CPHA Canvax

Immunization stress-related responses: Improving our understanding of a type of adverse event following vaccination

C. Meghan McMurtry - PhD, C.Psych, Associate Professor of Psychology, University of Guelph.

G. is a 15-year-old girl waiting in line to get her immunization at school. She starts to feel a bit dizzy and her heart starts to pound. G. becomes worried about what the needle is going to feel like. By the time she reaches the nurse, all she wants to do is get out of there. She faints immediately after the needle is removed.

The problem: Needles can be stressful for some individuals, and ignoring this does not make it go away.

Vaccines protect the public from a number of diseases and are a clear public health success story. Immunizations are typically delivered through injections; the process has a number of characteristics that can increase distress: pain from the injection, fear, sight of a needle, sight of blood, prolonged standing, and responses by others in the environment (1). Youth are particularly at risk of distress, as immunizations are common throughout childhood. Pain and fear can go hand in hand: the more fearful an individual is about a needle, the more pain that individual will report experiencing (1). Most people who have high levels of needle fear report a previous negative experience (1). If we do not understand and manage negative experiences associated with immunizations, public confidence in vaccines can be compromised.

Consequences of high needle fear

Safety monitoring and “anxiety”: We need a better way to understand what is going on. 

The safety of vaccinations is monitored globally. Adverse events following immunization (AEFI) are grouped into 5 different categories, including events that are seen as arising from “anxiety” about immunization (2). More recently, we have recognized that calling these “anxiety” reactions is problematic:

Anxiety reactions

How do Immunization stress-related responses present?

Other AEFIs can occur only after immunization ‒ but ISRR can occur immediately before, during, or after.


Before, during, or immediately after immunization (<5 minutes)

Acute stress response: “fight-flight-freeze” response. Manifestations range depending on severity, and could include “butterflies in the tummy” and low to moderate levels of worry; more severe responses could include difficulty breathing or rapid breathing/hyperventilation and increased heart rate.

Vasovagal response: fainting-type response, ranging from feeling mildly dizzy to actually losing consciousness due to insufficient blood flow to the brain.

An acute stress response may be followed by a vasovagal reaction following a sudden decrease in heart rate and blood pressure.


After immunization

Dissociative neurological symptom response: neurological symptoms without any identified physical findings. These symptoms could include difficulty walking, moving a limb, weakness, tingling, and non-epileptic seizures. These have not been well documented/reported in individuals following immunization, but there are reports of “mass” reactions or “clusters” of these reactions in multiple people in close proximity.

Image - Pencil

The acute stress response, vasovagal response, and dissociative neurological symptom response in individuals or in groups of individuals (known as “clusters”) can occur and has occurred without any relationship to immunization. In other words, these responses can occur in individuals or clusters and have nothing to do with immunization, and in other cases, they may be reported after immunization.

There is a detailed causality process used by the World Health Organization (WHO) to determine whether there is any relation between the symptoms and immunization; more details can be found in the ISRR manual (3). ISRR is not caused by the vaccine product, vaccine quality defects, or an immunization program error.


How can we understand immunization stress-related responses?

Each person to be immunized comes to the immunization process with their own history, psychological strengths and vulnerabilities, and perceptions of the procedure and social context. Experiencing an ISRR is not the person’s fault. The diagram below illustrates ISRR in individual and group contexts (3). Notes to understand the diagram:

  • Three broad time points: before the immunization (historical, predisposing factors), in the immunization context (precipitating factors, initial response), and after the immunization (delayed response influenced by perpetuating factors).
  • Risk factors: shapes with a patterned fill show examples of potential risk factors for experiencing an ISRR; gears show the dynamic interactions among risk factors.
  • Progression: the person being immunized is shown at different times with examples of risk factors leading to a cascade of symptoms (initial response, ongoing) consistent with ISRR; however, not everyone will progress from one stage to another, step by step. For example, there is no requirement that a dissociative neurological symptom reaction must follow an acute stress response.
  • Social media’s potential to provide negative information is highlighted.

Immunization stress-related responses

So why should we care? Understanding immunization stress-related responses can facilitate prevention and appropriate early intervention.

ISRR and other AEFIs require different prevention approaches and treatment responses. For example, it is important to distinguish ISRR from anaphylaxis, which is life-threatening and requires urgent recognition and a particular pharmacologic response (IM epinephrine) and expert management. ISRR is not life-threatening, would not be helped by epinephrine, and requires different management.

How can I help? What else do I need to know? How do I find this information?

A full exploration of how to prevent, manage, and report ISRR is beyond the scope of this CANVax In Brief. A detailed manual for healthcare professionals is in its final stages at the WHO (3). The manual contains clear detailed guidelines on:

  • Screening and Prevention: The healthcare team should be calm, confident, and friendly, and communicate well with the recipient and any caregivers to build trust. People at high risk for ISRR should be identified by screening for high levels of needle fear and previous negative experiences with needles, including fainting. Additional measures need to be put in place for these individuals (e.g., vaccinating in private, lying down, plus muscle tension technique for fainting). Pain management strategies should be used (4). Advance planning for mass immunization contexts is important.
  • Differentiating anaphylaxis and seizures from ISRR.
  • Intervention:
    • For ISRR in the context of the immunization: stay calm. Rule out other potential reactions (e.g., anaphylaxis). It may resolve spontaneously. Keep the person safe from injury. Avoid medication and hospitalization.
    • For ISRR occurring after the immunization context: treatment will depend on the symptoms but will likely include a multidisciplinary approach with clinicians with specific expertise. The aim will be to increase functioning.
  • Reporting the ISRR as part of AEFI surveillance.
  • Specific considerations for a mass or cluster ISRR (e.g., school-based vaccination programs). Social factors will be critical to understand here.

A synopsis of the detailed manual and a manuscript in a peer-reviewed journal are also forthcoming.


1. McMurtry CM, Pillai Riddell R, Taddio A, Racine N, Asmundson GJG, Noel M, Chambers CT, Shah V, HELPinKids&Adults Team. Far from “just a poke”: common painful needle procedures and the development of needle fear. Clin J Pain 2015.

2. Council for International Organizations of Medical Sciences (2012). Definition and application of terms for vaccine pharmacovigilance: Report of CIOMS/WHO Working Group on vaccine pharmacovigilance. https://www.who.int/vaccine_safety/initiative/tools/CIOMS_report_WG_vaccine.pdf

3. Immunization stress-related response: A manual for program managers and health professionals to prevent, identify and respond to stress-related responses following immunization. Content developed by: Gold M, McDonald N, McMurtry CM, Pless, R, Heininger, U. Produced under coordination and supervision of MR Balakrishnan and P Zuber and supported by L Menning and O Benes from WHO.

4. Taddio A, McMurtry CM, Shah V, et al. Reducing pain during vaccine injections: clinical practice guideline. CMAJ 2015. DOI:10.1503 /cmaj.150391 http://www.cmaj.ca/content/187/13/975