THE EDITOR: In all the talk about vaccination two things keep playing in my mind. One is the word 'pandemic' and the other is the phrase 'herd immunity.'

We are reminded every hour of every day that we are in a pandemic and that we need to achieve herd immunity. What is a pandemic? According to the US Centre for Disease Control and Prevention, a pandemic is '…a disease outbreak that has spread across multiple countries and continents and usually impacts many people. The classification of 'pandemic' comes when a disease affects the global population.'

What is herd immunity? According to one definition put forward by the Mayo Clinic in the US, 'Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person to person unlikely. As a result, the whole community becomes protected - not just those who are immune.'

How is this herd immunity achieved? Herd immunity can be achieved through infection or through vaccination. 'Herd immunity can be reached when enough people in the population have recovered from a disease and have developed protective antibodies against future infection.'

Herd immunity can also be achieved when enough people have been vaccinated against a disease and have developed protective antibodies against future infection.

It is said that the percentage of the population that needs to be immune to achieve herd immunity varies with the particular disease. Some diseases, like small pox, may require 95 per cent of the population to be immune.

Various figures have been put forward to achieve herd immunity from covid19 virus. A popular figure was 70 per cent of the population although the figure varies. The latest one put forward by the chief medical officer (CMO) is 80 per cent. This is okay because fresh data about covid19 is being gathered every day.

We are told that herd immunity can be achieved if a percentage of the people of TT are vaccinated. The prime minister in his latest buff of the citizens talks about achieving herd immunity in the school system. The CMO talks about herd immunity in particular areas of the country.

While figures are put out every day about how many have been vaccinated and how many are recorded as having recovered from the disease, we have no idea how many have been infected because we have not engaged in widespread testing.

It is stated that most people who have been infected by the virus presented no symptoms. There may be tens, even hundreds, of thousands of people who have immunity because of natural infection, but we have no way of knowing.

Another problem is that, so far, according to the Mayo Clinic, 'It's not clear how long you are protected from getting sick again after recovering from covid19. Even if you have antibodies, it's possible that you could get covid19 again.'

What bothers me though is how can we achieve herd immunity in the school system or in the country as whole when we are dealing with a pandemic which is a worldwide phenomenon? The vast majority of people on