Is vaccination against measles, mumps, and rubella associated with reduced rates of antibiotic treatments among children below the age of 2 years? Nationwide register-based study from Denmark, Finland, Norway, and Sweden

OBJECTIVES

Previous studies have shown that vaccination against measles, mumps, and rubella (MMR) may have beneficial non-specific effects, reducing the risk of infections not targeted by the vaccine. We investigated if MMR vaccine given after the third dose of diphtheria-tetanus-acellular pertussis vaccine (DTaP3), was associated with reduced rates of antibiotic treatments.

METHODS

Register-based cohort study following children from the age of recommended MMR vaccination until age 2 years. We included 831,287 children born in Denmark, Finland, Norway, and Sweden who had received DTaP3 but not yet MMR vaccine. Cox proportional hazards regression with age as the underlying timescale and vaccination status as a time-varying exposure was used to estimate covariate-adjusted Hazard Ratios (aHRs) and inverse probability of treatment weighted (IPTW) HRs of antibiotic treatments. Summary estimates were calculated using random-effects meta-analysis.

RESULTS

Compared with only having received DTaP3, receipt of MMR vaccine after DTaP3 was associated with reduced rates of antibiotic treatments in all countries: the aHR was 0.92 (0.91-0.93) in Denmark, 0.92 (0.90-0.94) in Finland, 0.84 (0.82-0.85) in Norway, and 0.87 (0.85-0.90) in Sweden, yielding a summary estimate of 0.89 (0.85-0.93). A stronger beneficial association was seen in a negative control exposure analysis comparing children vaccinated with DTaP3 vs two doses of DTaP.

CONCLUSIONS

Across the Nordic countries, receipt of MMR vaccine after DTaP3 was associated with an 11% lower rate of antibiotic treatments. The negative control analysis suggests that the findings are affected by residual confounding. Findings suggest that potential non-specific effects of MMR vaccine are of limited clinical and public health importance for the milder infections treated out-of-hospital in the Nordic setting.

The coverage of influenza vaccination and predictors of influenza non-vaccination in Danish cancer patients: A nationwide register-based cohort study

BACKGROUND

Influenza vaccination is recommended and provided free-of-charge to Danish citizens aged ≥65 years and to individuals with acquired immunodeficiency. We aimed to estimate influenza vaccination coverage and investigate predictors of influenza non-vaccination in Danish cancer patients.

METHODS

A nationwide cohort study of all Danish citizens aged ≥18 years with an incident cancer diagnosis between 2002 and 2017. Using national registries, we assessed information on influenza vaccination and potential predictors of influenza non-vaccination. We estimated adjusted prevalence ratios (aPR) of influenza non-vaccination for patients aged <65 years and ≥65 years.

RESULTS

We observed 269,863 patients during 840,876 influenza vaccination seasons. The influenza vaccination coverage was 14 % for cancer patients <65 years and 51 % for those ≥65 years. No influenza vaccination in the previous season was associated with non-vaccination in the current season (<65 years: aPR = 2.75, 95 %CI = 2.71-2.80; ≥65 years: aPR = 5.15, 95 %CI = 5.10-5.21). Haematological cancer patients receiving chemotherapy had lower vaccination prevalence compared with those not receiving chemotherapy.

CONCLUSIONS

The influenza vaccination coverage was low among cancer patients. Influenza non-vaccination in the previous season was the strongest predictor of not receiving influenza vaccination in the current season. Haematological cancer patients on current chemotherapy had lower vaccination prevalence than those not currently receiving chemotherapy.

Cohort Profile: Childhood morbidity and potential non-specific effects of the childhood vaccination programmes in the Nordic countries (NONSEnse): register-based cohort of children born 1990-2017/2018

PURPOSE

The aim of the NONSEnse project is to investigate the non-specific effects of vaccines and immunisation programmes on the overall health of children by using information from the extensive nationwide registers on health and sociodemographic factors in Denmark, Finland, Norway and Sweden.

PARTICIPANTS

The cohort covers 9 072 420 children aged 0-17 years, born 1990-2017/2018 and living in Denmark, Finland, Norway or Sweden. All countries use a unique identification number for its permanent residents, which makes it possible to link individual-level information from different registers.

FINDINGS TO DATE

Data collection and harmonisation according to a common data model was completed in March 2022. As a prerequisite for comparing the effects of childhood vaccinations on the overall health of children across the Nordic countries, we have identified indicators measuring similar levels of infectious disease morbidity across these settings. So far, studies pertaining to non-specific effects of vaccines are limited to investigations that could be undertaken using aggregated data sets that were available before the NONSEnse cohort with individual-level information was completely set up.

FUTURE PLANS

We are currently performing several studies of the effects on non-targeted infectious disease morbidity across the countries following vaccination against measles, mumps, rubella, diphtheria, tetanus, pertussis, human papillomavirus, rotavirus and influenza. Multiple studies are planned within the next years using different study designs to facilitate triangulation of results and enhance causal inference.

REGISTRATION

No clinical trials will be conducted within the NONSEnse project.

Trends in Antibiotic Use in Danish, Finnish, Norwegian and Swedish Children

Objective

To compare the use of antibiotics in children in four Northern European countries.

Methods

We conducted a register-based study based on individual-level prescription data from national prescription registers. We identified all redeemed outpatient prescriptions for systemic antibiotics in children aged 0–14 years from July 2006 to June 2017 in Denmark, Finland, Norway, and Sweden. We computed incidence rates and incidence rate ratios of treatment episodes with any antibiotic and different antibiotic classes.

Results

In 2016/2017, the rates of antibiotic treatment episodes per 1000 person-years in children aged 0–14 years were 429, 284, 219, and 184 in Finland, Denmark, Sweden, and Norway, respectively, and the rate ratios (95% confidence intervals) compared with Norway were 2.33 (2.33–2.34), 1.54 (1.54–1.55), and 1.19 (1.19–1.20) in Finland, Denmark, and Sweden, respectively. The rate of antibiotic treatment episodes declined over time in all countries. The relative reductions in 2016/2017 compared with 2006/2007 were 36% in Finland, 40% in Denmark, 49% in Sweden, and 29% in Norway. Treatment episodes peaked between age 12 and 18 months. The most used antibiotic class was beta-lactamase sensitive penicillins among all children in Norway and Sweden and among children above two years in Denmark, while penicillins with extended spectrum were most used in Finland and among the youngest children in Denmark.

