaskan adolescents and adults has not been studied. OBJECTIVE: To characterize trends in incidence of and mortality due to invasive H influenzae disease in Alaskan residents aged 10 years and older prior to and after the introduction of a statewide Hib infant vaccination program. DESIGN AND SETTING: Population-based, descriptive correlational study conducted 1980-1996 in Alaska. SUBJECTS: One hundred twenty-nine individuals (31 Alaska Natives and 98 nonnative Alaska residents) aged 10 years and older in whom H influenzae was cultured from a normally sterile site. MAIN OUTCOME MEASURES: Incidence of H influenzae infection before (1980-1990) vs after (1991-1996) vaccination program initiation; serotype, biotype, and beta-lactamase production of isolates. RESULTS: The overall annual incidence of invasive H influenzae in those aged 10 years and older declined 33%, from 2.1 per 100,000 persons per year to 1.4 per 100,000 persons per year (P=. 03) after initiation of statewide infant Hib vaccination programs in 1991. This reduction appeared to be the result of a decrease in serotype b disease (82%; P<.001). Infection with other H influenzae serotypes and nontypeable strains increased from 0.5 per 100,000 persons per year to 1.1 per 100,000 persons per year (P=.01). Incidence declined from 4.2 per 100,000 persons per year to 1.2 per 100,000 persons per year in Alaska Natives (P=.005) and from 1.7 per 100,000 persons per year to 1.4 per 100,000 persons per year in nonnative Alaska residents (P=.37). Pneumonia (43%), sepsis (26%), and meningitis (16%) were the most common clinical presentations. Alcohol/drug abuse was comorbid in 15% of patients, while 13% of patients were pregnant women. beta-Lactamase production occurred in 35% of isolates and was stable throughout the surveillance. The overall case-fatality rate was 15%. CONCLUSION: The overall statewide incidence of invasive H influenzae infections in unimmunized persons aged 10 years and older decreased after the initiation of an infant Hib vaccine program, perhaps by decreasing Hib carriage in child reservoirs. An increase in non-serotype b strains was observed. This trend justifies the need for continued surveillance of invasive disease caused by H influenzae. JAMA. 2000.

Elimination of new chronic hepatitis B virus infections: results of the Alaska immunization program.

An immunization assessment and a serologic survey were conducted to evaluate the effectiveness of a hepatitis B immunization program in eliminating hepatitis B virus (HBV) transmission among Alaska Natives in a region in which HBV infection is endemic. Hepatitis B vaccine coverage was 93% among 567 children

Bronchiectasis in Alaska Native children: causes and clinical courses.

Although bronchiectasis has become a rare condition in U.S. children, it is still commonly diagnosed in Alaska Native children in the Yukon Kuskokwim Delta. The prevalence of bronchiectasis has not decreased in persons born during the 1980s as compared with those born in the 1940s. We reviewed case histories of 46 children with bronchiectasis. We observed that recurrent pneumonia was the major preceding medical condition in 85% of patients. There was an association between the lobes affected by pneumonia and the lobes affected by bronchiectasis. Eight (17%) patients had surgical resection of involved lobes. We conclude that the continued high prevalence of bronchiectasis appears to be related to extremely high rates of infant and childhood pneumonia. Pediatr Pulmonol. 2000;29:182-187. Published 2000 Wiley-Liss, Inc.

Associations between dietary factors and plasma lipids related to cardiovascular disease among Siberian Yupiks of Alaska.

The diet of northern Native people has been postulated to protect against cardiovascular disease. We asked whether nutrient and food intakes of Eskimos were correlated with their plasma cholesterol, LDL, HDL, triglycerides and LDL-HDL ratio. Frequency of consumption of 91 foods among 64 Siberian Yupik adults was measured during home-based interviews. Intake of monounsaturated fat by men was negatively correlated with LDL. Foods and nutrients that contribute to the LDL-HDL ratio explained 42% of its variation among all subjects. Inclusion of the body mass index (BMI) explained 59% of the variation in the LDL-HDL ratio. Coefficients were negative for alpha-tocopherol, fresh bird, evaporated milk and cheese, and positive for BMI, syrup and pizza. BMI had a positive effect on the LDL-HDL ratio among younger adults, women and the entire sample, but did not contribute to explaining the variation among older adults or men. This emphasizes the importance of weight control among younger Siberian Yupik women. While coefficients were both positive and negative for traditional and western foods, the presence of traditional foods that were negatively correlated in the regression supports the hypothesis that consumption of traditional foods is important for maintaining cardiovascular health among Siberian Yupiks.

Increases in levels of antibody to hepatitis B surface antigen in an immunized population.

