[SOLVED SAMPLE] Assignment 2 Part 2: Critical Review

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Objective: To critically evaluate epidemiologic literature by assessing methodologies, interpreting study results, and challenging findings.

Instructions:

• Write a brief 3-page critique of the attached paper, “Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: final results from the Guinea ring vaccination, open-label, cluster-randomised trial,” by Henao-Restrepo et al. You should consult the below guidelines for your critique, addressing the various aspects as appropriate. You do not need to answer every point, but your critique should be comprehensive enough to demonstrate your understanding. Your critique should be structured as an essay, double-spaced, 3 pages, and have 1” inch margins.

How to Review a Paper (modified version of Dr. Pam Factor-Litvak’s version):

1. What is the study question?
2. Identify the design of the study.
   1. Is the design appropriate to answer the study question?
3. Identify the source population.
   1. Does the study population reflect the source population?
4. Identify the participants.
   1. How were participants selected?
   2. Was there attrition during the study?
   3. What are the comparison groups? Are they reasonable?
5. Identify the exposure and outcome measures and the key covariates.
   1. What is the key exposure measure? Is there potential for bias in its collection?
   2. What is the key outcome measure? Is there potential for bias in its collection?
   3. What are the key covariates? Is there potential for bias in their collection?
   4. For how long were the participants followed?
   5. Was there any potential bias from the observers?
   6. Was there any potential bias from the participants?
6. Identify the main statistical analytic method.
   1. Are sufficient preliminary data presented?
   2. Is the choice of statistical model appropriate?
7. Evaluate the interpretation of the findings
   1. Do the investigators focus on biological significance or statistical significance?
   2. What are the strengths of the study?
   3. What are the limitations of the study?
   4. In your opinion, is there evidence of a causal interpretation using Hill’s criteria or another approach?
   5. Given any problems identified, do the strengths of the study outweigh its weaknesses?
   6. Are there any policy implications?

 

[FULL ANSWER]

Article Critique: “Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: final results from the Guinea ring vaccination, open-label, cluster-randomised trial.”

Not all published articles are should be used to inform practice (Greenhalgh, 1997). In that regard, the following essay will comprise brief critique of “Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: final results from the Guinea ring vaccination, open-label, cluster-randomised trial,” by Henao-Restrepo et al.

The research has no particular question, but aimed at testing the effect of rVSV-ZEBOV in prevention of Ebola virus disease. It adopted a cluster-randomised controlled trial (Henao-Restrepo et al., 2017). Since the research falls in the field of therapy (testing efficacy of drug treatments), a randomised control trial is the most recommended design (Greenhalgh, 1997). Therefore, a cluster-randomised controlled trial is appropriate for achieving the aim of the study. The source population comprised people infected with Ebola from Guinea. The study participants were a reflection of the source population as it involved index cases of the Ebola virus disease, their contacts, and contacts of contacts, even those who were absent at the time of recruitment. The participants were enumerated as clusters or rings of epidemiologically linked individuals. The individuals were identified through a sustained surveillance for laboratory confirmed Ebola virus disease cases. There were two separate cases for identification of index cases as well as contacts and contacts of contacts. There was no attrition during the study. In fact, the scope of participants was expanded, with children between 6 and 17 years within the identified rings getting the vaccine. The comparison groups include eligible individuals assigned to the immediate vaccination against contacts and contacts of contacts who received the delayed vaccination. The groups are reasonable as the outcome of the comparison would likely be the efficacy of the vaccination, which aligns with the primary aim of the study.

Safety (lack of an adverse event) was the key exposure measure. The participants were followed and watched for 30 minutes from the time of vaccination as well as at their homes. The possibility of an adverse event was then examined and judged by the study physicians. No bias was identified in the collection of exposure measure. According to Henao-Restrepo et al. (2017) the main outcome was a laboratory verified Ebola virus disease case, with outcome measures being blood sample testing and post-mortem results. No bias was apparent in the collection of either. The participants, a total of 5837 including the children were followed for 84 days. The observers only noted a recruitment bias, which they addressed by terminating the enumeration of participants prior to cluster allocation. On the side of the participants, however, there was no notable bias. Mansournia et al. (2017) state that randomization prevents bias because there is no comparability between group, and such a benefit becomes more apparent where there is an “intention-to-treat.” The current study embodies that principle, which is perhaps the main reason for lack of common biases.

