Immunizations against infectious diseases and childhood cancers

Vaccination and the Risk of Childhood Cancer-A Systematic Review and Meta-Analysis

INTRODUCTION

Infections may play a role in the etiology of childhood cancer and immunizations may be protective because vaccinations stimulate the immune system. Observational studies reported inconsistent associations between vaccination and risk of childhood cancer. Since a synthesis of the evidence is lacking, we conducted a meta-analysis stratified by histological and site-specific cancer.

METHODS

We performed a systematic review (CRD42020148579) following PRISMA guidelines and searched for literature in MEDLINE, Embase, and the Science Citation Index databases. We identified in three literature databases 7,594 different articles of which 35 met the inclusion criteria allowing for 27 analyses of 11 cancer outcomes after exposure to nine different types of vaccinations. We calculated summary odds ratios (ORs) and 95% confidence intervals (CIs) using random effects models.

RESULTS

We observed four inverse associations between childhood leukemia and certain vaccines as well as the number of vaccinations: OR 0.49 (95% CI = 0.32 to 0.74) for leukemia death after bacillus Calmette-Guérin vaccination; OR 0.76 (95% CI = 0.65 to 0.90) for acute lymphoblastic leukemia after Haemophilus influenzae type b vaccination; OR 0.57 (95% CI = 0.36 to 0.88) for leukemia; and OR 0.62 (95% CI = 0.46 to 0.85) for acute lymphoblastic leukemia after three or more vaccinations of any type. All other conducted analyses did not show any associations.

DISCUSSION

The results are consistent with the hypothesis that vaccinations reduce the risk of childhood leukemia. However, the robustness and validity of these results is limited due to the small number, substantial heterogeneity, and methodological limitations of available studies.

Infectious Agents in Childhood Leukemia

Acute leukemia is the most common pediatric cancer, representing one-third of all cancers that occurs in under 15 year olds, with a varied incidence worldwide. Although a number of advances have increased the knowledge of leukemia pathophysiology, its etiology remains less well understood. The role of infectious agents, such as viruses, bacteria, or parasites, in the pathogenesis of leukemia has been discussed. To date, several cellular mechanisms involving infectious agents have been proposed to cause leukemia following infections. However, although leukemia can be triggered by contact with such agents, they can also be beneficial in developing immune stimulation and protection despite the risk of leukemic clones. In this review, we analyze the proposed hypotheses concerning how infectious agents may play a role in the origin and development of leukemia, as well as in a possible mechanism of protection following infections. We review reported clinical observations associated with vaccination or breastfeeding, that support hypotheses such as early life exposure and the resulting early immune stimulation that lead to protection.

Associations between vaccination and childhood cancers in Texas regions

OBJECTIVES

To determine whether children born in Texas regions with higher vaccination coverage had reduced risk of childhood cancer.

STUDY DESIGN

The Texas Cancer Registry identified 2800 cases diagnosed from 1995 to 2006 who were (1) born in Texas and (2) diagnosed at ages 2 to 17 years. The state birth certificate data were used to identify 11 200 age- and sex-matched control subjects. A multilevel mixed-effects regression model compared vaccination rates among cases and control subjects at the public health region and county level.

RESULTS

Children born in counties with higher hepatitis B vaccine coverage had lower odds of all cancers combined (OR = 0.81, 95% CI: 0.67 to 0.98) and acute lymphoblastic leukemia (ALL) specifically (OR = 0.63, 95% CI: 0.46 to 0.88). A decreased odds for ALL also was associated at the county level with higher rates of the inactivated poliovirus vaccine (OR = 0.67, 95% CI: 0.49 to 0.92) and 4-3-1-3-3 vaccination series (OR = 0.62, 95% CI: 0.44 to 0.87). Children born in public health regions with higher coverage levels of the Haemophilus influenzae type b-conjugate vaccine had lower odds of ALL (OR: 0.58; 95% CI: 0.42 to 0.82).

CONCLUSIONS

Some common childhood vaccines appear to be protective against ALL at the population level.

Vaccination history and risk of childhood leukaemia

BACKGROUND

Previous studies on vaccination and childhood leukaemia generated inconsistent results.

