Vaccination priorities and science


Sir, – The definition of risk is the two-component probability of an event happening multiplied by the severity of the outcome (which in itself is a probability).

For example, if one applies for a job, there is firstly the probability of being offered the job followed by the probability that the job may turn out to be something less than expected. There could be a small probability that it is really bad, or a lesser probability that it might be tolerable but not very pleasant.

Similarly with Covid, there is an exposure component and a morbidity component.

First, there is the occupation-based probability of becoming infected, which is higher for some professions such as teachers, gardaí and retail workers, as they are exposed to potential infections every day.

Then there is the age-based component which comprises the following; a small probability of a severe outcome such as death, a greater probability of being on a ventilator, an even greater probability of a hospital stay, and the most likely outcome of a mild illness. The probability of getting “long Covid” falls somewhere in between as an additional outcome.

The teachers are talking about the first occupation-based component while the Minister is talking about the second age-based component of the Covid risk.

I may be older than the teachers but my risk profile has to be lower as I am not exposed on a daily basis to potential infections as they are. – Yours, etc,




Co Wicklow.

Sir, – The use of the word “science” by Government Ministers to justify the change in the vaccination programme is misleading.

That older people are at greater risk of dying when sick with Covid-19 than younger people also with Covid-19 is a statistical fact, obtained from analysis of the data.

The decision on which sections of society are prioritised should also include the probability of catching the disease, which depends on a number of factors associated with its transmission.

The science is that transmission of the disease is via airborne droplets emitted by carriers when breathing, coughing and sneezing. The risks of catching the disease are increased the closer people are together, the greater the number in close proximity, the greater the length of time they stay together, the worse the ventilation, and when personal protective equipment PPE is not used or is inadequate. These risks are not age-related.

Avoidance and mitigation of these risks is at the heart of all the Covid-related advice from the World Health Organisation and national health organisations, and the guidelines that have (or should have) become embedded in our daily activities. Since teachers, especially special needs assistants, and gardaí, have to work in high-risk situations where they cannot, because of the nature of their work, adhere fully to the guidelines, they should receive a higher priority for vaccination than those who can adhere fully. – Yours, etc,


Cratloe, Co Clare.