Statistical analysis was done through R in conjunction with an independent statistician who was not part of the trial. Sufficient preliminary data was presented and interpreted. The data showed that the vaccine was 100% effective. Given the data, delayed-vaccination was terminated. These results are consistent with World Health Organization [WHO] (2019), which found that the vaccine was 97.5% effective. The choice of statistical model equally seemed appropriate. A randomised study by Robertson et al. (2017) also applied the method in calculations. A quick check through the internet for other randomised studies reveal the use of the same statistical model, thus, implying that it could be the best for such investigations. Even so, an intention-to-treat (ITT) analysis has also been proven as a worthy alternative (Egbewale, 2015). It solves the protocol violation problem that is common in randomised control trials.

While the findings are analysed statistically, they reveal that the investigators greatly focused on biological significance. All the statistical data are linked with efficacy of the vaccine as well as potential adverse events linked with its use. The overall interpretation of the findings showed that the vaccine offered significant protection from the Ebola virus disease. The primary strength of the study, just like with other randomised controlled trials, is excellent internal validity (Booth & Tannock, 2014). As already noted, the study is largely free of bias and, as such, has a high level of accuracy and reliability. The study design facilitated establishment of causation, and measurement of patient-reported outcomes. Booth and Tannock (2014) noted that RCTs are capable of providing evidence of efficacy, but the results have limited applicability to practice because of the difference between participants and patients in routine practice. There is evidence of causal interpretation using Hill’s criteria especially with regards to biological gradient. Hill holds that if there’s response to a dose, then there is a causal association (Fedak et al., 2015). The participants responded positively to the vaccine doses, leading to a conclusion that it is effective. Only one limitation of the study was identified against three strengths. The limitation can easily be overcome by tailoring the findings to match specific routine situations. Therefore, the weakness is somewhat insignificant compared to the strengths. Regarding policy implications, Henao-Restrepo et al. (2017) note that the trial was designed to generate meaningful data for efficacy, which will be used to underpin the use of the vaccine in actual practice.

The research succeeded in proving the efficacy of the vaccine by using the most appropriate research design. While the design had some weaknesses, the strengths outweigh these limitations. Therefore, the investigation can satisfactorily inform practice.

References

Booth, C. M., & Tannock, I. F. (2014). Randomised controlled trials and population-based observational research: Partners in the evolution of medical evidence. British Journal of Cancer, 110(3), 551–555. https://doi.org/10.1038/bjc.2013.725

Egbewale, B. E. (2015). Statistical issues in randomised controlled trials: A narrative synthesis. Asian Pacific Journal of Tropical Biomedicine, 5(5), 354–359. https://doi.org/10.1016/s2221-1691(15)30367-1

Fedak, K. M., Bernal, A., Capshaw, Z. A., & Gross, S. (2015). Applying the Bradford Hill criteria in the 21st century: How data integration has changed causal inference in molecular epidemiology. Emerging Themes in Epidemiology, 12(1). https://doi.org/10.1186/s12982-015-0037-4

Greenhalgh, T. (1997). How to read a paper : Getting your bearings (deciding what the paper is about). British Medical Journal, 315(7102), 243–246. https://doi.org/10.1136/bmj.315.7102.243

Henao-Restrepo, A. M., Camacho, A., Longini, I. M., Watson, C. H., Edmunds, W. J., Egger, M., Carroll, M. W., Dean, N. E., Diatta, I., Doumbia, M., Draguez, B., Duraffour, S., Enwere, G., Grais, R., Gunther, S., Gsell, P.-S., Hossmann, S., Watle, S. V., Kondé, M. K., … Kieny, M.-P. (2017). Efficacy and effectiveness of an rVSV-vectored vaccine in preventing Ebola virus disease: Final results from the guinea ring vaccination, open-label, cluster-randomised trial (Ebola ça suffit!). Lancet (London, England), 389(10068), 505–518. https://doi.org/10.1016/S0140-6736(16)32621-6

Mansournia, M. A., Higgins, J. P. T., Sterne, J. A. C., & Hernán, M. A. (2017). Biases in randomized trials. Epidemiology, 28(1), 54–59. https://doi.org/10.1097/ede.0000000000000564

Robertson, W., Fleming, J., Kamal, A., Hamborg, T., Khan, K. A., Griffiths, F., Stewart-Brown, S., Stallard, N., Petrou, S., Simkiss, D., Harrison, E., Kim, S. W., & Thorogood, M. (2017). Statistical analysis methods. Health Technology Assessment, 21(1). https://www.ncbi.nlm.nih.gov/books/NBK409050/

World Health Organization [WHO]. (2019). Preliminary results on the efficacy of rVSV-ZEBOV-GP Ebola vaccine using the ring vaccination strategy in the control of an Ebola outbreak in the. WHO. https://www.who.int/csr/resources/publications/ebola/ebola-ring-vaccination-results-12-april-2019.pdf