Conclusion

In all countries, the use of antibiotics in children declined between 2006 and 2017. However, there were still considerable differences in antibiotic use between otherwise quite similar Nordic countries, with a more than 2-fold difference between the countries with the lowest and highest rates. Interventions to reduce the number of antibiotic treatment episodes in the countries with higher rates could reduce the total antibiotic use.

Hospital Contacts for Infectious Diseases Among Children in Denmark, Finland, Norway, and Sweden, 2008-2017

Purpose

Comparing rates of childhood infectious disease hospitalisations across countries may uncover areas for improvement in the prevention of severe childhood infections. We compared rates of childhood infectious disease hospital contacts across Denmark, Finland, Norway, and Sweden with the overall objective to elucidate potential differences in burden of disease and in organisational and registration practices.

Methods

Using national registries, we estimated incidence rates for infectious disease hospital contacts between 2008 and 2017 among children aged 0–14 years. We investigated the rates for different types of contacts (inpatient or outpatient including emergency room), duration of admission, and by sex.

Results

During the study period, the rate of all hospital contacts per 1000 person-years was highest in Sweden (125.2) followed by Finland (87.1), Denmark (79.0), and Norway (62.1). The rates aligned for inpatient contacts with overnight stays; 19.3 (Denmark), 16.6 (Finland), 16.3 (Norway), and 13.0 (Sweden); these were highest in early infancy in all countries. A peak around 1 year of age was seen in all countries except in Sweden. The rates were higher among boys compared with girls in early childhood, after 13 years of age the rates among girls surpassed the boys.

Conclusion

Large cross-country differences were observed for outpatient and short-term hospital contacts for infectious diseases, affected by differences in organisational structures and coding practices across and within countries over time. Inpatient contacts requiring overnight stays reflected more comparable levels of severe infections across countries. Childhood infectious disease morbidity was greatest among boys and before 2 years of age.

Identifying Valid Algorithms for Number of Lines of Anti-Neoplastic Therapy in the Danish National Patient Registry Among Patients with Advanced Ovarian, Gastric, Renal Cell, Urothelial, and Non-Small Cell Lung Cancer Attending a Danish University Hospital

Purpose

To develop algorithms to identify number of lines of anti-neoplastic therapy per patient based on the Danish National Patient Registry (DNPR) and identify which algorithm has the highest percentage agreement with a reference standard of documentation in medical records.

Patients and Methods

We included 179 patients diagnosed between January 1, 2012, and December 31, 2016, with stage II, III, or IV urothelial cell carcinoma or stage III or IV epithelial ovarian cancer, gastric adenocarcinoma, renal cell carcinoma, or non-small cell lung cancer (NSCLC). We developed two algorithms for number of lines of anti-neoplastic therapy based on dates and treatment codes (eg, “treatment with cisplatin” or “cytostatic treatment”) in the DNPR. First, to denote a change in line of therapy the “Time-based algorithm” used the number of days between consecutive administrations. Second, the “Drug-based algorithm” used information on drug names if available or the number of days between consecutive administrations if no drug names were specified. We calculated the percentage agreement between the algorithms setting the number of allowed days between consecutive administrations from 28 to 50 and the reference standard – information on anti-neoplastic therapy drugs abstracted from medical records and subsequently coded according to lines of anti-neoplastic therapy.

Results

For the “Time-based algorithm”, the highest percentage agreement with the reference standard was found when using <45 days between consecutive administrations (67.6%; 95% CI: 60.1–73.8%). However, the percentage agreement was higher for the “Drug-based algorithm” using <45 days between consecutive administrations for registrations where the drug name was unspecified (90.5%; 95% CI: 85.0–93.7%).

Conclusion

The algorithm for number of lines of anti-neoplastic therapy that had the highest percentage agreement with the reference standard (medical records) incorporated both registration of specific drug names and <45 days between consecutive administrations if the drug name was unspecified in routinely recorded data from DNPR.

Treatment and Survival in Advanced Non-Small Cell Lung Cancer, Urothelial, Ovarian, Gastric and Kidney Cancer: A Nationwide Comprehensive Evaluation

Purpose

Few studies have described real-world treatment patterns and survival before the widespread use of immune checkpoint inhibitors (ICIs). We aimed to describe anti-cancer treatment including the use of programmed cell death-1 and ligand-1 (PD-1/PD-L1) ICIs and overall survival (OS) in advanced cancer patients as a benchmarking real-world standard before widespread use of ICIs.

Patients and Methods

Using nationwide Danish medical registries, we assembled cohorts of Danish patients with advanced non-small cell lung cancer (NSCLC) (n=12,283), urothelial carcinoma (n=2504), epithelial ovarian cancer (n=1466), gastric adenocarcinoma (n=1457), and renal cell carcinoma (RCC) (n=1261) diagnosed between 1/1/2013 and 31/12/2017. We describe anti-cancer treatment and OS using proportions, medians, and Kaplan-Meier methods.

Results

Between 9% (ovarian cancer) and 25% (gastric adenocarcinoma) of patients did not receive anti-cancer treatment. The remaining patients received surgery, radiation therapy, and/or medical therapy. Chemotherapy was the most frequent medical therapy in all cohorts except for RCC (tyrosine kinase inhibitors). PD-L1/PD-1 ICIs were used in 7-8% of the NSCLC and RCC cohorts-mainly as second or higher line treatments. OS was longest in patients starting treatment with surgery (eg 25.6 months [95%-confidence interval (CI)=21.9-29.4] for NSCLC and 21.4 months [95%-CI=19.8-23.5] for urothelial carcinoma) and shortest for radiation therapy (eg 3.9 months [95%-CI=3.6-4.2] for NSCLC and 12.6 months [95%-CI=9.2-17.5] for urothelial carcinoma). NSCLC patients starting with medical therapy had OS between these limits. Median OS for NSCLC patients starting treatment with PD-L1/PD-1 ICIs was 21.4 months (95%-CI=13.9-not estimable).

