Can individuals infected with COVID-19 sue those who unintentionally transmitted the novel coronavirus to them? This article explores the effectiveness of using the tort of negligence as a legal tool to reduce the spread of COVID-19.1 In particular, there exists a wide duty of care upon each individual towards another’s physical well-being not to transmit the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) – the cause of the highly infectious COVID-19 disease that transpired into a global pandemic.2 Considerations for the reasonableness of departing from the orthodox approach on duty of care derived from other commutable diseases are informed by the novel features of COVID-19, and possible perverse incentives not to seek early testing if the duty of care not to transmit COVID-19 is defined too narrowly. Having established this duty of care, the argument then considers using a proportionality test to assess the standard of care, balancing individual autonomy against public health considerations, the value of which would be to limit this tortious liability in practice. Lastly, this article further explores the potential difficulties in proving causation and proposes to adopt the Bonnington test based on material contribution to cumulative physical injuries. Notwithstanding the paucity of case law related to COVID-19, this article conducts a comparative analysis with the current literature related to the transmission of other types of viral diseases, particularly the deadly Human Immunodeficiency Virus (HIV). In the meantime, it shall be noted from the outset that discussion related to the possible use of strict liability regime or intentional torts to control the spread of COVID-19 (which could even become subjects of criminal prosecution) are beyond the scope of this article.
Duty of Care
The rationale underlying the duty not to negligently transmit COVID-19 shall first be assessed under the common law’s two models of tort, namely the Model of Wrongs and the Model of Costs. Under the Model of Wrongs3, corollary to an individual’s right to physical health is another’s duty to respect the other person’s state of natural health. Such a duty gives rise to a standard of conduct in relation to COVID-19 transmission (discussed later in this article), to which failure to comply results a wrong being committed. In justifying this duty, Ripstein’s conception of mutual independence4, and thus the duty not to take charge of others’ means, would see a duty incumbent upon each individual not to conduct him/herself in a way that negligently transmits COVID-19 to the harm of another’s body.
In comparison, Calabresi’s Model of Costs5 would seek to allocate the duty not to negligently transmit COVID-19 upon the party “best placed” to decide on the most efficient way of minimising costs related to COVID-19 transmission. Here, a potentially COVID-19-infectious individual is arguably the “best decider” of his or her own risk of COVID-19 transmission and the associated costs of taking precaution against such transmission. Indeed, a caveat is attached to the word “arguably” because the state might be the “better decider” than potentially COVID-19-infectious individuals, if, for example, a majority of the population unduly under-estimates the severity of COVID-19. This might furnish sufficient grounds for the state to intervene by introducing relevant regulations to manage COVID-19 transmissions.6.= Nevertheless, a legislative debate is beyond the purview of this article; and for present purpose, it is sufficient to see potentially COVID-19-infectious individuals being at least the “better decider” vis-à-vis COVID-19 victims, thus placing on the former the duty not to negligently transmit COVID-19 under a liability regime. In this respect, both the Model of Wrongs and the Model of Costs could be used to understand the duty not to negligently transmit COVID-19, albeit from different perspectives.
In fact, the Calabresi “best-decider” Model of Costs also sheds light on who should potentially become amendable to the duty not to negligently transmit COVID-19. Understandably, a potentially COVID-19-infectious individual has better knowledge of his or her own social interaction history than COVID-19 victims. This superior knowledge thus puts a potentially COVID-19-infectious individual in a better position vis-à-vis a COVID-19 victim to decide how COVID-19 transmission from him/herself should best be reduced. This reasoning not only forms the basis of the duty not to negligently transmit COVID-19, but also explains established duties of care not to negligently transmit other types of commutable diseases. This is in line with other common law jurisdictions (particularly US jurisdictions) that have engaged the issue of disease transmission using tort liability regimes. For example, in Hendricks v. Butcher7, the Missouri Court of Appeal established a duty of care for those with smallpox virus not to spread their infection; in Berner v. Caldwell8, the Supreme Court of Alabama also imposed a duty on individuals infected with herpes to protect his or her sexual partners from infection. Nevertheless, the different symptoms and modes of transmission of smallpox, herpes, and COVID-19 could mean that the scope of tort liability would be different for each disease. The characteristic skin sores on smallpox patients9, and the transmission of herpes through sexual activities10, imply that those who do not demonstrate the relevant smallpox symptoms, or those who do not engage in the relevant sexual activities, would not need to bear any duties as the “best decider” – because there exist no costs to minimise in the first place. In contrast, the air-borne capability of SARS-CoV-211 and the asymptomatic spread of COVID-1912 could make everyone potentially infectious. As the UK Coronavirus Act 2020, Schedule 21 Part 1 Section 2(1) aptly provides: a person is “potentially infectious” at any time if:
a) the person is, or may be, infected or contaminated with coronavirus, and there is a risk that the person might infect or contaminate others with coronavirus, or
b) the person has been in an infected area within the 14 days preceding that time.13
At the time of this writing, COVID-19 has spread across 213 countries and territories across the globe.14 It is therefore safe to say that any travellers entering the UK would qualify as “potentially infectious” by virtue of Section 2(1)(b) for being within an area reported to have coronavirus within the preceding 14 days. However, it is also worth noting that Section 2(1) only refers to countries, territories, and areas outside the UK.15 Nevertheless, given that the UK itself ranks the 14th globally for the greatest number of COVID-19 cases at the time of this writing16, the territories that shall be deemed as “potentially infectious”, for the normative purpose of this article, shall be understood to also include the UK.
