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Biomedical subjects

K L Nichol

Publications and source records attributed to K L Nichol.

At least 19 recordsLinked to original sources
PubMed2006

Burden of upper respiratory illnesses among college and university students: 2002-2003 and 2003-2004 cohorts.

Upper respiratory illnesses, including colds and influenza-like illnesses, are common among college and university students. We have established an ongoing, serial cohort study to assess the occurrences of these illnesses among college and university students as well as the impact of these illnesses on overall health, school and work performance, and health care use. In this paper we report on the first 2 years of this study (2002-2003 and 2003-2004). For each year, more than 4000 students responded to the e-mail invitations to participate, and they provided more than 3000 person-seasons of follow-up information during the monthly surveys conducted November-April. In both years, colds and influenza-like illnesses were common and associated with significant numbers of bed days, reduced activity days, school and work loss, impaired school performance, and increased health care utilization. Efforts to prevent upper respiratory illnesses among college and university students could improve their health and reduce health care utilization during the winter months.

Cohort Studies↗
PubMed2006

Do recommended high-risk adults benefit from a first influenza vaccination?

It is unknown whether a first influenza vaccination protects high-risk adults from severe morbidity and mortality during influenza epidemics. As part of the PRISMA nested case-control study, we aimed to evaluate the effectiveness of first-time and repeat influenza vaccinations in adult persons recommended for vaccination aged between 18 and 64 years during the 1999-2000 influenza A epidemic. After adjustments, 69% of hospitalizations for acute respiratory or cardiovascular disease or death were prevented in first-time vaccinees (95% percent confidence interval [95% CI]: 8-90%). The corresponding figure in persons who were vaccinated before was 85% (95% CI: 36-96%). Adult persons with high-risk medical conditions can substantially benefit from a first and repeat influenza vaccination prior to an epidemic.

Adult↗
PubMed2005

Influence of clinical outcome and outcome period definitions on estimates of absolute clinical and economic benefits of influenza vaccination in community dwelling elderly persons.

Studies assessing the clinical and economic benefits of vaccination in the elderly have used different clinical outcomes (e.g. hospitalizations for pneumonia or influenza versus hospitalizations for respiratory and cardiovascular causes) and different outcome periods (e.g. peak versus total influenza season) on which to base estimates of clinical effectiveness and cost effectiveness. We explored the implications of these varying approaches by comparing two health economic analysis models of influenza vaccination of community-dwelling elderly persons. We developed computerized models using clinical data from 3 large US HMOs for the 1998-1999 and 1999-2000 influenza seasons. The primary health economic model used a broad definition of clinical events and outcome period and included hospitalizations for all respiratory and cardiovascular events that occurred during the entire influenza season. The alternative model used more restrictive definitions and included pneumonia or influenza hospitalizations occurring during the peak influenza season. The results of Monte Carlo simulation showed that, with the more inclusive primary model, influenza vaccination resulted in net medical care cost savings due to fewer respiratory or cardiovascular hospitalizations of Dollars 71/person vaccinated (5th-95th percentile Dollars 32-118) and net savings of Dollars 809/year of life saved (5th-95th percentile Dollars 331-1450). In contrast, the alternate model found costs of Dollars 3.50/person vaccinated (5th-95th percentile Dollars -11 to 5) and net costs of Dollars 91/year of life saved (5th-95th percentile Dollars -309 to 126). Our findings confirm that influenza vaccination of the elderly is most likely cost saving and supports policies and programs that advocate routine immunization of all persons 65 and older. They also highlight how different outcome definitions can influence the results of health economic analyses.

Aged↗
PubMed2004

A nested case-control study of influenza vaccination was a cost-effective alternative to a full cohort analysis.

OBJECTIVE: In the absence of trial results that are applicable to the target population, nested case-control studies might be an alternative to full-cohort analysis. We compared relative and absolute estimates of associations in an influenza vaccine study using both designs. STUDY DESIGN AND SETTING: Data from elderly persons enrolled during six consecutive influenza seasons were used (147,551 person-periods). The endpoints "hospitalization for pneumonia or influenza" (P&I) or "death" were used combined and separately to define three types of cases. Controls for the case-control samples were randomly selected from the remainder of the total cohort at different ratios (1:1 to 1:4). Logistic regression analysis was used to assess adjusted vaccine effectiveness (VE). Sampling fractions were used to determine the number needed to treat to prevent one outcome. Receiver-operator-curve analysis was conducted to estimate the area under the curve (AUC) as a measure of discriminative capacity of the prognostic model. RESULTS: In all, 978 P and I hospitalizations and 1,339 deaths were observed. The adjusted estimates of relative estimates (VE, AUC) and their corresponding 95% confidence intervals were virtually the same using both study designs, notably when the case-control ratio was high (1:4). CONCLUSION: A nested case-control design can provide valid and precise estimates of associations and is a cost-effective alternative for full-cohort analysis.

