Can children with minor illnesses be safely immunized?

Health care providers often have difficulty convincing parents that it is acceptable to administer vaccines such as measles, mumps and rubella (MMR), and combined diphtheria, tetanus, acellular pertussis, inactivated poliomyelitis, Haemophilus type b conjugate (DTaP/IPV/Hib) to an infant who is mildly ill. Providers may not be confident about this recommendation. What is the evidence that minor illnesses are not a contraindication to most vaccinations? The Canadian Immunization Guide (1) and the Advisory Committee on Immunization Practices (2) recommend that minor illnesses, such as a mild upper-respiratory infection with or without low-grade fever, not be considered as contraindications to routine vaccination. There are two considerations: Is the practice safe? Can it impair responses to the vaccine(s)? The live, attenuated viral vaccines could, in theory, be affected by active, nonspecific, antiviral responses in the child, resulting in interferon production. This is mainly localized to areas of inflammation such as the upper airways of children with a cold. This consideration does not apply to systemically administered vaccines such as MMR. Four large, prospective, cohort studies from Canada and the United States compared MMR vaccination in children with mild illness and healthy controls, and found no effect of mild illness on the antibody response to any of the vaccine components (3–5) or to either the measles or the rubella component (6). These studies included a total of 1338 children between 12 and 23 months of age; 723 had mild illnesses (including 669 with upper respiratory infection, 41 with otitis media and 13 with diarrhea) and 615 were healthy controls. Additionally, a population-based case series and case-control study that compared 170 children with measles and 6070 control children (7) found that MMR vaccination during the respiratory virus season did not increase the risk of vaccine failure. No association was evident between mild illness and rates and severity of adverse events after MMR vaccination (8). Most fevers or seizures associated with MMR occur a week or more after the vaccination, thereby affording most children with an uncomplicated viral infection time to recover. Delaying vaccination for moderate or severe acute illness with or without fever is recommended for MMR vaccination (1,2,8) to avoid real or imagined interaction of symptoms. For live vaccines administered as a nasal spray, such as FluMist (MedImmune, USA), minor illnesses with or without fever are not a contraindication. However, colds with nasal congestion might limit delivery of the vaccine to the nasal lining and, thus, are considered to be a reason to delay vaccine administration (9). What about inactivated childhood vaccines? They are less susceptible to immune interference but cause more immediate adverse effects, peaking soon after vaccination. No publication in recent decades has assessed administering inactivated vaccines to mildly sick children. Safety data from clinical trials of modern DTaP/IPV/Hib vaccines given concurrently with pneumococcal conjugate vaccine indicate fever rates of up to 25% (10), mainly during the evening after vaccination. Adding this potential fever to a pre-existing fever is a practical concern, recognizing the fear that moderate or high fever elicits in many parents (11). Deferring vaccination may be prudent for the febrile child, but this is unnecessary for children with minor illnesses without fever, when inactivated vaccines are indicated. In summary, the health care provider should be reassured that mild illness is not a reason to delay routine vaccination. Many good-quality studies have provided strong support for the recommendation. Deferring vaccinations for common, minor ailments in children has been shown to result in missed opportunities for vaccination, so it should be limited to selected febrile children. The Upshots column in Paediatrics & Child Health is meant to address practical questions without ready answers in standard references such as the Red Book or the Canadian Immunization Guide. Readers are invited to submit questions to the Journal office. A timely response will be provided, whenever possible, from one member of a panel of experts. The most interesting exchanges will be selected for publication. Submitters should identify themselves, but will be given the option of anonymity in the published version. Submit questions directly to journal@cps.ca. Please note that these may be edited for clarity and brevity. David Scheifele MD Associate Editor, Paediatrics & Child Health

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