Childhood vaccinations and risk of acute lymphoblastic leukaemia in children

Vaccination Coverage during Childhood and Adolescence among Undergraduate Health Science Students in Greece

High rates of vaccination coverage in childhood represent one of the most important cost-effective tools of primary prevention and have substantially reduced the incidence of and mortality from vaccine-preventable diseases globally. Vaccination coverage of young people has not been well estimated in Greece. Anonymous self-completed questionnaires and the participants’ Child Health Booklet were used to estimate complete vaccination coverage of mandatory vaccinations against vaccine-preventable diseases of undergraduate students at the University of West Attica during the academic year 2020−2021. Student’s t-tests were used to estimate mean values. Overall, 79% (95% CI: 78−81%) of study participants were fully vaccinated. This coverage was lower in males especially for vaccines that should be done during childhood (p = 0.045). High vaccination percentage (>90%) was observed for the meningococcus group A, C, W135, Y, measles-mumps-rubella, hepatitis B and meningitis C vaccine. Nevertheless, suboptimal coverage was assessed for the booster dose of tetanus, diphtheria, pertussis, for the human papillomavirus vaccine among girls, for the tuberculosis, for the meningococcus group B, for the pneumococcal, and for the seasonal influenza vaccines. In conclusion, the promotion of routine vaccination programs for young adults needs to be strengthened. An identification system for under-vaccinated students, an efficient reminder system and university campus vaccine program practices should be established, particularly among males.

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.