Aged↗
PubMed2002

Confounding by indication in non-experimental evaluation of vaccine effectiveness: the example of prevention of influenza complications.

Randomised allocation of vaccine or placebo is the preferred method to assess the effects of the vaccine on clinical outcomes relevant to the individual patient. In the absence of phase 3 trials using clinical end points, notably post-influenza complications, alternative non-experimental designs to evaluate vaccine effects or safety are often used. The application of these designs may, however, lead to invalid estimates of vaccine effectiveness or safety. As patients with poor prognosis are more likely to be immunised, selection for vaccination is confounded by patient factors that are also related to clinical end points. This paper describes several design and analytical methods aimed at limiting or preventing this confounding by indication in non-experimental studies. In short, comparison of study groups with similar prognosis, restriction of the study population, and statistical adjustment for dissimilarities in prognosis are important tools and should be considered. Only if the investigator is able to show that confounding by indication is sufficiently controlled for, results of a non-experimental study may be of use to direct an evidence based vaccine policy.

Adult↗
PubMed2001

Live attenuated influenza virus vaccines: new options for the prevention of influenza.

Live attenuated influenza virus (LAIV) vaccines present new possibilities for the prevention and control of influenza. Administered intranasally, LAIV vaccines offer a needle-free route of administration. These investigational vaccines have also been shown to be safe and effective in children and healthy working adults. A 2-year placebo-controlled trial among young children (1996-1997 and 1997-1998 influenza seasons) demonstrated that LAIV vaccine was associated with a 92% reduction in laboratory-confirmed cases of influenza. Vaccination also significantly reduced episodes of otitis media and antibiotic use. In a placebo-controlled trial among healthy working adults during the 1997-1998 season, LAIV vaccine significantly reduced episodes of febrile upper respiratory tract illness and illness-associated work loss, health-care use, and antibiotic use. Seventy percent of study participants self-administered the vaccine. An economic analysis of the benefits of LAIV vaccine in this population suggests that the break-even cost for LAIV vaccine and its administration for healthy working adults would be about $39. For both children and healthy adults, LAIV vaccine provided substantial protection during the 1997-1998 season when the predominant circulating virus, the A/Sydney variant, was not contained in the vaccine. Studies are still underway to evaluate the potential incremental benefits of LAIV vaccine in addition to inactivated vaccine in high-risk populations. LAIV vaccines will be an important addition to the armamentarium for fighting influenza.

Clinical Trials, Phase I as Topic↗
PubMed2001

Influenza vaccine effectiveness in preventing hospitalizations and deaths in persons 65 years or older in Minnesota, New York, and Oregon: data from 3 health plans.

This study developed methods and determined the impact of influenza vaccination on elderly persons in 3 large health plans: Kaiser Permanente Northwest, HealthPartners, and Oxford Health Plans. Data for the 1996-1997 and 1997-1998 seasons were extracted from administrative databases. Subjects were health plan members > or = 65 years old. Comorbid conditions collected from the preceding year were used for risk adjustment with logistic regression. The virus-vaccine match was excellent for year 1 and fair for year 2. Both years, during peak and total periods, vaccination reduced all causes of death and hospitalization for pneumonia and influenza: hospitalizations were reduced by 19%-20% and 18%-24% for years 1 and 2, respectively, and deaths were reduced by 60%-61% and 35%-39% for the same periods. These results show that all elderly persons should be immunized annually for influenza. The methods used in this study are an efficient cost-effective way to study vaccine impact and similar questions.

Age Factors↗
PubMed2001

Cost-benefit analysis of a strategy to vaccinate healthy working adults against influenza.