Arguably, such a wide duty of care might seem to undermine the principle of minimum intervention and individual autonomy. However, defining the scope of tort liability surrounding COVID-19 based on the traditional jurisprudence of other types of viral diseases would be guilty of ignoring the novel features of COVID-19 discussed above. In addition, there also exist public policy grounds that would make a wide-ranging duty not to negligently transmit COVID-19 compatible with the “fair, just, reasonable” requirement of the Caparo test.17 At the time of this writing, testing facilities for COVID-19 are still not readily accessible in many parts of the world18, and suspected patients cannot get their test results immediately after taking the diagnostic test.19 This potential double delay in both getting a test and getting the result of a test, coupled with the highly commutable nature of SARS-CoV-2,20 would result in considerable virus leak within the community between the time the suspected patient seeks to access a test and the time the patient is confirmed as a positive case of COVID-19. Such virus leak and the consequent build-up of yet-to-confirm COVID-19 patients would result in further delay in receiving test results, if the testing capacity of the locality did not expand at a rate commensurate with the infection rate. This consequently sets up a vicious cycle in which further virus leak is perpetuated within the larger community.
Additionally, if the duty of care not to transmit COVID-19 is only limited to those individuals who received positive results from their COVID-19 tests, this would, on the contrary, create perverse incentives for people not to seek testing at an early stage. If individuals fear that they may have COVID-19 and the test results transpired to be positive, they can readily face liability in negligence if the virus was indeed transmitted to others. Instead, the claimants would not be able to establish a duty to act if people do not take COVID-19 tests and are therefore ignorant of their diseases. Although the doctrine of wilful blindness21 may capture those defendants who deliberately close their minds to further inquiries in fear of validating their suspicion, this doctrine is nonetheless only effective in exceptional cases when the possibility of being COVID-19-positive is obvious. However, asymptomatic spread is what has made COVID-19 so hard to control, thus making early-stage testing and speedy diagnosis even more important than for other types of viral diseases. Undoubtedly, such perverse incentive would be dangerous from a public health perspective. If potentially infectious individuals are unaware that they are carriers of SARS-CoV-2, they might unknowingly transmit the virus to others through subsequent social encounters, spreading the virus exponentially to the greater community.
Therefore, in view of the novel features of COVID-19 and the above analysis on the dire public health consequences on limiting the duty of care only to confirmed COVID-19 patients, there is indeed a case to depart from the conventional duty of care established in the jurisprudence of other commutable diseases. Considerations for the extent of the negligence liability related to COVID-19 transmission would be assessed through careful calibration of the standard of care, which would be discussed below.
Standard of Care
According to Bolton v. Stone22, a defendant is not negligent if the risk of foreseeable damage is small and the cost of taking precaution is disproportionately high. In the context of COVID-19, this involves balancing the reasonably perceived risk of transmitting COVID-19 against the cost of taking preventive measures to reduce the spread of COVID-19. Various preventive measures could attract different degrees of cost on an individual’s autonomy, ranging from comparatively small inconvenience such as social distancing for a certain radius, or wearing a mask, goggles, or a face shield, to comparatively greater limitation on one’s movement such as self-isolation or quarantine. Similarly, for corporate entities, there is also a spectrum of costs related to taking various preventive measures, ranging from the provision of sanitising and protective equipment, enhanced cleaning regimes, and reduced business capacity for social-distancing measures, to ultimate shut-down of business. What specific preventive measures that each individual (or corporate entity) has to take – and consequently what degrees of cost that each individual (or corporate entity) has to bear – in discharge of their duty of care would depend on a reasonable perception of both the consequences and the risks of COVID-19 transmission in individual circumstances. In this regard, in assessing how much individual autonomy should be compromised, this article proposes a proportionality test in determining the standard of care, balancing the cost of taking preventive measures against both the consequences and the risk of transmitting COVID-19 to others.
