Herd Susceptibility: A New Mass Tort?

Posted By Chris Laliberté

“I noticed that her fingers and her mind were not working together and she couldn’t do anything.
‘Are you feeling all right?’ I asked her. ‘I feel all sleepy,’ she said.
In an hour, she was unconscious.
In twelve hours she was dead.”
–Roald Dahl

I am ten years old. Ashley, the babysitter, wakes me up, serves me breakfast, and walks me to the end of the snow-laden, car-free driveway. My bus driver, Mary-Ann, greets me with a knowing smile, but the downward curve in the wrinkles at the corners of her eyes betrays the concern behind her cheer. Mary-Ann loved every kid who rode that bus like her own grandchild, and one of us had taken ill.

While I run around at recess, snooze through long division, and blast my way through StarFox, my parents spend every night in the hospital with my younger brother, Jonah. My parents wring their hands and pace beside Jonah’s hospital bed as every day, his tiny seven year-old body grapples with scarlet fever. Thankfully, with the help of the team at Hôtel Dieu Hospital, my brother survives.

Jonah was the same age then as Roald Dahl’s daughter, Olivia, when measles encephalitis stole the light from her eyes, and from her father’s life. Neither Dahl nor my parents had a proven and effective vaccine available to protect their child against such terrifying diseases; both, having witnessed the devastation wrought upon their beloved children, would have accepted such help without question.

To know a loved one, especially a child, is at the mercy of a deadly pathogen—a force over which medical professionals have only limited control after infection—induces the worst kind of fear, the fear that this intrusion on your loved one’s health could cause them permanent harm. That the risks adopted by another parent could introduce such a threat to a vulnerable child poses more than an ethical dilemma—I propose that the endangerment of others through the disruption of herd immunity raises a possible cause for legal action in the doctrine of negligence.

Herd Immunity & the Duty to Vaccinate

In large part, vaccines owe the success of their inoculative effects to the herd immunity principle. Contagions require viable hosts for the infection to spread; in a vaccinated community the immunized population creates a barrier that protects those who, for health reasons, cannot receive vaccinations themselves.

The success of herd immunity depends on immunizing the greatest possible proportion of the population. While most can accept vaccines without issue, a small percentage of people cannot due to various health-related reasons, including pregnancy, allergies, or compromised immune systems. Every person able but unwilling to accept vaccinations therefore increases the risk of exposure for this vulnerable minority. In effect, this risk implies a moral duty to vaccinate.

A Legal Right to Refuse Treatment…

The issue proves more complex when trying to establish a legal duty. All persons in Canada retain a right to refuse medical treatment. This right is entrenched in arts. 10-18 CCQ in Quebec, and under legislation such as s.10(1) of Ontario’s Health Care Consent Act in the Common Law provinces. To force anyone to accept vaccinations would violate this right to bodily integrity.

Further, since opting out of vaccinations poses no substantial or immediate risk to the child’s well-being, it seems unlikely that Courts would deprive parents of their authority over their child’s medical care, a right confirmed in B(R) v Children’s Aid Society of Metropolitan Toronto. Under ordinary circumstances, s. 7 of the Charter protects a right to personal autonomy, including a parent’s “right to choose medical treatment for their infants.” A Court would therefore likely not force a parent to have their child vaccinated.

The entrenchment of and need to protect these rights causes me to question both the ethics and the effects of bringing criminal negligence charges against parents who refuse to vaccinate their child, as some have suggested. Assuming an identifiable party at fault for an outbreak, innocent families who have suffered could find a more reasonable and, arguably, effective recourse in civil action.

…and a Legal Wrong to Cause Harm

While many might consider this refusal an omission, I would consider the exercise of any right, even one of refusal, an action. The importance of this distinction lies in the need to first establish a duty to act before an omission constitutes negligence. This step does not exist in claims based on actions, as actions carry the “legal duty to refrain from conduct that a reasonable person would know […] might constitute an unreasonable risk of harm to others.” It is therefore much simpler to sue on an action rather than an omission since the right to act in a certain way does not protect against the risks incurred by the action.

Harvard Law professor Arthur L. Caplan and his co-writers recently laid out a roadmap for success in a hypothetical civil suit, and the same criteria could satisfy the Canadian test for negligence. Caplan argues that, in the case of a rare disease like the measles, “epidemiological analysis could link the two children with a high degree of confidence” to provide a reliable case for causation.

With causation established, a civil action grounded in the tort of negligence relies on proof of a failure to take reasonable precautions by the party at fault. A failure to account for the foreseeable possibility of an unvaccinated child contracting measles and exposing peers to the disease could prove a breach of duty of care, and strengthen the case for prima facie tortious negligence.

In terms of damages, plaintiffs could make arguments for pain and suffering as well as the quantifiable medical costs incurred.


Parents who exercise their right to refuse vaccinations for their child retain the right to do so pursuant to legislation that protects the integrity of the person and allows patients to refuse medical treatment. The exercise of this right, however, should not release parents who refuse to vaccinate from the duty to take reasonable care to protect herd immunity and the health of those who lack the option to vaccinate. A failure to take these reasonable precautions could cement a prima facie claim of tortious negligence against the parents at fault.

Both the moral and legal situations surrounding the right to refuse vaccinations prove as clear to some as they are nebulous to others. No reasonable person, however, can ignore the fact that measles, whooping cough, and other formerly scarce diseases continue to mount a resurgence in direct correlation with the lowest vaccination rates in decades. We have forgotten the threat these diseases pose, the reason we sought their eradication. As more tragedies like the recent Disneyland outbreak unfold, I hope more parents will remember Roald Dahl’s plea after the death of his daughter:

“It is not yet generally accepted that measles can be a dangerous illness.
Believe me, it is. In my opinion parents who now refuse to vaccinate
their children are putting the lives of those children at risk. […]
It really is almost a crime to allow your child to go unimmunized.”

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