Conclusion

Most patients with advanced NSCLC, urothelial carcinoma, epithelial ovarian cancer, gastric adenocarcinoma and RCC had poor OS in an era where only a minority received PD-L1/PD-1 ICIs. This information on treatment patterns and survival is important as a benchmarking real-world standard before widespread use of ICIs.

High-dose corticosteroid use and risk of hospitalization for infection in patients treated with immune checkpoint inhibitors--A nationwide register-based cohort study

High‐dose corticosteroids have been associated with increased risk of serious infection in patients with metastatic melanoma treated with immune checkpoint inhibitors targeting cytotoxic T‐lymphocyte antigen 4. This potential association needs to be examined further among patients with other cancer types and for other immune checkpoint inhibitors. We examined whether receipt of high‐dose corticosteroids was associated with increased rates of hospitalization for infection among 981 Danish renal, urothelial, and lung cancer patients followed from first administration of programmed death receptor 1 (PD‐1)/programmed death ligand 1 (PD‐L1) immune checkpoint inhibitors. Our cohort analysis was based on the information from national medical registries. During follow‐up, 522 patients (53.2%) initiated treatment with high‐dose corticosteroids and 317 patients (32.3%) experienced at least one hospitalization for infection. In analyses adjusted for age, sex, and previous use of chemotherapy/targeted therapy, initiation of high‐dose systemic corticosteroids was associated with increased rate of hospitalization for infections (hazard ratio (HR) = 2.96, 95% confidence interval (CI) = 2.41–3.65) even in patients not receiving any chemotherapy/targeted therapy (HR = 3.66, 95% CI = 2.25–5.96). Our findings showed that high‐dose corticosteroid initiation is associated with hospitalization for infection in patients treated with PD‐1/PD‐L1 immune checkpoint inhibitors. Clinicians and patients should be aware of this risk of infection when initiating treatment with high‐dose corticosteroids.

Revaccination with measles-mumps-rubella vaccine and hospitalization for infection in Denmark and Sweden - An interrupted time-series analysis

BACKGROUND

In a previous cohort study of 4-year-old Danish children, revaccination with the live measles-mumps-rubella vaccine (MMR) was associated with a 16% reduction in the rate of hospitalization lasting two days or longer for non-measles-mumps-rubella infections.

AIM

To examine if the introduction of revaccination with MMR at 4 years of age in Denmark (spring 2008) and at 7-9 years of age in Sweden (autumn 2009), at a time when there was virtually no measles, mumps or rubella cases, was associated with a reduction in the rate of hospitalization-for-infection lasting two days or longer at the population level.

METHODS

We included 4-year-olds in Denmark and 7-9-year-olds in Sweden. We obtained the number of hospitalization-for-infection lasting two days or longer from nationwide hospital registers. Person-years at risk were approximated from population statistics for each season and year. We performed an interrupted time series analysis using Poisson regression to estimate the change in hospitalization incidence rates following the introduction of MMR revaccination, adjusting for seasonality. We also performed analyses with control series (3-year-olds in Denmark and 4-year-olds in Sweden).

RESULTS

Comparing the incidence of hospitalization-for-infection lasting two days or longer after the introduction of MMR revaccination with the expected level without an introduction of MMR revaccination resulted in an incidence rate ratio of 1.07 (95% confidence interval [CI] = 0.89-1.28) for 4-year-olds in Denmark and 0.89 (95% CI = 0.77-1.02) for 7-9-year-olds in Sweden in analyses without controls. Analyses with controls gave similar results.

CONCLUSION

This population-level study of the introduction of MMR revaccination in Denmark and Sweden had inadequate power to confirm or refute the findings from an individual-level Danish study of an association between MMR revaccination and a lower incidence rate of hospitalization-for-infection lasting two days or longer.

Timeliness of DTaP-IPV-Hib Vaccination and Development of Atopic Dermatitis Between 4 Months and 1 Year of Age-Register-Based Cohort Study

BACKGROUND

An Australian study including 4433 children found that delayed Diphtheria-Tetanus-acellular Pertussis-containing vaccination was associated with reduced risk of developing atopic dermatitis (AD) before age 1 year.

OBJECTIVE

We assessed whether delayed vaccination against diphtheria, tetanus, acellular pertussis, polio, and Haemophilus influenzae type b (Diphtheria, Tetanus, acellular Pertussis - Inactivated Polio vaccine - Haemophilus influenzae type b [DTaP]) was associated with a reduced risk of new cases of AD before age 1 year in Denmark.

METHODS

We used nationwide registers to follow 883,160 children born in Denmark from 1997 to 2012. Binary regression models adjusting for potential confounding factors were applied to estimate relative risks (adjusted relative risks [aRRs]) of developing AD among children with delayed DTaP vaccination (defined as given 1 month or more after the recommended age) compared with timely vaccinated children.

RESULTS

Among 143,429 children with a delayed first dose of DTaP, 4,847 (3.4%) developed AD between age 4 months and 1 year, compared with 27,628 (3.7%) among 739,731 children not having delayed DTaP (aRR 0.94; 95% CI, 0.91-0.97). The aRR was 0.94 (95% CI, 0.90-0.99) for children with a delayed second dose, and the aRR was 0.88 (95% CI, 0.82-0.93) when comparing children with delayed first and second doses with all timely vaccinated children.

CONCLUSIONS

The results support the hypothesis that delayed vaccination with DTaP is associated with reduced risk of developing new cases of AD after age 4 months. The dose-dependent relationship strengthens the evidence of a causal relationship. Some countries are introducing maternal pertussis vaccination and delaying the first dose of DTaP, providing a possibility for further testing the hypothesis.