METHODS

In the Northern California Childhood Leukaemia Study, a case-control study with incident cases and matched birth certificate controls, detailed written vaccination records were collected. A total of 323 cases aged 0-14 years at diagnosis and 409 controls were included in this analysis. All vaccinations were censored on the reference date (date of diagnosis for cases and the corresponding date for matched controls). Conditional logistic regression analysis was conducted, adjusting for potential confounding factors. A primary variable of interest is the number of administrations (doses) of various types of vaccines.

RESULTS

Vaccinations against diphtheria, pertussis, tetanus, poliomyelitis, measles, mumps, and rubella were not associated with the risk of leukaemia. The odds ratio for each dose of Haemophilus influenzae type b (Hib) vaccine was 0.81 (95% CI 0.68-0.96). Compared with children who received two or fewer doses of Hib vaccine, those who received three or more doses had a significantly reduced risk of childhood leukaemia (odds ratio = 0.55, 95% confidence interval 0.32-0.94). The number of doses of hepatitis B vaccine received was not associated with leukaemia risk.

CONCLUSIONS

Hib vaccination is associated with a reduced risk of childhood leukaemia. Future studies with detailed exposure assessment and large sample sizes are needed to further address the role of vaccinations in the etiology of childhood leukaemia.

Haemophilus influenzae type B vaccination and risk of childhood leukaemia in a vaccine trial in Finland

Incidence of childhood leukaemia was studied among subjects of a trial comparing administration of several doses of a conjugate vaccine against Haemophilus influenzae type b (Hib) starting at an early age (three months) with a single dose given at the age of two years. Among 114 000 subjects, a total of 77 cases of childhood leukaemia were detected. The incidence of childhood leukaemia was lower in the early vaccination arm (relative risk 0.72, 95% confidence interval 0.46-1.13) than late vaccination arm, but the difference did not reach statistical significance. Our results suggest that early immunization against Hib may reduce the incidence of childhood leukaemia, but confirmatory studies are needed.

The United Kingdom Childhood Cancer Study: objectives, materials and methods. UK Childhood Cancer Study Investigators

An investigation into the possible causes of childhood cancer has been carried out throughout England, Scotland and Wales over the period 1991-1998. All children known to be suffering from one or other type of the disease over periods of 4-5 years have been included, and control children matched for sex, age and area of residence have been selected at random from population registers. Information about both groups of children (with and without cancer) has been obtained from parental questionnaires, general practitioners' and hospital records, and from measurement of the extent of exposure to radon gas, terrestrial gamma radiation, and electric and magnetic fields. Samples of blood have also been obtained from the affected children and their parents and stored. Altogether 3,838 children with cancer, including 1,736 with leukaemia, and 7,629 unaffected children have been studied. Detailed accounts are given of the nature of the information obtained in sections describing the general methodology of the study, the measurement of exposure to ionizing and non-ionizing radiation, the classification of solid tumours and leukaemias, and the biological material available for genetic analysis.

Infant vaccinations and risk of childhood acute lymphoblastic leukaemia in the USA

Previous studies have suggested that infant vaccinations may reduce the risk of subsequent childhood leukaemia. Vaccination histories were compared in 439 children (ages 0-14) diagnosed with acute lymphoblastic leukaemia (ALL) in nine Midwestern and Mid-Atlantic states (USA) between 1 January 1989 and 30 June 1993 and 439 controls selected by random-digit dialing and individually matched to cases on age, race and telephone exchange. Among matched pairs, similar proportions of cases and controls had received at least one dose of oral poliovirus (98%), diphtheria-tetanus-pertussis (97%), and measles-mumps-rubella (90%) vaccines. Only 47% of cases and 53% of controls had received any Haemophilus influenzae type b (Hib) vaccine (relative risk (RR) = 0.73; 95% confidence interval (CI) 0.50-1.06). Although similar proportions of cases (12%) and controls (11%) received the polysaccharide Hib vaccine (RR = 1.13; 95% CI 0.64-1.98), more controls (41%) than cases (35%) received the conjugate Hib vaccine (RR = 0.57; 95% CI 0.36-0.89). Although we found no relationship between most infant vaccinations and subsequent risk of childhood ALL, our findings suggest that infants receiving the conjugate Hib vaccine may be at reduced risk of subsequent childhood acute lymphoblastic leukemia. Further studies are needed to confirm this association and, if confirmed, to elucidate the underlying mechanism.

