Waning of efficacy and interpretation

A lot of controversy has come up with the boosters for the COVID-19 vaccines and efficacy. The Israeli study on efficacy comparing people vaccinated last year to people vaccinated this year seemed to indicate the efficacy was waning over time. The clarity around the issue is confusing due to biases like selection biases and lack of properly designed studies around the issues. There is also confusion about what is being discussed and evaluated in terms of efficacy, is it symptomatic disease or severe disease?

According to an article in Science (Vogel, 2021), the author stated…


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…


As we have heard or know, COVID-19 research, especially in early 2020, was filled with observational studies, many of which were potentially underpowered, but it turns out, even randomized controlled trials. Sample size estimation went out the window. Even Lee (2020) published two articles about this situation. He reviewed articles published between January 1 to March 25, 2020. Of the 374 articles he reviewed, only 4 were clinical trials. Even amongst those trials, the sample size estimations were found to be unacceptable. His suggestion was for these studies to include a statistician. …


With all the news about vaccine efficacy and how long the effects of the vaccine will last, it is interesting to wonder how the statistical models to detect such effects are designed for such research . In the Khoury et al paper (2020), they do consider the decay of antibody titers over time in their cohort of subjects, through a linear mixed effects model with exponential decay. Their interpretations of these decaying effects from the model are somewhat unclear and are somewhat muddied by their other main results in their paper. …


Re-analyses on vaccine efficacy in COVID-19 research

Much of the news these days focuses on vaccine efficacy rates being re-updated due to various new COVID-19 variants coming out often, originating in different countries, like delta (B.1.167.2) from India and lambda (C.37) from Peru. These vaccine rates are being re-updated and re-analyzed, but not very much is discussed about how these rates are constantly analyzed and assessed. What population of data ends up being used for re-analyses? If the data is used from another country, how can the results be generalized to the United States?

The Saul et al article below…


Bayesian methods used in COVID-19 research

During the times of uncertainty in statistical methods used in COVID-19 research. Were Bayesian methods employed much in these contexts? Yes they were here and there but probably once again, just like in regular research, the methods were not used very often or were put as secondary analyses, possibly out of fear of the public not understanding the methods. They also did not seem to be used in the comparisons of vaccinated and control groups in clinical trials of the major vaccines that have been in the news and even administered.

The question is…


by Usha Govindarajulu | Jun 9, 2021 | Biostatistics, Blog, Healthcare, Professor, Usha Govindarajulu

P-values and vaccine efficacy

As the companies continue to re-evaluate vaccine efficacy against new variants, have they discussed p-values? Are they analyzing re-updated data again and again and correcting for inflation of the Type I error rate?? Given the p-value controversy in statistics and the controversy of vaccine efficacy, statisticians have to wonder if these topics have been considered together. Even if this topic is being considered, it is hardly discussed. One can only imagine it must have been very difficult to plan these trials and…


COVID-19 challenges of publishing statistically relevant studies

COVID-19 is a tricky period in which to attempt to publish new studies. Criticism came from reviewers and those reading the articles whether or not one showed negative results or positive results from the study. In fact, due to the ongoing situation with the pandemic, much criticism has been given to any potential positive results since other articles had been published with results that were not accurate. It has been a very difficult time period then for perhaps well designed studies even to get published due to the bias in the media against…


Can one control for selection bias in analyses? Unfortunately selection bias is inherent to many studies, even the gold standard clinical trial designs, but these problems can be attempted to be controlled for in analyses. In COVID-19 research especially, there are selection bias issues related to selection of patients in studies, often the less sicker of patients and also those who are willing to volunteer. All these and other issues can cause selection bias in COVID-19 research. …


Missing data

Missing data is a phenomenon that happens in almost all studies whether in observational or clinical trials. It most often occurs in studies that involve long-term follow up, where people miss different follow up visits or exit the study for various reasons. This results in problems with analyzing data, especially if there is a lot of missingness or if there is a pattern to the missingness and it did not occur randomly.

Missing data happened in COVID-19 data and continues to do so. Initially missing data happened in the beginning when it was hard to collect all measurements…

Usha Govindarajulu

Usha Govindarajulu is a writer and biostatistician . www.UshaGovindarajulu.com

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store