Measles, mumps and rubella vs diphtheria-tetanus-acellular-pertussis-inactivated-polio-Haemophilus influenzae type b as the most recent vaccine and risk of early 'childhood asthma'

BACKGROUND AND OBJECTIVE

Live vaccines may have beneficial non-specific effects. We tested whether the live measles, mumps and rubella (MMR) vaccine compared with the non-live diphtheria-tetanus-acellular-pertussis-inactivated-polio-Haemophilus influenzae type b (DTaP-IPV-Hib) vaccine as the most recent vaccine was associated with less childhood asthma and fewer acute hospital contacts for childhood asthma among boys and girls.

METHODS

This study is a nationwide register-based cohort study of 338 761 Danish children born between 1999 and 2006. We compared (i) the incidence of first-registered childhood asthma based on hospital contacts and drug prescriptions and (ii) the incidence of severe asthma defined as acute hospital contacts for childhood asthma between the ages of 15 and 48 months among children whose last received vaccine was three doses of DTaP-IPV-Hib and then MMR with children whose last received vaccine was three doses of DTaP-IPV-Hib.

RESULTS

For boys, following the recommended vaccine schedule of MMR after DTaP-IPV-Hib3 compared with DTaP-IPV-Hib3 as the last received vaccine, MMR was associated with 8.1 (95% confidence interval 3.9-12.3) fewer childhood asthma cases per 1000 boys, corresponding to 10% (5-15%) reduction in the cumulative incidence of childhood asthma. MMR, when given last, was also associated with 16.3 (95% confidence interval 12.7-20.0) fewer acute hospital admissions for childhood asthma per 1000 boys, corresponding to a 27% (22-31%) reduction in the cumulative incidence. No associations were seen for girls.

CONCLUSION

MMR may have a protective effect against childhood asthma for boys. This calls for an understanding of whether non-specific effects of vaccines can be used to optimize our vaccine programmes.

Vaccinology: time to change the paradigm?

The existing vaccine paradigm assumes that vaccines only protect against the target infection, that effective vaccines reduce mortality corresponding to the target infection's share of total mortality, and that the effects of vaccines are similar for males and females. However, epidemiological vaccine research has generated observations that contradict these assumptions and suggest that vaccines have important non-specific effects on overall health in populations. These include the observations that several live vaccines reduce the incidence of all-cause mortality in vaccinated compared with unvaccinated populations far more than can be explained by protection against the target infections, and that several non-live vaccines are associated with increased all-cause mortality in females. In this Personal View we describe current observations and contradictions and define six emerging principles that might explain them. First, that live vaccines enhance resistance towards unrelated infections. Second, non-live vaccines enhance the susceptibility of girls to unrelated infections. Third, the most recently administered vaccination has the strongest non-specific effects. Fourth, combinations of live and non-live vaccines given together have variable non-specific health effects. Fifth, vaccinating children with live vaccines in the presence of maternal immunity enhances beneficial non-specific effects and reduces mortality. Finally, vaccines might interact with other co-administered health interventions, for example vitamin A supplementation. The potential implications for child health are substantial. For example, if BCG vaccination was given to children at birth, if higher measles vaccination coverage could be obtained, if diphtheria, tetanus, and pertussis-containing vaccines were not given with or after measles vaccine, or if the BCG strain with the best non-specific effects could be used consistently, then child mortality could be considerably lower. Pursuing these emerging principles could improve our understanding and use of vaccines globally.

Phase-out of smallpox vaccination and the female/male HIV-1 prevalence ratio: an ecological study from Guinea-Bissau

OBJECTIVE

In Guinea-Bissau, West Africa, we observed that having a smallpox vaccination scar was associated with lower HIV-1 prevalence, more strongly for women than men. If this represents a causal effect, the female/male HIV-1 prevalence ratio would increase for birth cohorts no longer receiving smallpox vaccination due to the phase-out of this vaccine.

DESIGN

An ecological design using HIV surveys and information about smallpox vaccination coverage.

SETTING

Urban and rural Guinea-Bissau.

PARTICIPANTS

Participants in HIV surveys were grouped into an age group with decreasing smallpox vaccination coverage (15-34 years) and an age group with steady smallpox vaccination coverage (≥35 years).

INTERVENTIONS

The exposure of interest was the phase-out of the smallpox vaccine in Guinea-Bissau.

PRIMARY AND SECONDARY OUTCOME MEASURES

HIV-1 prevalence.

RESULTS

At both sites, the female/male HIV-1 prevalence ratio increased by calendar time for the age group with decreasing smallpox vaccination coverage; the combined female/male HIV-1 prevalence ratio among people aged 15-34 years was 1.00 (95% CI 0.17 to 5.99) in 1987-1990, 1.16 (95% CI 0.69 to 1.93) in 1996-1997, 2.32 (95% CI 1.51 to 3.56) in 2006-2007 (p value for no trend=0.04). There was no increase in the female-to-male HIV-1 prevalence ratio for the age group >35 years with steady smallpox vaccination coverage; 1.93 (95% CI 0.40 to 9.25) in 1987-1990, 1.32 (95% CI 0.83 to 2.10) in 1996-1997, 0.81 (95% CI 0.56 to 1.16) in 2006-2007 (p value for no trend=0.07).

CONCLUSIONS

Thus, data was compatible with the deduction that the phase-out of smallpox vaccination may have increased the susceptibility to HIV-1 relatively more for women than men. Hence, phasing out smallpox vaccination may have contributed to the global increase in the female/male HIV-1 prevalence ratio among young individuals. Due to the potential fallacies of ecological studies, the results should be interpreted carefully, and this hypothesis needs further assessment. If the hypothesis is true, studies of smallpox vaccination could inform HIV-1 vaccine research.