However, in applying this proportionality test, even in the jurisprudence of other commutable diseases, there is no clear line regarding how substantial a risk must be before the defendant’s conduct constitutes negligence. In the case of HIV infections (decided in the tort law context), in Mussivand v. David23, the Ohio Supreme Court held that “a person who knows, or should know, that he or she is infected with a venereal disease has the duty to abstain from sexual conduct or, at a minimum, to warn those persons with whom he or she expects to have sexual relations of his or her condition”. In Doe v. Roe24, the New York Court of Appeal stated that the use of a condom may even shield defendants from negligence liability. Similarly, the Law Commission of England and Wales25 even considered whether disclosure of disease status is still required when the risk of STD transmission is low, either because the infected person used a condom, or was undergoing antiretroviral treatment. All these have shown that even infected individuals may nonetheless be deemed to have exercised an acceptable level of care without having to refrain from sexual activities. Despite the differences between STD and COVID-19 discussed in the previous section, both viral diseases are at least commutable among humans and preventive measures including wearing a condom (in the case of STD) and wearing a mask (in the case of COVID-19) are preventive measures aimed to significantly reduce, though not to eradicate, transmission. This is in line with the Learned Hand test26 under the Model of Costs (and indeed the reasoning behind Bolton v. Stone 27 which requires precautions to be taken only if the statistical multiple of the probability and the consequence of harm is cost-effective. Both sexual activities (in the case of STD transmission) and social interactions (in the case of COVID-19 transmission) are fundamentally desirable activities that the law does not discourage – but only if carried out in a cost-efficient way. Therefore, in the context of COVID-19, a potentially infectious individual may not necessarily have to go to the extent of undergoing self-isolation to discharge the duty of care not to transmit COVID-19 – mask-wearing is likely to be sufficient in ordinary circumstances. Having said so, it must be noted that Calabresi’s Model of Costs28 also requires individuals to consider the consequences of transmission.29 Specifically, in view of the higher risk of severe COVID-19 for older adults30 and people with underlying health conditions31, potentially infectious individuals need to exercise greater care than simply wearing masks in order to discharge their duty of care. Ignorance of these special circumstances, where greater care is required to prevent COVID-19 transmission to individuals at increased risks, is unlikely to succeed as a defence, in view of the wide-spread media coverage of COVID-19 and its related specialty risks.
In the meantime, it is also impossible to ignore the strength of the counterargument based on individual autonomy, which finds its support in the jurisprudence of other types of viral diseases. In the context of STD, both Weait32 and Cherkassky 33 have argued that everyone has a responsibility to minimise the transmission of STD and people who do not ask their partners whether or not they are infected should be responsible for failing to protect their own health. With due respect, this argument still does not attenuate the defendants’ liability for engaging in acts that they knew to be potentially harmful and indeed had harmed others.34 In fact, allowance has already been made to defendants’ autonomy by allowing consent to be used as a justificatory defence. In this regard, informed consent by the victim should be seen as the ultimate acknowledgement that defendants had done what they could reasonably be expected to do in the circumstances to protect victims from potential harm. Having said so, applying the doctrine of informed consent to COVID-19 would produce bizarre and economically costly results in everyday interactions. For one thing, a person who is aware or suspects that she is a carrier of COVID-19 would need to seek everyone’s consent before she could board the Tube. This is clearly not viable in practice.
As an alternative to informed consent, the operation of implied consent35 presumes that riders of public transport have consented to the risk of contracting COVID-19 when they boarded the crowded Tube – either because they perceive the consequence of infection as not serious enough or the risk of infection as an obvious and acceptable fact. Therefore, wearing a mask is seemingly not a matter of fulfilling one’s duty of care not to transmit COVID-19 to others, but rather a measure of self-protection adopted by individuals who do not wish to be taken as impliedly consented to the risk of contracting COVID-19 when moving around in public. A corollary of this argument is that any preventive measures mentioned in this section shall only be adopted on a voluntary basis and must not be mandated. Indeed, as in the context of STD, risk taking, whether or not related to disease transmission, had always been a feature of consensual sexual activities, which society had not sought to intervene in the past.
