Vaccination during febrile illness, what do we know? A systematic-narrative hybrid review of the literature and international recommendations

Introduction

Vaccination during febrile illness (FI) is often regarded as a contraindication, leading to its postponement in most cases. Considering the doubts about the immunogenicity, efficacy and safety of the procedure among physicians and patients, we sought in this review to assess the data in the literature and international recommendations in terms of vaccination during FI.

Methods

This review was conducted according to the methodological structure for systematic-narrative hybrid reviews, using PubMed and Cochrane library databases until March 2024. Inclusion criteria were studies dealing with vaccination during FI in children or adults, and exclusion criteria were studies related to post-vaccination fever or animal experiments. A review of international recommendations was also carried out. Articles included were fully examined by the authors for eligibility.

Results

Our literature search enabled us to identify six studies about the immunogenicity and safety of vaccination during FI in children. All have shown no significant differences in seroconversion rates, protective antibody levels or adverse events between children vaccinated during FI and controls. Nine articles on physicians and patients' attitudes regarding immunization during FI were also included in this review. Vaccination was frequently postponed in cases of fever, primarily to avoid potential complications. Review of international recommendations allowed us to classify countries into three categories: those recommending vaccination regardless of the body temperature, those recommending vaccination within a temperature limit, and those with unclear recommendations.

Discussion

The immunogenicity and safety studies were only conducted in children, yet results were reassuring. Despite using the same evidence, recommendations differed from country to another. This situation may explain the reluctance of physicians and patients to embrace this practice. Postponing vaccination is however associated with low vaccine coverage and could be considered a missed opportunity to vaccinate. A higher level of evidence seems needed for a firm conclusion.