Hospitalizations for infections by age and sex: register-based study of Danish children 1977-2014

Background: Infectious diseases are a major cause of hospitalizations in children and there is increasing interest in sex differences in immunity during childhood. Therefore, we examined hospital admission rates for infectious diseases in Danish children by age and sex.Methods: Register-based cohort study of all Danish residents aged 0-14 years from 1977 to 2014. We examined total admission rate for infections and rates of admission by types of infection.Results: This study included 3,689,999 children and 1,080,750 admissions for infections. The admission rates peaked at age 0 months (boys, 197.9 admissions per 1000 person-years; girls, 160.9) and age 11 months (boys, 155.5; girls, 113.9). The male-female ratio of admissions was 1.25 for children aged 0-14 years, but varied by age and type of infection. Boys had the highest admission rate for any infection until 9 years of age after which girls had a higher rate. Boys had higher admission rates for gastrointestinal infections and lower respiratory tract infections than girls at all ages. The admission rates for upper respiratory tract infections and 'Other infections' for girls were higher than the rates for boys at age 10 and 4 years, respectively.Conclusions: Overall, boys had around 25% higher admission rates for infections than girls, with some variation according to age and type of infection.

Smallpox and BCG vaccination in childhood and cutaneous malignant melanoma in Danish adults followed from 18 to 49 years

BACKGROUND

Early smallpox and Bacillus Calmette-Guérin (BCG) vaccinations have been associated with reduced risk of cutaneous malignant melanoma (CMM). We assessed the association between pre-school smallpox vaccination and early-school BCG vaccination and CMM in a young Danish population.

METHODS

We conducted a register-based case-cohort study of individuals growing up during the phase-out period of smallpox and BCG vaccination in Denmark (born 1965-1976) utilising the decrease in vaccination during this period. Information on childhood vaccinations and potential confounders from Copenhagen school health records were linked with nationwide registers on cancer (CMM diagnoses), migrations and deaths by personal identification numbers.

RESULTS

The individuals were followed from age 18 until 31/12/2014 (maximum age at end of follow-up, 49 years). 188 cases of CMM occurred in the background population of 46,239 individuals; 172 CMM cases (91%) had full information and were analysed. The adjusted hazard ratio (HR) for CMM by BCG and/or smallpox vaccination compared with neither vaccine was 1.29 (95% confidence interval (CI) 0.72-2.31). For smallpox vaccination only, HR = 1.23 (95% CI 0.53-2.86) for BCG vaccination only, HR = 1.13 (95% CI 0.61-2.09) and for both smallpox and BCG vaccination, HR = 1.75 (95% CI 0.87-3.48) compared with none of these. Vaccination below the age of one year gave similar results.

CONCLUSIONS

We found no strong beneficial effect of smallpox and BCG vaccination against CMM among young adult Danes and with broad confidence intervals our data alone could be compatible with both modest preventive effects, no effects, and modest harmful effects. Our estimates do not contradict a potential modest beneficial effect of neonatal vaccination.

BCG Vaccination at Birth and Rate of Hospitalization for Infection Until 15 Months of Age in Danish Children: A Randomized Clinical Multicenter Trial

BACKGROUND

The bacillus Calmette-Guérin (BCG) vaccine against tuberculosis might reduce the non-tuberculosis-related child mortality rate in low-income settings. We tested the hypothesis that BCG vaccination at birth would reduce early childhood hospitalization for infection in Denmark, a high-income setting. Hospitalization for infection was a secondary outcome in a randomized trial with the primary aim to estimate the potential non-specific effects of BCG vaccination at birth on all-cause hospitalization.

METHODS

A total of 4262 children included in the Danish Calmette Study were assigned randomly to either receive the BCG vaccine or not and were followed through the Danish National Patient Register. The outcome was number of hospitalizations for infection until the age of 15 months. Data were analyzed by Cox regression in intention-to-treat (ITT) and per-protocol (PP) analyses.

RESULTS

In the ITT analysis, we observed 588 hospitalizations for infection (mean, 0.28 hospitalization per child) among the 2129 children allocated to receive the BCG vaccine and 595 hospitalizations for infection (mean, 0.28 hospitalization per child) among the 2133 children allocated to the control group (hazard ratio [HR], 0.99 [95% confidence interval (CI), 0.85-1.15]). The PP analysis yielded an HR of 1.00 (95% CI, 0.86-1.16).Predefined interaction ITT analyses showed that among 740 children with a BCG-vaccinated mother, the HR for BCG-vaccinated children was 0.65 (95% CI, 0.45-0.94); the HR for children who had a non-BCG-vaccinated mother was 1.10 (95% CI, 0.93-1.29) (P = .01, test of no interaction). Cesarean delivery modified the effect of BCG vaccination (HRs, 0.73 [95% CI, 0.54-0.99] in children born by cesarean section vs 1.10 [95% CI, 0.92-1.30] in other children; P = .02). When the outcome was defined as time to first hospitalization, the HR for premature children after BCG vaccination was 1.81 (95% CI, 0.95-3.43), whereas the HR was 0.94 (95% CI, 0.82-1.08) for children born at term (P = .05).

CONCLUSION

BCG vaccination did not affect the rate of hospitalization for infection up to the age of 15 months in Danish children. In future studies, the role of maternal BCG-vaccination, premature birth, and cesarean delivery needs further exploration.

How are children who are delayed in the Childhood Vaccination Programme vaccinated: A nationwide register-based cohort study of Danish children aged 15-24 months and semi-structured interviews with vaccination providers