Such an argument based on individual autonomy and the doctrine of implied consent relies on the important assumption that potential victims are fully aware of the actual risks of infection. However, this is simply not true in the context of COVID-19. Given that COVID-19 does not express distinct physical manifestations, individuals cannot be presumed to know that the person standing next to him/her is a carrier of SARS-CoV-2. Therefore, consent to interacting with others in public cannot be presumed as consent to contracting COVID-19 in law. In fact, if victims are presumed to appreciate the risk of COVID-19 in any social encounters, there would exist no basis for liability of disease transmission based on fraudulent misrepresentation. This is because there cannot exist any deception to the risk of transmission in the first place if individuals are expected and presumed to know such risk themselves. As such, the presumption that victims would always be aware of the risk of transmission is a dangerous fantasy, which could render moot the liability for disease transmission through deception and risk failing to protect the most vulnerable victims.
In essence, neither informed consent nor implied consent based on considerations for individual autonomy is tenable in the context of COVID-19. In law, taking preventive measures such as wearing a mask is not a matter of individual risk-assessment under the doctrine of implied consent, but a means of discharging the duty of care not to transmit COVID-19 under the tort of negligence. Consideration for individual autonomy is nonetheless incorporated in the proportionality test assessing the standard of care.
In practice, causation might be the biggest hurdle in establishing liability for negligently transmitting COVID-19. At the time of this writing, SARS-CoV-2 is known to be capable of being transmitted through aerosols36 and fomites.37 This makes it costly, if not impossible, in practice to determine which particular droplet of SARS-CoV-2 had infected the victim. A patient might already have inhaled a non-tortious airborne nucleus of SARS-CoV-2 before contracting the droplet of SARS-CoV-2 from the negligent defendant. Therefore, the orthodox route in establishing causation through the Barnett 38 ’but-for’39 test is hard to satisfy in the context of COVID-19.40
Nevertheless, in Bonnington Castings v Wardlaw41 , the court had assisted claimants to overcome this evidential gap by finding causation in situations where it could be shown that the tortious exposure to the silica dust had materially contributed to the claimant’s harm, even if it was not the only cause. In the context of COVID-19, a research report published by the Lancet Infectious Disease Medical Journal on 1st June 2020 found that “(t)he mean viral load of severe (COVID-19) cases was around 60 times higher than that of mild cases”, with data indicating that “similar to SARS in 2002–03, patients with severe COVID-19 tend to have a high viral load and a long virus shedding period”.42 This finding not only suggests that the viral load of SARS-CoV-2 might be a useful indicator for assessing COVID-19 severity and prognosis, but also indicates, importantly, that the severity of COVID-19 symptoms aggravates in cumulo with SARS-COV-2 load. Therefore, similar to Bonnington in which the incremental nature of the claimant’s pneumoconiosiswas attributable to the cumulative effect of both the tortious and non-tortious silica dust, the cumulative nature of COVID-19 symptoms also makes the disease incremental, in which the disease aggravates with each exposure and is thus a divisible injury in law. Consequently, causation could be established on the basis that the defendant’s breach of duty of care not to transmit COVID-19 had made a material contribution to the claimant’s disease, even if the claimant could have first contracted SARS-CoV-2 from a non-tortious source. Causation based on this cumulative effect of divisible diseases is highlighted by Lord Keith in Bonnington itself:
Prima facie the particles inhaled are acting cumulatively, and I think the natural inference is that had it not been for the cumulative effect the pursuer would not have developed pneumoconiosis when he did and might not have developed it at all.43
However, a further difficulty inherent in the “Bonnington causation” lies in the apportionment of damages. In the context of COVID-19, there has been no acceptable scientifically supported evidentiary basis on which concurrent inhalation of both tortious and non-tortious SARS-CoV-2 could be apportioned to individual sources (such was the situation in Thompson v Smiths Shiprepairers (North Shields) Ltd44, in which conventional apportionment could be carried out by the court because the causal factors of the claimant’s injury operated consecutively rather than concurrently). This has consequently resulted in a dilemma whereby diseases like COVID-19 are divisible in theory but indivisible in reality.45 In this regard, given that English courts have well-established that apportionment of damages is not applicable to cases in which the defendant had materially contributed to indivisible injuries 46, this article therefore sees no prospect of any apportionment of damages in COVID-19 situations where practical apportionment is not feasible.47 In other words, from both the defendant’s and the claimant’s perspective, assessment of damages for theoretically divisible yet practically indivisible diseases like COVID-19 is in no way different from diseases that are purely indivisible, both in law and in practice. Therefore, until science could advance to a point at which the cumulative nature of COVID-19 could be separated according to the progressive severity of COVID-19 symptoms in response to each successive exposure factor, a defendant who negligently transmits COVID-19 to another, absent mitigating circumstances (e.g. the claimant’s own contributory negligence), would have to bear damages to the full extent of loss endured by the claimant.