Association of childhood leukaemia with factors related to the immune system

The childhood peak of common acute lymphoblastic leukaemia has been proposed as being a rare response to delayed exposure to a common infection. In this context, factors related to the child's immune system are of special interest. Information on such factors was obtained in a recent German case-control study comprising more than 1000 children with acute leukaemia. Neither being the first-born child, nor a short duration of breastfeeding, indicators of a deficit in viral contacts during infancy or the number of infectious diseases, were significant risk factors. We observed a strong association with fewer routine immunizations with a 3.2-fold increase for those children getting less than four immunizations, but this association could partly be explained by reporting bias. While tonsillectomy or appendectomy increased the risk of leukaemia in our studies, a protective effect of allergies could be seen. In summary, we found only weak support for the delayed exposure hypothesis. To some extent this may be due to the chosen surrogate markers which reflect, rather indirectly, immunological isolation in infancy and delayed exposure to common viruses. However, the significant findings for routine immunizations, tonsillectomy and allergies of the child or its parents merit further investigation.

The risk profile of childhood leukaemia in Greece: a nationwide case-control study

The risk profile of childhood leukaemia in Greece was studied through a case-control investigation that included all 153 incident cases of the disease, ascertained throughout the country during 1993 and 1994, and two hospital controls for every case matched for gender, age and place of residence. The data were analysed using conditional logistic regression and the associations are expressed in terms of adjusted odds ratios (OR) and their 95% confidence intervals. Cases were born to mothers of a higher standard education, the OR for an increment of four schooling years being 1.48 (1.17-1.87) and had higher birth weight, the OR for an increment of 500g being 1.36 (1.04-1.77). Pet ownership and birth after a pregnancy with anaemia were associated with increased risk, the ORs being 2.18 (1.14-4.16) and 2.60 (1.39-4.86) respectively. From the frequency analyses, indicative inverse associations were found with birth order, household crowding and previous hospitalization with allergic diseases, whereas indicative positive associations were found with diabetes mellitus during pregnancy and with neonatal jaundice. Substantial or significant elevations were not found with respect to maternal smoking and coffee drinking during pregnancy, diagnostic radiography and ultrasonographic examinations or blood transfusions. A significant inverse association with maternal consumption of alcohol could be due to multiple comparisons, but a detrimental effect can probably be excluded. A non-significant positive association with total shots of viral vaccinations and a weak non-significant inverse association with breast feeding were also found. We interpret the findings of this study as being compatible with acute childhood leukaemia being linked with delayed development of herd immunity to fairly common infectious agents, in conjunction with accelerated perinatal and early post-natal growth.

Childhood cancers and competing causes of death

From the survey that first identified cancer effects of foetal irradiation and related sources has come support for the following hypotheses: (1) competing causes of death for childhood cancers include abortions (solid tumours) and infections (RES neoplasms); (2) the forms taken by RES neoplasms vary with the nature and intensity of indigenous infections; (3) ideal conditions for developing diffuse RES neoplasms (leukaemia) include the gross immunological incompetence caused by trisomy 21; (4) the unusually localised RES neoplasms found in children who have survived repeated attacks of malaria (Burkitt lymphoma and chloroma) are probably the result of these children having exceptionally high levels of passive as well as active immunity; and (5) when teratogenic effects of in utero mutations include faulty erythropoiesis as well as faulty leucopoiesis, infections are not the only rival causes of death.

Viruses, clusters and clustering of childhood leukaemia: a new perspective?

Clusters of childhood leukaemia have, during a lengthy and controversial history, focussed attention on two alternative putative aetiological agents: infections and localised environmental pollution. In the United Kingdom emphasis is currently placed on the latter because of reports of localised clusters in the vicinity of two nuclear reprocessing plants. Now the most recent studies of spatial clustering in the United Kingdom also support the hypothesis that a substantial population of cases of childhood acute lymphoblastic leukaemia (ALL) arise as a rare host response to certain patterns of exposure to common infectious agents--the aberrant response model. Relevant aspects of the epidemiology of ALL are reviewed from this perspective and the hypothesis shown to be capable of unifying reported associations with different types of risk factor. It is probable that specific agent(s) are involved though none have been identified and these may share many epidemiological characteristics of herpes viruses. The possible relevance of these results to associations with prenatal parental occupational exposures to dusts and ionising radiation is explored.

