Issues in COVID-19 research and statistical analyses (Part XI)

Understanding percentages and efficacy

August 18, 2021

Recently, there has been a lot of news about COVID-19 research tied to the studies conducted in Israel since they have such a high rate of vaccination and since they themselves have conducted several analyses which are very timely for understanding the changes in efficacy of the vaccines, mainly of the Pfizer and Moderna mRNA ones. However, when the general public reads these news, there is often cause of confusion amongst them.

For some example, when posting a general question on a major social medial platform about why people were still avoiding the vaccine when almost all hospitalized were unvaccinated, one person responded about the following: “Israeli Health Ministry recorded on Sunday 1,398 new COVID-19 cases with 108 people in serious condition, 20 of whom are on ventilators and 25 are in critical condition. Moreover, there are 199 coronavirus patients in Israeli hospitals. According to the Health Ministry’s data, out of the 108 patients who suffer severe symptoms 75 are inoculated with one or two jabs.” Although I was unable to validate this exact data online, depending upon the way this person decided to interpret the percentages, there could be a very high rate of breakthrough infections amongst vaccinated, especially if those with only one jab were counted in that.

It is starting to become clear that breakthrough cases amongst those vaccinated can lead to more serious outcomes. It was reported in Science Magazine, an AAAS publication, on August 16 that on August 15, 514 Israelis were hospitalized with severe or critical COVID-19, and of those 514, 59% were fully vaccinated. Amongst those fully vaccinated, 87% were age 60 or older. It is clear then that the vaccine efficacy breaks down with age and comorbidities. However, Uri Shalit, a bioinformatician at the Israel Institute of Technology (Technion) who has consulted on COVID-19 for the government said, “There are so many breakthrough infections that they dominate and most of the hospitalized patients are actually vaccinated,” As of today, 5.4 million Israelis have received their 2nd dose. Therefore, the number of critically ill who have been fully vaccinated is so well below 1%. It was impossible to find the total number of breakthrough cases to also calculate this percentage so we have to rely on what they have reported. It is so important to understand how to calculate the correct percentages.

Keywords: COVID-19, vaccines, efficacy, Israeli study, percentages, Usha Govindarajulu

Usha Govindarajulu is a writer and biostatistician .