Juan Gérvas points out that we do not have enough data about the prevention of virus transmission to justify mandatory COVID-19 vaccination for health care workers.

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A recent article in the Canadian Medical Association Journal by Collen Flood, Bryan Thomas, and Kumanan Wilson has proposed mandatory vaccination against COVID-19 for health care workers. The authors argue that, “An effective vaccine provided to all health care workers in Canada will protect both the health workforce and patients”. The problem with this proposal is that we do not know whether all COVID-19 vaccines will prevent transmission (and thus produce herd immunity). Will the vaccines protect only those who get vaccinated, or will the benefits also accrue to the population?

Vaccines are drugs that protect against infectious diseases. As a general rule, they protect those who get vaccinated by producing personal immunity. In addition, some vaccines protect the community by producing herd (population) immunity. But there are exceptions. Some vaccines do not prevent transmission.

For example, there is evidence that the acellular pertussis vaccine currently in use in many countries does not prevent transmission of pertussis. People who are vaccinated against pertussis may show no symptoms of the disease, but can still transmit the infection.

Photo Credit: Jernej Furman/flickr. Image Description: A vial of Covid-19 vaccine with a stethoscope.

The measles vaccine is an example of a vaccine that produces herd immunity. It requires about 95% uptake, however, for there to be herd immunity. This vaccine benefits those who are vaccinated, since it produces personal immunity against a very infectious agent, but it also benefits those who cannot be vaccinated, such as immunocompromised patients. This benefit, herd immunity, is achieved by interrupting the transmission of the measles virus.

We have only preliminary data regarding whether vaccines against COVID-19 reduce the transmission of the virus, and therefore whether the vaccines can produce herd immunity. There is still no definitive data.

Therefore, the public health advice is to get vaccinated and to maintain hygiene measures as if you had not been vaccinated (hand washing, physical distancing, avoiding overcrowded and poorly ventilated places and the use of a mask in such situations).

However, vaccines are often presented as a public good, as an obligation because “it protects you, and you protect others.” This well-intentioned advice is contentious when we do not know if the vaccine interrupts the transmission of the virus (SARS-CoV-2) and for this reason at the same time public health officials recommend maintaining hygienic measures as if one had not been vaccinated.

Telling health professionals to take COVID-19 vaccines so that they don’t infect patients, then claiming that those vaccines might not prevent transmission is a misguided public health strategy. We are not yet certain which vaccines can prevent people from becoming infected or infecting others so it is possible that vaccinated health professionals, without getting sick themselves, could give the virus to unvaccinated people.

We could apply the precautionary principle if we accept that the uncertainty will take time to resolve and that it would be prudent to vaccinate now in the hope that the vaccine will decrease transmission in the future. In this sense, the precautionary principle justifies the strategy of vaccinating the population and health care workers. But this precautionary approach does not justify mandatory vaccination of these professionals.

We cannot apply the precautionary principle to justify mandatory vaccination of health care workers because the risk of spread could increase if, after vaccination, people mistakenly act as if they are no longer capable of harboring contagion. In the case of healthcare workers this could be serious as it would mean that they would become “contagious agents” (in a sense transforming COVID-19 into a nosocomial infectious disease).

There is another problem as well. As the science and health journalist Tara Haelle writes, “there’s good reason not to say the COVID vaccine will prevent transmission until we actually have robust data to say so. The worst thing we can do is suggest it does, find out it doesn’t – and lose public trust”. We should not claim that vaccines against COVID-19 prevent transmission when we do not know whether they do. Flood, Thomas, and Wilson appear to make this claim in their CMAJ article. Public trust is at stake.

As long as we do not have more knowledge, it lacks scientific and ethical justification to demand compulsory COVID-19 vaccination for health care workers. The proposals for mandating COVID-19 vaccines are unethical.

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Juan Gérvas is a retired rural general practitioner with Equipo CESCA, Madrid, Spain, and an ex-Visiting Professor at the Johns Hopkins School of Public Health (1991-2003), as well as at the National School of Public Health in Madrid, Spain (2004-2020). @JuanGrvas