BACKGROUND: Influenza is a major cause of illness, disruption to daily life, and work absenteeism among healthy working adults aged between 18 and 64 years. This group is not included among the traditional priority groups for annual vaccination. Immunization rates remain low. OBJECTIVE: To assess the economic implications of a strategy for annual vaccination of this group. METHODS: Using the societal perspective, this cost-benefit analysis included the direct and indirect costs associated with vaccination as well as the direct and indirect costs prevented by vaccination. Clinical and economic variable estimates were derived primarily from the published literature. For this model, it was assumed that vaccination occurred in efficient, low-cost settings such as at the work site. Monte Carlo simulation was used to calculate the mean net costs or savings along with the 95% probability interval, and sensitivity analyses explored the sensitivity of the cost model to different values of the input variables. RESULTS: Vaccinating healthy working adults was on average cost saving, with mean savings of $13.66 per person vaccinated (95% probability interval: net savings of $32.97 to net costs of $2.18), with vaccination generating net savings 95% of the time. The model was most sensitive to the influenza illness rate, the work absenteeism rate due to influenza, and hourly wages. In the worst-case scenario vaccination was not cost saving. Vaccination also generated net costs to society during years with a poor vaccine-circulating virus strain match. In all of the other sensitivity analysis scenarios, vaccination was cost saving. CONCLUSION: Influenza vaccination of healthy working adults on average is cost saving. These findings support a strategy of routine, annual vaccination for this group, especially when vaccination occurs in efficient and low-cost sites.

Adult↗
PubMed2001

Excess mortality due to pneumonia or influenza during influenza seasons among persons with acquired immunodeficiency syndrome.

BACKGROUND: Anecdotal reports suggest that influenza-related morbidity may be high among persons with acquired immunodeficiency syndrome (AIDS), but little information is available concerning the population-level impact of influenza on mortality in persons with AIDS. METHODS: Using the Multiple Cause-of-Death data files, which contain information on all deaths occurring in the United States each year, we calculated the numbers of excess deaths and rates of excess death due to pneumonia or influenza among persons with AIDS aged 13 years and older during the influenza seasons 1991-1992 through 1993-1994. For comparison, numbers of excess deaths and excess death rates were also calculated for several other groups including the general US population aged 13 years and older and the general US population aged 65 years and older. RESULTS: During the 1991-1992, 1992-1993, and 1993-1994 influenza seasons, there were 261, 254, and 191 excess deaths due to pneumonia or influenza in persons with AIDS and excess death rates of 19.74, 15.38, and 10.17 deaths per 10 000 persons, respectively, compared with a summer baseline period. For the same seasons, we observed excess death rates of 1.40, 1.62, and 1.48 for the general US population aged 13 years and older and 8.10, 9.28, and 8.54 for the general US population aged 65 years and older. Thus, persons with AIDS had excess death rates substantially higher than the general US population and similar to, if not somewhat higher than, the general US population aged 65 years and older, a group that is already targeted for annual vaccination. The findings were similar when we compared the preinfluenza season with the influenza season. CONCLUSIONS: Persons with AIDS have significant excess mortality due to pneumonia or influenza during influenza seasons and should be considered a high-risk group that is targeted for the prevention of influenza.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Immune function and vaccine responses in healthy advanced elderly patients.

BACKGROUND: Decline in immune function has been reported to predictably accompany advancing age. However, to our knowledge, few studies have specifically characterized the rapidly expanding advanced elderly population or controlled adequately for concurrent diseases. OBJECTIVE: To assess whether successfully reaching an advanced age in good health is associated with preserved immune function. METHODS: We prospectively compared in vivo with in vitro variables of immune function in 29 healthy, independently living elderly subjects (mean age, 80 years; age range, 75-103 years) and in 21 healthy young control subjects (mean age, 29 years; age range, 25-35 years) in a Veterans Affairs Medical Center. RESULTS: In vivo, among elderly and young subjects, numbers of total white blood cells, monocytes, lymphocytes, and lymphocyte subsets (CD4(+) and CD8(+) T lymphocytes and CD20(+) B cells) were similar, as were levels of total serum IgG and IgM. Only levels of serum IgA were higher in the elderly subjects (3.0 vs 1.7 g/L; P=.001). Functionally, both groups showed vigorous responses to protein (tetanus and diphtheria toxoids) and polysaccharide (23-valent pneumococcal) vaccines. Although levels varied, the fold increases in vaccine antigen-specific IgG were not significantly different in young and elderly subjects, and the avidities of IgG to pneumococcal polysaccharides 14 and 19F were similar before and after vaccination. In vitro, proliferative responses of blood mononuclear cells to T-lymphocyte and B-cell mitogens (pokeweed mitogen, Staphylococcus aureus Cowan strain I, and S aureus Cowan strain I plus interleukin 2), and lipopolysaccharide-induced production of tumor necrosis factor alpha, were comparable in elderly vs young subjects. CONCLUSION: Successful aging, defined by reaching an advanced age with one's overall health intact, may be associated with preserved immune function and adequate responses to vaccines.

Adult↗
PubMed1999

The health and economic benefits associated with pneumococcal vaccination of elderly persons with chronic lung disease.