This article has explored the potential of using the tort of negligence to establish civil liability in relation to the unintentional transmission of COVID-19. Departing from the conventional jurisprudence of other types of viral diseases, this article has argued for imposing a wide-ranging duty of care not to transmit COVID-19 on anyone who is “potentially infectious”. Nevertheless, it aims to calibrate the extent of such negligence liability through a proportionality test at the standard of care stage, balancing consideration for public health against the law’s commitment for individual autonomy. Importantly, neither the doctrine of informed consent nor that of implied consent can operate realistically in the context of COVID-19. And mask-wearing is not a measure of individual risk assessment, but rather a means of discharging the aforementioned duty of care. Lastly, although causation could be proved based on the Bonnington test of material contribution to the claimant’s disease, damages shall nonetheless be assessed without apportionment, given that COVID-19 is indivisible in practice despite being divisible by nature. Granted, the civil recourse theory48 of tort law does not imagine every COVID-19 victim to exercise their right of redress and seek the kind of legal recourse discussed in this article, save for the situations where wrongful deaths resulted from egregious instances of negligence. As a final note, the author wishes to highlight that in view of the dynamic development of the global COVID-19 pandemic, the standard of care will likely be constantly adapted in accordance with scientific development. New preventive measures, plausibly including vaccine acceptance amongst the population49, may influence what could potentially be deemed as acceptable in discharging the duty of care not to transmit COVID-19.
I am grateful for the feedback provided by Dr. Jo Braithwaite and Prof. Emmanuel Voyiakis from the London School of Economics and Political Science, and the anonymous editors of the LSE Law Review, on the early drafts of this article.
Julius Chen Ma
 Either to be used as an effective deterrence or in fact be used in negligence claims by COVID-19 victims, particularly in wrongful death claims.
 World Health Organisation, “WHO Director-General’s opening remarks at the media briefing on COVID-19”, 11 March 2020.
 J. Gardner, “What is Tort Law For? Part 1 - The Place of Corrective Justice”, Law and Philosophy, January 2011, Vol. 30, No. 1 (January 2011), pp. 1-50.
 A. Ripstein, Private Wrongs, Harvard University Press (2016).
 G. Calabresi, J. Hirschoff, “Toward a Test for Strict Liability in Torts”, The Yale Law Journal, Volume 81, Number 6, May 1972.
 See further S. Shavell, “Liability for Harm versus Regulation of Safety”, The Journal of Legal Studies, June 1984, Vol. 13, No. 2 (June 1984), pp. 357- 374.
 129 S.W. 431, 432 (Mo. 1910).
 543 So.2d 686 (Ala. 1989).
 Centers for Disease Control and Prevention, Smallpox, https://www.cdc.gov/smallpox/transmission/index.html.
 World Health Organisation, Herpes Simplex Virus, https://www.who.int/news-room/fact-sheets/detail/herpes-simplex-virus.
 World Health Organization, Modes of transmission of virus causing COVID-19: implications for IPC precaution recommendations: scientific brief, 29 March 2020.
 World Health Organisation, Coronavirus Disease 2019 (COVID-19) Situation Report 73, 2 April 2020.
 UK Coronavirus Act 2020, c. 7.
 World Health Organisation, Statistics Division (based on the United Nations Geoscheme).
 Section 2(2) of Coronavirus Act.
 Accurate as of 30th September 2020.