Hepatitis B vaccine is effective in preventing infection with hepatitis B virus (HBV), but its duration of protection is unknown. To examine the effect of exposure to HBV on an immunized population, data were analyzed from a cohort of Alaska Natives who were immunized and then followed up annually for 10 years. A boost in antibody to hepatitis B surface antigen (anti-HBs) was defined as a fourfold rise in levels to > or = 20 mIU/mL that was not accompanied by the presence of antibody to hepatitis B core antigen or attributable to interim vaccination. During 10 years of follow-up, 8.2% of 1,595 vaccines had boosts in anti-HBs. Persons with boosts did not differ significantly from those without boosts in terms of age, gender, village, initial level of anti-HBs, or level of anti-HBs before the boost. These results underscore the continued exposure to HBV among vaccinees and the continued protection against disease that the vaccine provides.

Dietary intakes among Siberian Yupiks of Alaska and implications for cardiovascular disease.

We describe dietary intake for 65 Siberian Yupik residents of Gambell, AK using 24-h recalls and annual food frequencies collected in October 1992. The objectives were to describe dietary characteristics important in risk of cardiovascular disease, determine the extent that their diet differs from the diet of general US and northern populations, assess how the diet met national guidelines for the prevention of cardiovascular disease, and propose dietary recommendations. Compared to US intakes in general (NHANES III), intakes of Siberian Yupiks expressed as percent of energy were: 8-10% higher in fat, 6% higher in protein, 5-7% higher in monounsaturated fats and 12-15% lower in carbohydrate. Energy from saturated and polyunsaturated fats was similar (11% and 8% respectively). Cholesterol intakes were not significantly different. Mean intakes of selenium, a-topocopherol, folacin (men), and vitamin C (men) met Recommended Dietary Allowances, which may contribute to cardiovascular health. Mean intake of n-3 fatty acids (7.0 g/d), twice the 3 g/d associated with favorable effects, was comparable with intake of Greenlandic Eskimos. Dietary risk factors included high intakes of % energy from fat and saturated fat, and low intakes of fiber. Native foods were important sources of monounsaturated fats, n-3 fatty acids and selenium.

Protection provided by hepatitis B vaccine in a Yupik Eskimo population--results of a 10-year study.

A hepatitis B virus vaccine demonstration project was conducted in southwest Alaska in 1981-1982 to determine the immunogenicity and efficacy of the vaccine. A total of 1630 susceptible persons in the Alaskan Native population were vaccinated with the recommended three-dose regimen of plasma-derived hepatitis B vaccine, and 94% demonstrated antibody to hepatitis B surface antigen (anti-HBs) at levels > or = 10 mIU/mL. After 10 years of follow-up, 76% of those immunized had anti-HBs levels > or = 10 mIU. During the 10 years following the first dose of vaccine, 13 study participants developed antibody to hepatitis B core antigen (10 vaccine responders, 3 nonresponders), and none developed sustained HBs positivity or had clinical hepatitis. These data suggest that immunization with hepatitis B vaccine continues to provide high levels of protection from clinical disease for at least 10 years.

Hypertension in Alaska Natives: association with overweight, glucose intolerance, diet and mechanized activity.

OBJECTIVE: Determine the prevalence of hypertension in Alaska Natives and evaluate risk factors. DESIGN: Population-based univariate and multivariate analysis of blood pressure in 1124 Alaska Natives over 20 years of age. RESULTS: The sample had mean: age 45 years, body mass index 27, systolic pressure 123 mmHg and diastolic pressure 73 mmHg. The age-adjusted rate of hypertension > or = 160/95 mmHg was 9.1% and 6.8% among Athabascan Indians and Yup'ik Eskimos, respectively. After controlling for age and sex there was significantly more hypertension among Athabascan Indians (OR = 1.53, CI = 1.07-2.2, p = 0.019) compared to Yup'ik Eskimos. Race was significantly associated with blood pressure > or = 140/90 when controlled for age and overweight (p = 0.01, OR = 0.78, CI = 0.69-0.95). The presence of hypertension was significantly associated with the following: intake of non-indigenous food (p = 0.01); mechanized activities (p = 0.01); and glucose intolerance in both women (p = 0.043) and men (p = 0.001). Multiple regression analysis revealed age (OR = 1.06, CI = 1.05-1.08) and overweight in both men (OR = 3.02, CI = 1.85-4.93) and women (OR = 2.76, CI = 1.81-4.19) to be significantly associated with BP > or = 140/90. CONCLUSION: Hypertension is no longer rare in Alaska Natives and is associated with overweight, non-indigenous diet, mechanized activities, and glucose intolerance.

Dietary change and obesity associated with glucose intolerance in Alaska Natives.