The inter-regional epidemiological study of childhood cancer (IRESCC): case-control study of children with central nervous system tumours

Tumours of the central nervous system comprise 23% of all childhood cancers and form the most common group of solid malignancies. Little is know about their aetiology. The present report concerns the results of a case-control study of 78 incident cases of central nervous system tumours in children. No case-control differences were detected for the following: pre-natal diagnostic X-rays, general anaesthetics during pregnancy, pregnancy infections, pregnancy drugs (including sedatives, tranquillizers and anti-convulsants), alcohol consumption in pregnancy, child's birthweight, breast-feeding, childhood illnesses, previous medication in the child. A significant excess of case mothers had suffered from diseases of the nervous system (RR 2.6). There was a deficit of children who had been immunised among the case children which approached significance, and an excess of congenital abnormalities among cases which also approached significance. There was a small excess of neoplastic disease among case parents. The results of this study suggest that in our patients genetic rather than environmental factors are more important, but the small numbers included in the present study meant that no definite conclusions could be reached.

A case-control study of non-T cell acute lymphoblastic leukaemia of children in Hokkaido, Japan

STUDY OBJECTIVE

The purpose of the study was to investigate factors associated with the occurrence of childhood acute lymphoblastic leukaemia in cases identified as of non-T cell type, stage I-IV.

DESIGN

The study was a case-control investigation. Data were obtained by interview with parents of cases and controls.

SETTING

The study was community based and was carried out in Hokkaido, Japan.

SUBJECTS

63 cases were identified. Controls (two for each case) were matched for sex, age and place of residence.

MEASUREMENTS AND MAIN RESULTS

In univariate analysis, BCG vaccination, measles infection, measles vaccination, atopy, hip x ray, and milk intake of mother during pregnancy had significantly low odds ratios (ie, were less likely to be associated with leukaemia), while dental x rays for carious teeth and contact with animals at time of diagnosis had high odds ratios (more likely to be associated with leukaemia). In conditional logistic regression analysis employing these seven factors, measles infection/vaccination, BCG, atopy and dental x ray remained significant.

CONCLUSIONS

Leukaemia subtypes are likely to have specific aetiologies. Future epidemiological research in leukaemia should take this into account.

The Inter-Regional Epidemiological Study of Childhood Cancer (IRESCC): past medical history in children with cancer

The Inter-Regional Epidemiological Study of Childhood Cancer (IRESCC) collected interview and medical information relating to the child's past medical experiences from parents of 555 children diagnosed with cancer and parents of 1110 unaffected matched controls. No significant associations emerged overall for ante-natal care, place and mode of delivery, length of gestation, birth weight, condition at birth, special care, neonatal procedures or breast-feeding. Few risk factors relating to previous illnesses and medication were found, although increasing numbers of illnesses appeared to be associated with an increased risk of childhood cancer, particularly acute lymphoblastic leukaemia. A highly significant excess of case children had not been immunised (p = 0.005). In general, these results indicate that past medical experiences have little influence on the development of cancer in children.

The inter-regional epidemiological study of childhood cancer (IRESCC): a case control study of aetiological factors in leukaemia and lymphoma

The inter-regional epidemiological study of childhood cancer analysed data on 234 children diagnosed with leukaemia or lymphoma and 468 controls matched for age and sex. A wide range of potential risk factors was examined, including prenatal exposure to x rays, maternal drug ingestion and smoking, child's medical history, and parental medical conditions and occupation. Calculations were completed for leukaemia or lymphoma and diagnostic subgroups, as defined by laboratory confirmed cell type. In utero exposure to narcotic analgesics was weakly associated with leukaemia or lymphoma but no other antenatal factors gave significant risks. New associations were identified for skin diseases in both parents and congenital abnormalities in the mothers of children with leukaemia. For past medical conditions in the child, viral disease occurring under 6 months of age increased the risk for acute lymphoblastic leukaemia. Fewer children in the leukaemia or lymphoma group had been immunised compared with the control groups. Case children diagnosed over the age of 9 years were more likely than controls to have had four or more previous episodes of illness. Overall, these results indicate that prenatal factors may be less important than postnatal or genetic influences in the development of leukaemia or lymphoma in children.