Is there a must avoid vaccine?

The short version: no vaccine is a universal "must avoid," but several have clear contraindications for specific people, and the evidence for those is thin in the wrong places.

The question is about individual contraindications, not population-level risk. The evidence here covers a few specific scenarios. For people with a known anaphylaxis to a vaccine component like polyethylene glycol (PEG), the mRNA COVID-19 vaccines are contraindicated. A 2021 case report documents a healthcare worker who had an allergic reaction to PEG in the Pfizer-BioNTech vaccine [1], and a 2022 case report describes a 35-year-old woman who developed Brighton level 1 anaphylaxis immediately after her second dose [4]. The UK's MHRA initially issued a broad contraindication for people with a history of anaphylaxis to any vaccine, but a 2021 commentary argued that was overly restrictive [3]. The evidence is clear: if you have a confirmed allergy to a specific ingredient, that vaccine is a must-avoid for you.

For people with egg allergy, the picture is more nuanced. A 2025 review concluded that most vaccines with egg-derived components are safe, but yellow fever vaccine carries a 1.29% risk of anaphylactic shock in people with egg hypersensitivity [6]. The same review found that influenza vaccine in egg-allergic people has a reported risk of allergic reaction of 0.001% [6]. A 2015 study of 282 atopic children with egg allergy found that live attenuated influenza vaccine (LAIV) was well tolerated with no systemic allergic reactions [11]. So for egg allergy, the yellow fever vaccine is a must-avoid unless alternatives exist, but influenza and MMR vaccines are not.

For people with mastocytosis, a 2023 review found that prophylactic vaccination is generally safe, with adverse reactions comparable to or only slightly higher than the general population [5]. In one study of 634 vaccine doses given to mastocytosis patients, 4 adverse reactions occurred, all after hexavalent vaccine, and the most common reaction was generalized urticaria [5]. An NIH retrospective study of 94 children with mastocytosis found that 89.4% had no severe or moderately severe adverse reactions, but one child had anaphylaxis following chickenpox vaccine [5]. So mastocytosis is not a blanket contraindication, but the chickenpox vaccine may warrant caution.

For people with a history of immune thrombocytopenic purpura (ITP), the MMR vaccine is a known trigger. A 1994 case report describes exacerbation of chronic ITP following MMR vaccination [18], and a 2010 systematic review found that MMR-associated ITP is rare but documented, with incidence rates ranging from 0.087 to 4 per 100,000 doses depending on the country [19]. The evidence is clear: MMR is a must-avoid for someone with active or recent ITP.

The evidence here is thin in critical ways. Most of it comes from case reports and small observational studies, not large randomized trials with hard clinical endpoints. The safety data for egg-allergic people receiving influenza vaccine comes from a single review that cites a 0.001% risk figure [6], but the original studies behind that number are not provided. The mastocytosis data is from a narrative review that explicitly notes "there are no large and controlled studies in this patient group" [5]. The ITP data is from a systematic review, but the incidence rates vary wildly by country (from 0.087 to 4 per 100,000), which suggests the true rate is poorly measured [19].

My call: for a person with a confirmed allergy to a vaccine component, that vaccine is a must-avoid. For egg allergy, avoid yellow fever but not influenza or MMR. For mastocytosis, no vaccine is a must-avoid, but chickenpox warrants caution. For active ITP, avoid MMR. For everyone else, the evidence here does not identify a must-avoid vaccine, but that is not the same as proof of safety. Confidence: moderate for the specific contraindications listed, low for the general safety of any vaccine in any person.