Aims: Delay of childhood vaccinations is common and influences efforts to reduce targeted diseases. In Denmark, the diphtheria, tetanus, pertussis, polio and Haemophilus influenzae type b (DTaP-IPV-Hib) vaccine is recommended at ages 3, 5 and 12 months and the first measles-mumps-rubella vaccine (MMR-1) at 15 months. Following guidelines, children delayed at age 15 months should receive MMR-1 and DTaP-IPV-Hib-3 simultaneously, unless DTaP-IPV-Hib-2 was received less than 6 months ago, when MMR-1 alone is recommended. We studied compliance with these guidelines and the reasons for non-compliance with a focus on vaccination providers. Methods: We used a nationwide register-based cohort study of children born in Denmark between January 2000 and June 2013, who were lacking MMR-1 and DTaP-IPV-Hib-3 at age 15 months and were followed to 24 months. We also performed semi-structured telephone interviews with vaccination providers. Results: The study consisted of 156,921 children (18% of the children born in the period). Among the 40,060 children who had received DTaP-IPV-Hib-2 less than 6 months ago, 37,892 (95%) received MMR-1 alone. Among the 88,469 children who had received DTaP-IPV-Hib-2 more than 6 months ago, 6334 (7%) received DTaP-IPV-Hib-3 and MMR-1 simultaneously. The interviews indicated that some vaccination providers are reluctant to give multiple vaccinations at the same visit and some have a preference of following the usual sequence in the programme. Conclusions: Vaccination providers generally complied with the recommended minimum 6 months' interval between DTaP-IPV-Hib-2 and DTaP-IPV-Hib-3. Conversely, there was a low compliance with the recommendation to administer DTaP-IPV-Hib-3 and MMR-1 simultaneously. More efforts are needed to ensure timely vaccination.

Vaccinations against smallpox and tuberculosis are associated with better long-term survival: a Danish case-cohort study 1971-2010

Background: When vaccinations with vaccinia against smallpox and Bacillus Calmette-Guérin (BCG) against tuberculosis were phased out in some high-income countries around 1980, the impact on overall mortality was not examined. Recent studies from low-income countries have suggested that these vaccines are associated with mortality reductions, not explained by specific disease protection. We examined whether vaccinia and BCG administered in childhood were associated with long-term mortality reductions in a high-income population.

Methods: In this case-cohort study, we followed 47 622 schoolchildren from Copenhagen, Denmark, born 1965 to 1976, from their first health examination to 2010. This cohort experienced the phase-out of vaccinia and BCG vaccination programmes.

Results: A sub-cohort of 5 316 individuals (699 excluded) was followed for 164 450 person-years (0.2% were lost to follow-up), and 401 deaths due to natural causes (841 deaths in total) occurred in the full cohort. Compared with individuals who had not received vaccinia or BCG, those who had received both vaccinia and BCG had an adjusted hazard ratio (aHR) of 0.54 [95% confidence interval (CI): 0.36–0.81] for mortality due to natural causes of death; those who only received BCG had an aHR of 0.58 (95% CI: 0.39–0.85). Vaccinia and BCG were not associated with any protection against deaths by accidents, suicide or murder, the combined aHR being 0.94 (95% CI: 0.62–1.42).

Conclusions: Vaccinia and BCG vaccinations were associated with better long-term survival, which was not explained by specific protection. Vaccines with beneficial non-specific effects may reduce overall mortality even after the target diseases are eradicated.

The Effect of Smallpox and Bacillus Calmette-Guérin Vaccination on the Risk of Human Immunodeficiency Virus-1 Infection in Guinea-Bissau and Denmark

Background

The live smallpox and Bacillus Calmette-Guérin (BCG) vaccinations have been associated with better adult survival in both Guinea-Bissau and Denmark. In Guinea-Bissau, human immunodeficiency virus (HIV)-1 became an important cause of death after smallpox vaccination was phased out globally in 1980. We hypothesised that smallpox and BCG vaccinations were associated with a lower prevalence of HIV-1 infection, and we tested this hypothesis in both Guinea-Bissau and Denmark.

Methods

We conducted 2 studies: (1) a cross-sectional study of HIV infection and vaccination scars in Guinea-Bissau including 1751 individuals and (2) a case-base study with a background population of 46239 individuals in Denmark. In Guinea-Bissau, HIV-1 transmission was almost exclusively sexually transmitted. In Denmark, we excluded intravenous drug users. Data were analyzed using logistic regression.

Results

Bacillus Calmette-Guérin and/or smallpox vaccination compared with neither of these vaccines was associated with an adjusted odds ratio (aOR) for HIV-1 of 0.62 (95% confidence interval [CI], 0.36–1.07) in Guinea-Bissau and 0.70 (95% CI, 0.43–1.15) in Denmark. We combined the results from both settings in a meta-analysis (aOR = 0.66; 95% CI, 0.46–0.96). Data from Guinea-Bissau indicated a stronger effect of multiple smallpox vaccination scars (aOR = 0.27; 95% CI, 0.10–0.75) as follows: women, aOR = 0.18 (95% CI, 0.05–0.64); men, aOR = 0.52 (95% CI, 0.12–2.33); sex-differential effect, P = .29.

Conclusions

The studies from Guinea-Bissau and Denmark, 2 very different settings, both suggest that the BCG and smallpox vaccines could be associated with a decreased risk of sexually transmitted HIV-1. It might be informative to pursue this observation and explore possible protective mechanisms as part of the search for an HIV-1 vaccine.

BCG vaccination at birth and early childhood hospitalisation: a randomised clinical multicentre trial

BACKGROUND

The BCG vaccine is administered to protect against tuberculosis, but studies suggest there may also be non-specific beneficial effects upon the infant immune system, reducing early non-targeted infections and atopic diseases. The present randomised trial tested the hypothesis that BCG vaccination at birth would reduce early childhood hospitalisation in Denmark, a high-income setting.

METHODS

Pregnant women planning to give birth at three Danish hospitals were invited to participate. After parental consent, newborn children were allocated to BCG or no intervention within 7 days of age. Randomisation was stratified by prematurity. The primary study outcome was number of all-cause hospitalisations analysed as repeated events. Hospitalisations were identified using The Danish National Patient Register. Data were analysed by Cox proportional hazards models in intention-to-treat and per-protocol analyses.

RESULTS

4184 pregnant women were randomised and their 4262 children allocated to BCG or no intervention. There was no difference in risk of hospitalisation up to 15 months of age; 2129 children randomised to BCG experienced 1047 hospitalisations with a mean of 0.49 hospitalisation per child compared with 1003 hospitalisations among 2133 control children (mean 0.47), resulting in a HR comparing BCG versus no BCG of 1.05 (95% CI 0.93 to 1.18) (intention-to-treat analysis). The effect of BCG was the same in children born at term (1.05 (0.92 to 1.18)) and prematurely (1.07 (0.63 to 1.81), p=0.94). The effect was also similar in the two sexes and across study sites. The results were essentially identical in the per-protocol analysis and after adjustment for baseline characteristics.