BACKGROUND: More than 50% of the elderly population has not received pneumococcal vaccination. Uncertainty regarding the benefits of immunization, particularly for noninvasive disease, may contribute to the underuse of pneumococcal vaccine. OBJECTIVE: To assess the health and economic benefits associated with pneumococcal vaccination. METHODS: We conducted a 2-year retrospective cohort study among all elderly members of a staff-model managed care organization who had a baseline diagnosis of chronic lung disease. The study outcomes were assessed over 2 years, from November 15, 1993, through November 14, 1995, and included hospitalizations for pneumonia and influenza, death, and hospitalization costs. Using administrative data, we compared these outcomes for vaccinated and unvaccinated subjects using multivariate models to control for subjects' baseline demographic and health characteristics. The additive benefits of combined influenza and pneumococcal vaccination were also assessed for the 2 influenza seasons included in the study. RESULTS: There were 1898 subjects. Pneumococcal vaccination was associated with significantly lower risks for pneumonia hospitalizations (adjusted risk ratio [RR], 0.57; 95% confidence interval [CI], 0.38-0.84; P=.005) and for death (adjusted RR, 0.71; 95% CI, 0.56-0.91; P = .008). For the control outcome of all nonpneumonia hospitalizations, rates did not differ significantly between the 2 groups (adjusted RR, 0.91; 95% CI, 0.77-1.07; P= .24). During the influenza seasons included in the study, the benefits of pneumococcal and influenza vaccinations were additive, with an adjusted RR of 0.28 (95% CI, 0.14-0.58; P<.001) for the number of hospitalizations for pneumonia and influenza among persons who had received both vaccinations compared with those who had received neither and an adjusted odds ratio of 0.18 (95% CI, 0.11-0.31; P<.001) for death. Over the 2-year outcome period, pneumococcal vaccination was also associated with direct medical care cost savings. CONCLUSIONS: Pneumococcal vaccination of elderly persons with chronic lung disease was associated with fewer hospitalizations for pneumonia, fewer deaths, and direct medical care cost savings.

Aged↗
PubMed1999

Complications of influenza and benefits of vaccination.

Uncertainty regarding the benefits of influenza vaccination may contribute to the underutilization of this vaccine. We have conducted serial cohort studies using the administrative data bases of a Twin Cities based managed care organization to assess the impact of disease and benefits of vaccination among the elderly. For the 6 seasons 1990-1991 through 1995-1996, there were more than 20,000 elderly members of the health plan included in each cohort. Data collected included information on baseline demographic and health characteristics, vaccination status and outcomes (hospitalizations and death). Multivariate regression techniques were used to compare the risks of outcomes between vaccinated and unvaccinated persons while controlling for covariates and confounders. Results for data pooled over the 6 seasons demonstrated that influenza vaccination was associated with significant reductions in hospitalizations, outpatient visits, and death among the elderly. Similar findings were observed for low, intermediate, and high risk subgroups. Vaccination was also associated with cost savings. These findings are consistent with results from studies conducted in other countries and over other seasons and strongly support age-based recommendations for annual influenza vaccination for all persons ages 65 and over.

Aged↗
PubMed1999

The additive benefits of influenza and pneumococcal vaccinations during influenza seasons among elderly persons with chronic lung disease.

Uncertainty regarding the benefits of pneumococcal vaccination may contribute to the under use of this vaccine. The present study was conducted to clarify the benefits of influenza and pneumococcal vaccinations during 3 influenza seasons among elderly persons with chronic lung disease. All elderly members of a large managed care organization with a prior diagnosis of chronic lung disease were included in a cohort that was followed over three influenza seasons (1993-1994, 1994-1995, and 1995-1996). Data obtained from the administrative data bases of the health care organization included baseline demographic and health characteristics, influenza vaccination status for each season, date of pneumococcal vaccination, and outcomes for each season including hospitalization for pneumonia and death. Cox proportional hazards regression and Poisson regression with repeated measures were used to compare the risk of outcomes among vaccinated and unvaccinated persons while controlling for covariates and confounders. During the three influenza seasons, influenza vaccination alone was associated with a 52% reduction (95% CI 18-72) in hospitalizations for pneumonia and a 70% reduction (95% CI 57-89) in death. Pneumococcal vaccination alone during the three influenza seasons was associated with a 27% reduction (95% CI 13-52) in hospitalizations for pneumonia and a 34% reduction (95% CI 6-54) in death. Both vaccinations together demonstrated additive benefits. When both vaccinations had been received, there was a 63% reduction (95% CI 29-80) in hospitalizations for pneumonia and an 81% reduction (95% CI 68-88) in death versus when neither had been received. These findings suggest pneumococcal vaccination is associated with substantial benefits for elderly persons with chronic lung disease.