OBJECTIVE: To investigate frequency of food intake, body weight, and glucose intolerance in Alaska Natives. DESIGN: Height, weight, and random blood glucose levels were measured and a frequency-of-food-intake questionnaire was obtained. This questionnaire classified persons as consumers of indigenous foods or nonindigenous foods within three food groups. Those with a random blood glucose measurement > or = 6.72 mmol/L received an oral glucose tolerance test. SETTING: Community screening in 15 villages in Alaska. SUBJECTS: Nutrition screenings were done for 1,124 Alaska Native residents aged 20 years or older. An oral glucose tolerance test was done for 202 subjects. OUTCOMES MEASURED: Subjects were classified as consumers of indigenous or nonindigenous foods within three food groups. A diagnosis of non-insulin-dependent diabetes mellitus (NIDDM) was made on the basis of World Health Organization criteria. A determination of overweight was made on the basis of National Center for Health Statistics criteria. STATISTICAL ANALYSIS: A chi 2 test with Yates correction, t test, and linear regression, with two-sided P values. RESULTS: Athabascan Indians had twice the rate of NIDDM as Yup'ik Eskimos with significantly higher frequency of nonindigenous food intake, plus lower frequency of indigenous carbohydrate and fat intake. Subjects < or = 30 years old consumed significantly more nonindigenous protein and fat and low-nutrient-density carbohydrates than those > or = 60 years old. Persons who had glucose intolerance reported significantly greater consumption of nonindigenous protein and less seal oil. Incidence of overweight was significantly higher than was found 25 years ago. Participants with glucose intolerance were significantly more overweight than others. CONCLUSION: A pattern of increased frequency of nonindigenous protein, low-nutrient-density carbohydrate, and fat intake with less indigenous carbohydrate and fat consumption was found in subjects < or = 30 years old and in association with the higher rate of NIDDM found in the Athabascan Indians. Persons with glucose intolerance were significantly more overweight than others. APPLICATIONS: Although the nutritional value of indigenous foods for reducing disease risk should be promoted, nutrition education, especially among young adults, should also include building skills to select and prepare nonindigenous foods to attain a healthful diet. Although snacking is a concern, dietary fat was the most significant factor in obesity and NIDDM.

Hospitalizations for respiratory syncytial virus infection in Alaska Native children.

To characterize the epidemiology of Alaska Native children hospitalized for respiratory syncytial virus infections, we reviewed records of hospitalizations during the winter seasons of 1991 to 1992 and 1992 to 1993 at a hospital in Anchorage and a rural hospital in the Yukon Kuskokwim Delta (YKD) region of southwestern Alaska. The median age of hospitalization for respiratory syncytial virus infection was 2 months of age for YKD residents and 4.5 months for Anchorage residents. Sixteen percent of the hospitalized YKD children were less than 1 month of age, whereas the same was true for only 3% of the Anchorage children. Eight percent of the YKD patients required mechanical ventilation, whereas none of the Anchorage patients required ventilation. The median hospital stay was 4.8 days for YKD patients and 3.2 days for Anchorage patients. Hospitalization rates for infants less than 1 year of age were 33/1000 for Alaska Natives in Anchorage and 100/1000 for those in the YKD region. The extremely high hospitalization rate, especially among very young infants in the rural YKD region, points to a need for early preventive efforts.

Immunogenicity of pneumococcal revaccination in patients with chronic disease.

BACKGROUND: To prevent serious pneumococcal infections, 23-valent pneumococcal polysaccharide vaccine is recommended for individuals over 24 months of age with chronic predisposing diseases and for healthy older adults. This nonrandomized controlled study in rural Alaska assessed the immunogenicity of revaccination in adults. METHODS: Twenty-six adults, 33 to 88 years of age, vaccinated a mean of 7.4 years before this study, were matched to 26 previously unvaccinated subjects by age, number of chronic diseases, sex, and ethnicity. One or more chronic diseases were validated in 62% of subjects (32 of 52). All received a first or second intramuscular dose of pneumococcal vaccine. Antibody levels were determined by radioimmunoassay for 12 pneumococcal capsular serotypes immediately before and 20 to 84 days after vaccination. RESULTS: Six to 9 years after primary vaccination, over one third of serotype-specific antibody levels were below 500 ng of antibody nitrogen per milliliter, equal to the percentage in unvaccinated subjects of similar age. Antibody levels against all pneumococcal serotypes rose to similar levels after primary vaccination and revaccination, and 54% and 55%, respectively, of subjects who received primary vaccination and revaccination had at least a 1.4-fold increase in antibody levels. Only the antibody level for serotype 4 remained low. Neither gender nor age affected peak response. For those with chronic diseases, there was a trend toward fewer low antibody levels against three or more serotypes after revaccination (two subjects [13%]) than after primary vaccination (five subjects [31%]). CONCLUSIONS: Following the initial immunization of high-risk and elderly patients with pneumococcal polysaccharide, pneumococcal antibody levels appear to wane with time. Primary vaccination and revaccination 6 or more years after a first dose of pneumococcal vaccine stimulate comparable mean antibody levels.