What are the contraindications to vaccination?

Vaccination contraindications refer to specific medical circumstances in which administering a vaccine is not recommended due to an increased risk of adverse effects or lack of expected benefit. These are broadly categorized as either “absolute” (where vaccination should be deferred or avoided entirely) or “relative” (where the risks and benefits must be carefully weighed on an individual basis).

An absolute contraindication includes a documented history of a severe allergic reaction—specifically anaphylaxis—occurring within minutes after a prior dose of the same vaccine or to a known component (e.g., gelatin, egg protein in certain influenza vaccines, or polyethylene glycol [PEG] in some mRNA-based COVID-19 vaccines). Another absolute contraindication is the presence of a confirmed, current, moderate-to-severe acute illness with fever; in such cases, vaccination is typically postponed until the patient has recovered, to avoid attributing nonspecific symptoms (e.g., fever, malaise) to the vaccine rather than the underlying illness.

Relative contraindications include immunocompromised states—such as those resulting from hematologic malignancies, solid organ or hematopoietic stem cell transplantation, or high-dose corticosteroid therapy—for live attenuated vaccines (e.g., varicella, MMR, yellow fever), which carry a theoretical risk of uncontrolled replication. Pregnancy is also considered a relative contraindication for live vaccines, although inactivated, recombinant, subunit, polysaccharide, and mRNA vaccines are generally safe and routinely recommended during pregnancy when indicated.

It is important to emphasize that many commonly cited concerns—such as mild illness without fever, stable chronic conditions (e.g., controlled asthma, diabetes, or epilepsy), previous non-anaphylactic reactions (e.g., hives alone), or a family history of adverse events—are not valid contraindications. In fact, individuals with chronic illnesses often derive greater benefit from vaccination due to their heightened risk of vaccine-preventable disease complications. Clinical judgment, thorough patient history, and up-to-date guidance from authoritative sources (e.g., CDC, WHO, or national immunization technical advisory groups) are essential in determining appropriate vaccination strategies.