LETTER | Vaccination statistics worth a thousand words

Dr Song Beng Kah


LETTER | There is a video going around on WhatsApp concerning 12 questions and answers to consider before getting vaccinated. These questions were structured and phrased in such a way that all answers given are “No” or “Maybe”, for the purpose of persuading the public about the “uselessness” of the Covid-19 vaccines. 

Two of the questions include “If I get vaccinated, at least I won't be contagious to others - right?” and “If I get vaccinated, I can protect 100 percent of people I come in contact with?”. Both the answers are given are “NO”, and it says that “The vaccine doesn’t stop transmission”. 

To many laypeople, these Q&As sound convincing and logical, since the conclusions provided in the messages are “The vaccine does not guarantee you won’t get it, and does not stop you from passing it on to others”.

Unfortunately, like many other pseudoscience messages and videos that have spread widely on social media platforms, this is another hoax, which applies a type of bad argument named “castle of cards”. 

In such a bad argument, the messenger uses some nicely ordered and interconnected right and wrong reasons along with unwarranted leaps in between, to come out with a certain conclusion that the messenger wants people to believe. If the audience could point out the incorrect reasons (cards), the argument and conclusion (castle) will collapse right away.

Last week, this 12-Q&A video and messages echoed what the mass media reported on 40 Malaysian healthcare workers infected after the Covid-19 vaccination. This caused quite a commotion among the public and many again wondered why should we get vaccinated since we will still get infected by the virus. 

The Ministry of Health (MOH) has correctly clarified that that vaccination protects an individual from getting seriously ill and dying from Covid-19. But can Covid-19 vaccines actually stop transmission? The good news is that scientists have found the answers.

There are a few research findings recently published in international research journals presenting some statistics on the real-world vaccine effectiveness, which serve as timely responses to the question. 

For instance, preliminary analyses from the US demonstrate that a two-dose Pfizer-BioNTech or Moderna mRNA vaccination is effective against both symptomatic and asymptomatic infections, with vaccine effectiveness around 90 percent. 

In the UK, the effectiveness of the Pfizer-BioNTech vaccine is up to 89 percent for the elderly over 80 years old. The vaccination programmes in Israel have also demonstrated that the same mRNA vaccine achieved a similar efficacious level against the virus at 92 percent for the general adult population. 

For Denmark, statistics show that the effectiveness is 64 percent and 90 percent for long term care facility residents and caregivers respectively. See here, here and here.

The next question would be: What does 90 percent efficacy tell us? The common misunderstanding among the public is that “90 percent means 9 out of 10 vaccinated people won’t get infected”.

In order to understand the definition of “vaccine effectiveness” correctly, we need to know this equation:

(Attack rate of unvaccinated people - Attack rate of vaccinated people) / Attack rate of unvaccinated people X 100

Bear in mind that only people who received a two-dose vaccine are considered vaccinated. Clinical trials of the Pfizer-BioNTech mRNA vaccine found that only 0.04 percent of the vaccinated people (i.e. 4 out of 10 thousand) were infected by the virus, whereas the unvaccinated group recorded a 20 times higher rate at 0.8 percent (i.e. 80 out of 10 thousand). 

Putting these figures into the equation will give us (0.8-0.04)/0.8×100 = 95 percent, which is what has been frequently reported in the media for the efficacy of the Pfizer-BioNTech mRNA vaccine.

Taken together, the scientific evidence and statistics tell us that these vaccines are effective in stopping transmission of the virus and lowering the infection rate among the community.

Indeed, vaccination statistics are worth a thousand words!

The views expressed here are those of the author/contributor and do not necessarily represent the views of Malaysiakini.