CONCLUSIONS

BCG vaccination at birth did not reduce the risk of hospitalisation for somatic acquired disease until 15 months of age in this Danish study population.

TRIAL REGISTRATION NUMBER

NCT01694108, results.

Simultaneous vaccination with MMR and DTaP-IPV-Hib and rate of hospital admissions with any infections: A nationwide register based cohort study

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Nationwide retrospective cohort study of Danish children aged 15 months to 4 years.

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Comparison of the live MMR + the inactivated DTaP-IPV-Hib vaccine vs MMR alone.

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27% higher rate of admissions for lower respiratory infections for MMR + DTaP-IPV-Hib.

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No significant association with admissions for other types of infections.

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Adjustment for a long range of potential confounders including exact age.

Background

In Denmark, live measles, mumps, and rubella vaccine (MMR) is associated with a reduced risk of infectious disease admissions, particularly for lower respiratory tract infections. In low-income countries, simultaneous vaccination (i.e. vaccination at the same visit) with live and inactivated vaccines may increase child mortality compared with the live vaccine alone. We examined the hypothesis that simultaneous administration of MMR and the inactivated DTaP-IPV-Hib vaccine compared with MMR alone is associated with higher incidence of infectious disease admissions.

Methods

Nationwide, retrospective, register based cohort study of 520,859 children born in Denmark 1997–2006, who were followed from 15 months to 4 years of age. Incidence rate ratios (IRRs) of hospital admissions were estimated by Cox regression and adjusted for background factors including exact age.

Results

By 2 years of age, 4965 children had simultaneous MMR and DTaP-IPV-Hib as their most recent vaccination. Compared with MMR alone, simultaneous administration was associated with a higher rate of lower respiratory tract infections (adjusted incidence rate ratio (IRR), 1.27; 95% confidence interval (CI), 1.13–1.42). There was no effect on other infections. Overall, simultaneous administration was associated with a 7% (95% CI, 0–15%) increase in infectious disease admissions.

Conclusions

Simultaneous administration of MMR and DTaP-IPV-Hib compared with MMR alone may increase the rate of hospital admissions related to lower respiratory tract infections. These findings require replication in other high-income settings.

A marginal structural model for recurrent events in the presence of time-dependent confounding: non-specific effects of vaccines on child hospitalisations

Using a Danish register-based study on childhood vaccination and hospitalisation as motivation, a marginal structural model for recurrent events is studied. The model addresses a number of challenges which may be seen more generally in large register-based cohort studies. One is to adjust for a time-dependent confounder when studying the effect of a time-varying exposure on a recurrent event based on an analysis in continuous time. Another is to report results via a measure which is easy to interpret and communicate even though quite elaborate treatment regimes are considered. Lastly, the implementation of continuously updated weights implies a substantial computationally demanding workload. Copyright © 2016 John Wiley & Sons, Ltd.

Oral Polio Vaccination and Hospital Admissions With Non-Polio Infections in Denmark: Nationwide Retrospective Cohort Study

In a nationwide Danish register-based cohort study, the live oral polio vaccine was associated with fewer admissions for lower respiratory infections compared with the inactivated DTaP-IPV-Hib vaccine. There was no difference between oral polio vaccine and measles-mumps-rubella vaccine.

Background. Live vaccines may have nonspecific beneficial effects on morbidity and mortality. This study examines whether children who had the live-attenuated oral polio vaccine (OPV) as the most recent vaccine had a different rate of admissions for infectious diseases than children with inactivated diphtheria-tetanus-pertussis-polio-Haemophilus influenzae type b vaccine (DTaP-IPV-Hib) or live measles-mumps-rubella vaccine (MMR) as their most recent vaccine.

Methods. A nationwide, register-based, retrospective cohort study of 137 403 Danish children born 1997–1999, who had received 3 doses of DTaP-IPV-Hib, were observed from 24 months (first OPV dose) to 36 months of age.

Results. Oral polio vaccine was associated with a lower rate of admissions with any type of non-polio infection compared with DTaP-IPV-Hib as most recent vaccine (adjusted incidence rate ratio [IRR], 0.85; 95% confidence interval [CI], .77–.95). The association was separately significant for admissions with lower respiratory infections (adjusted IRR, 0.73; 95% CI, .61–.87). The admission rates did not differ for OPV versus MMR.

Conclusions. Like MMR, OPV was associated with fewer admissions for lower respiratory infections than having DTaP-IPV-Hib as the most recent vaccination. Because OPV is now being phased-out globally, further studies of the potential beneficial nonspecific effects of OPV are warranted.

Live vaccine against measles, mumps, and rubella and the risk of hospital admissions for nontargeted infections

IMPORTANCE

In low-income countries, live measles vaccine reduces mortality from causes other than measles infection. Such nonspecific effects of vaccines might also be important for the health of children in high-income settings.

OBJECTIVE

To examine whether the live vaccine against measles, mumps, and rubella (MMR) is associated with lower rates of hospital admissions for infections among children in Denmark.

DESIGN, SETTING, AND PARTICIPANTS

Population-based cohort study of Danish children born 1997-2006 and followed up from ages 11 months to 2 years (last follow-up, August 31, 2008). Nationwide Danish registers provided data on vaccinations and hospital admissions. The recommended vaccination schedule was inactivated vaccine against diphtheria, tetanus, pertussis, polio, and Haemophilus influenzae type b (DTaP-IPV-Hib) administered at ages 3, 5, and 12 months and MMR at age 15 months.

MAIN OUTCOMES AND MEASURES

Incidence rate ratios (IRRs) of hospital admissions for any infection, comparing receipt of MMR vs DTaP-IPV-Hib as the most recent vaccine. Risks, risk difference, and number needed to vaccinate were calculated for receiving MMR on time.