Aged↗
PubMed1999

Effectiveness of live, attenuated intranasal influenza virus vaccine in healthy, working adults: a randomized controlled trial.

CONTEXT: Influenza virus is a major cause of illness, disruption to daily life, and increased use of health care in all age groups. OBJECTIVE: To assess the safety and effectiveness of intranasally administered trivalent, live, attenuated influenza virus (LAIV) vaccine for reducing illness, absenteeism, and health care use among healthy, working adults. DESIGN: Randomized, double-blind, placebo-controlled trial conducted from September 1997 through March 1998. SETTING: Thirteen centers across the United States. PARTICIPANTS: A total of 4561 healthy, working adults aged 18 to 64 years recruited through health insurance plans, at work sites, and from the general population. INTERVENTION: Participants were randomized 2:1 to receive intranasally administered trivalent LAIV vaccine (n = 3041) or placebo (n = 1520) in the fall of 1997. MAIN OUTCOME MEASURES: Episodes of febrile illness, severe febrile illness, febrile upper respiratory tract illness, work loss, and health care use during the peak and total influenza outbreak periods, and adverse events. RESULTS: Recipients of LAIV vaccine were as likely to experience 1 or more febrile illnesses as placebo recipients during peak outbreak periods (13.2% for vaccine vs 14.6% for placebo; P=.19). However, vaccination significantly reduced the numbers of severe febrile illnesses (18.8% reduction; 95% confidence interval [CI], 7.4%-28.8%) and febrile upper respiratory tract illnesses (23.6% reduction; 95% CI, 12.7%-33.2%). Vaccination also led to fewer days of illness across all illness syndromes (22.9% reduction for febrile illnesses; 27.3% reduction for severe febrile illnesses), fewer days of work lost (17.9% reduction for severe febrile illnesses; 28.4% reduction for febrile upper respiratory tract illnesses), and fewer days with health care provider visits (24.8% reduction for severe febrile illnesses; 40.9% reduction for febrile upper respiratory tract illnesses). Use of prescription antibiotics and over-the-counter medications was also reduced across all illness syndromes. Vaccine recipients were more likely to experience runny nose or sore throat during the first 7 days after vaccination, but serious adverse events between the groups were not significantly different. The match between the type A(H3N2) vaccine strain and the predominant circulating virus strain (A/Sydney/05/97[H3N2]) for the 1997-1998 season was poor, suggesting that LAIV provided substantial cross-protection against this variant influenza A virus strain. CONCLUSION: Intranasal trivalent LAIV vaccine was safe and effective in healthy, working adults in a year in which a drifted influenza A virus predominated.

Administration, Intranasal↗
PubMed1999

Relation between influenza vaccination and outpatient visits, hospitalization, and mortality in elderly persons with chronic lung disease.

BACKGROUND: Influenza vaccine is underused in groups targeted for vaccination. OBJECTIVE: To define the effects of influenza and the benefits of influenza vaccination in elderly persons with chronic lung disease. DESIGN: Retrospective, multiseason cohort study. SETTING: Large managed care organization. PATIENTS: All elderly members of a managed care organization who had a previous diagnosis of chronic lung disease. MEASUREMENTS: Outcomes in vaccinated and unvaccinated persons for the 1993-1994, 1994-1995, and 1995-1996 influenza seasons were compared after adjustment for baseline demographic and health characteristics. All data were obtained from administrative databases. RESULTS: Vaccination rates were greater than 70% for each season. Among unvaccinated persons, hospitalization rates for pneumonia and influenza were twice as high in the influenza seasons as they were in the interim (noninfluenza) periods. Influenza vaccination was associated with fewer hospitalizations for pneumonia and influenza (adjusted risk ratio, 0.48 [95% CI, 0.28 to 0.82]) and with lower risk for death (adjusted odds ratio, 0.30 [CI, 0.21 to 0.43]) during the influenza seasons. It was also associated with fewer outpatient visits for pneumonia and influenza and for all respiratory conditions. CONCLUSIONS: For elderly persons with chronic lung disease, influenza is associated with significant adverse health effects and influenza vaccination is associated with substantial health benefits, including fewer outpatient visits, fewer hospitalizations, and fewer deaths. Health care providers should take advantage of all opportunities to immunize these high-risk patients.

Age Factors↗