Vaccines are not 100% effective; but they work

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

24 October 2021

Why are people who have been vaccinated against Covid-19 getting the disease? Doesn’t this mean that the vaccine is not working? So-called “anti-vaxxers” are using this fact to further their campaign to convince the public not to get the jabs. Unfortunately, this is a good illustration of how incomplete data can be used to mislead.

The statement that “people who have been vaccinated against Covid-19 are getting the disease” is true but it is incomplete. It does not contain any numbers; and, as we all know, numbers don’t lie! So far, two vaccines have been administered in Kenya. These are: Oxford-AstraZeneca and Moderna.

No medicine has 100 per cent efficacy and these are not different. Before the vaccines were approved by health authorities around the world, they were tested and the results showed that the Moderna product was 90 per cent effective while the Oxford-AstraZeneca was 76 per cent.

What this means is that, if the Moderna vaccine is injected in 1,000 people, 900 will get protected while 100 will not. It is impossible to know which individuals will fall into which group. The corresponding numbers for the Oxford-AstraZeneca would be 760 and 240 respectively.

Now, at the time of writing this article, about 1.3 million people in Kenya had been fully vaccinated with two doses and another 3.4 million had received the first dose. At this point, we have approximately equal numbers of vaccinations by each of the two types of vaccines, therefore, it is safe to assume that he combined effectiveness is about 85 per cent.

So, out of the 1.3M fully vaccinated people, we should expect that about 1.1M will gain immunity from the disease leaving 200,000 exposed. Now 200,000 is not a small number; so, there is a good chance that you will come across a case of a fully vaccinated person who contracted Covid-19.

So, is it worthwhile to get vaccinated? The story of smallpox might help one decide. This disease was eradicated from the face of the earth in 1980 – over 30 years ago. This was achieved through a spirited vaccination campaign. The vaccines used were about 90 to 95 per cent effective. Clearly then, we don’t need a 100 percent effective vaccine to stop the spread of Covid-19, or even to eradicate it completely. What we need is mass vaccinations – so, if you haven’t been vaccinated yet, go and get now!