RESULTS

The study included 495,987 children contributing with 56,889 hospital admissions for any type of infection during 509,427 person-years (rate, 11.2 per 100 person-years). For the 456,043 children who followed the recommended schedule and received MMR after the third dose of DTaP-IPV-Hib, MMR (rate, 8.9 per 100 person-years) vs the third dose of DTaP-IPV-Hib (rate, 12.4 per 100 person-years) as the most recent vaccine was associated with an adjusted IRR of 0.86 (95% CI, 0.84-0.88) for any admission for infection. There were 19,219 children immunized out of sequence. The adjusted IRR was 0.87 (95% CI, 0.80-0.95) for those receiving MMR (rate, 9.9 per 100 person-years) after the second dose of DTaP-IPV-Hib (rate, 15.1 per 100 person-years). However, in the 1981 children who subsequently received the third dose of DTaP-IPV-Hib (rate, 12.8 per 100 person-years) after MMR, the IRR for hospital admissions for infection was significantly greater (adjusted IRR, 1.62 [95% CI, 1.28-2.05]). The risk of admission for an infection between ages 16 months and 24 months was 4.6% (95% CI, 4.5%-4.7%) for receiving MMR on time and 5.1% (95% CI, 5.0%-5.2%) for not receiving MMR on time. The risk difference was 0.5 percentage point (95% CI, 0.4-0.6), and the number needed to vaccinate with MMR before age 16 months to prevent 1 admission for any infection was 201 (95% CI, 159-272).

CONCLUSIONS AND RELEVANCE

In a cohort of Danish children, receipt of live MMR vs inactivated DTaP-IPV-Hib as the most recent vaccine was associated with a lower rate of hospital admissions for any infections. These findings require replication in other high-income populations.

Smallpox vaccination and all-cause infectious disease hospitalization: a Danish register-based cohort study

BACKGROUND

There is growing evidence from observational studies and randomized trials in low-income countries that vaccinations have non-specific effects. Administration of live vaccines reduces overall child morbidity and mortality, presumably due to protection against non-targeted infections. In Denmark, the live vaccine against smallpox was phased out in the 1970s due to the eradication of smallpox. We used the phasing-out period to investigate the effect of smallpox vaccination on the risk of hospitalization for infections.

METHODS

From the Copenhagen School Health Records Register, a cohort of 4048 individuals was sampled, of whom 3559 had information about receiving or not receiving smallpox vaccination. Infectious disease hospitalizations were identified in the Danish National Patient Register.

RESULTS

During 87,228 person-years of follow-up, 1440 infectious disease hospitalizations occurred. Smallpox-vaccinated individuals had a reduced risk of all-cause infectious disease hospitalization compared with smallpox-unvaccinated individuals [hazard ratio (HR) 0.84; 95% confidence interval (CI) 0.72-0.98]. The reduced risk of hospitalizations was seen for most subgroups of infectious diseases. The effect may have been most pronounced after early smallpox vaccination (vaccination age <3.5 years: HR 0.81; 95% CI 0.69-0.95; vaccination age ≥ 3.5 years: HR 0.91 95% CI 0.76-1.10). Among the smallpox-vaccinated, the risk of infectious disease hospitalization increased 6% with each 1-year increase in vaccination age (HR 1.06; 95% CI 1.02-1.10).

CONCLUSION

Smallpox vaccination is associated with a reduced risk of infectious disease hospitalization in a high-income setting.

Risk of lymphoma and leukaemia after bacille Calmette-Guérin and smallpox vaccination: a Danish case-cohort study

Vaccines may have non-specific effects as suggested mainly in mortality studies from low-income countries. The objective was to examine the effects of BCG and smallpox vaccinations on subsequent risk of lymphoma and leukaemia in a Danish population experiencing rapid out-phasing of these vaccines. In a background cohort (N=47,622) from the Copenhagen School Health Records Register, cases of leukaemia (N=20) and lymphoma (N=51) were identified through the Danish Cancer Registry. The vaccination status of the cases was compared with the vaccination status of a 5% random sample (N=2073) of the background cohort and analysed in a case-cohort design. BCG vaccination reduced the risk of lymphomas (HR=0.49 (95% CI: 0.26-0.93)), whereas smallpox vaccination did not (HR=1.32 (0.56-3.08)). With the small number of leukaemia cases, the analysis of leukaemia had limited power (BCG vaccination HR=0.81 (0.31-2.16); smallpox vaccination HR=1.32 (0.49-3.53)). The present study with very reliable vaccine history information indicates a beneficial effect of BCG vaccination on the risk of lymphomas.

Child care is not a substantial risk factor for gastrointestinal infection hospitalization

OBJECTIVE

The objective was to study the effect of age at first enrollment into child care and other child care-related factors on the risk for hospitalization from gastrointestinal infection.

METHODS

This was a population-based prospective cohort study of 1,110,973 Danish children aged 0 to 5 years in the period 1989-2004. By means of Poisson regression, risk for gastrointestinal infection hospitalization was evaluated by incidence rate ratio and 95% confidence intervals.

RESULTS

Overall, children who were attending child care had an IRR of gastrointestinal infection hospitalization of 1.02 compared with children in home care. When compared within the group of children who attended child care, those who were enrolled after 18 months of age had a slightly increased risk compared with those who were enrolled before 1 year of age. The first 5 months of enrollment were associated with an IRR of 1.18 compared with later periods, and similar risks were observed in different types of child care facilities. The effect of child care was similar in most strata of the studied child, family, and demographic variables; however, children younger than 1 year who attended child care had an IRR of 1.44 compared with children of the same age in home care. Well established risk factors for gastrointestinal infection such as young age and male gender were reproduced; compared with 5-year-olds, children younger than 1 year had an IRR of 7.37 and boys had an IRR of 1.18 compared with girls.

CONCLUSIONS

The results of this study suggest that child care attendance is not a substantial risk factor for gastrointestinal infection hospitalization in most Danish children. Late enrollment and the first short period of enrollment were associated with a slightly increased risk for gastrointestinal infection hospitalization.