 Caparo Industries plc v Dickman,  UKHL 2. The House of Lords in Caparo (ibid) identified a three-part test which has to be satisfied if a negligence claim is to succeed, namely (a) damage must be reasonably foreseeable as a result of the defendant’s conduct, (b) the parties must be in a relationship of proximity or neighbourhood, and (c) it must be fair, just and reasonable to impose liability on the defendant (Lord Neuberger, ‘Reflections on the ICLR Top Fifteen Cases: A Talk to Commemorate the ICLR’s 150th Anniversary’, 06 October 2015).
 Prof. M.E. Kretzschmar et al. ”Impact of delays on effectiveness of contact tracing strategies for COVID-19: a modelling study”, the Lancet Public Health Medical Journal, 16 July 2020.
 The Lancet Infectious Disease Medical Journal, “Challenges of coronavirus disease 2019”, Volume 2 Issue 3 P261, 01 March 2020.
 See e.g. R v Parker  1 WLR 600.
  AC 850.
 45 Ohio St. 3d 314 (Ohio 1989).
 190 A.D.2d 463 (N.Y. App. Div. 1993).
 Law Commission, Reform of Offences against the Person: A Scoping Consultation Paper No 217 (2014), para 6.90.
 United States v. Carroll Towing Co, US Court of Appeals, 159 F.2d 169 at 173-4 per Learned Hand CJ.
 See n. 22.
 See n. 5.
 The consequences of transmission here are assessed based on the objective standard of a reasonable person, rather than a skilled medical professional.
 Statement by World Health Organisation Regional Office for Europe, “Older people are at highest risk from COVID-19, but all must act to prevent community spread”, Dr Hans Henri P. Kluge, 02 April 2020. Available at https://www.euro.who.int/en/health-topics/health-emergencies/coronavirus-covid-19/statements/statement-older-people-are-at-highest-risk-from-covid-19,-but-all-must-act-to-prevent-community-spread.
 World Health Organisation, “COVID-19: vulnerable and high-risk groups”, 25 March 2020.
 M. Weait, “Unsafe law: health, rights and the legal response to HIV”, International Journal of Law in Context, P535–564 (2013).
 L. Cherkassky, ‘Being Informed: The Complexities of Knowledge, Deception and Consent When Transmitting HIV’ (2010) Journal of Criminal Law 242 at 248.
 See also S. Ryan, “Disclosure and HIV Transmission”, The Journal of Criminal Law 2015, Vol. 79(6) 395–410.
 See e.g. Collins v Wilcock  3 All ER 374 on implied consent.
 World Health Organisation, Transmission of SARS-CoV-2: implications for infection prevention precautions, 9^th^ July 2020. Available at https://www.who.int/news-room/commentaries/detail/transmission-of-sars-cov-2-implications-for-infection-prevention-precautions.
 Ibid, paras 13, 14.
 Barnett v Chelsea & Kensington Hospital Management Committee  2 WLR 422.
 The orthodox ‘but-for’ causation requires that the defendant is negligent only if her breach of duty of care more likely than not a cause of the claimant’s loss, i.e. on a balance of probabilities.
 Of course, the author does not rule out the possibility that that the traditional ‘but-for’ causation might be satisfied in certain exceptional circumstances, such as when the claimant had not interacted with any other plausible sources of infection except with the negligent defendant.
  AC 613.
 Lagen Wan et al. ”Viral dynamics in mild and severe cases of COVID-19”. The Lancet Infectious Disease Medical Journal, Volume 20 Issue 6 P656-657, 01 June 2020.
  AC 613 (HL) at 626 (per Lord Keith).
  1 All ER 881.
 See also S. Green, “Causation in Negligence”, Chapter 5 (Hart Publishing 2015), P96-98.
 See, Dingle v Associated Newspapers  2 QB 162 (CA) at 188 (per Devlin LJ), Hotson v East Berkshire Health Authority AC 750 (HL) at 783 (per Lord Harwich) and J Smith, ‘Causation – the Search for Principle’  Journal of Personal Injury Law 101, 103.
 If science has advanced to a stage in which COVID-19 can become divisible in practice, then causation based on the orthodox ‘but-for’ test would likely apply. However, given the urgency of the global health crisis, this might not be the current priority of the scientific community.
 J. Goldberg & B. Zipursky, “Civil Wrongs and Civil Rights”, Recognising Wrongs, Harvard University Press (2020).
 World Health Organisation, “Vaccine hesitancy: A growing challenge for immunization programmes.” (18 August 2015) Available at: https://www.who.int/news-room/detail/18-08-2015-vaccine-hesitancy-a-growing-challenge-for-immunization-programmes.