What is vaccine efficacy? Experts break it down


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(WETM) – “If you are vaccinated, you have a much much much less chance of getting sick with COVID-19,” Dr. Justin Nistico, infectious disease expert at Arnot Health, said.

Vaccine efficacy is a complicated topic and understanding clinical trial data can be confusing. In the FDA Emergency Use Authorization application, each vaccine manufacturer included a graph documenting the clinical trials.

View the Pfizer, Moderna or Johnson & Johnson applications.

This graph shows the effectiveness of each vaccine when compared to the placebo.

“In Phase 3 clinical trials, there are two groups of people that are matched as closely as possible by age, gender, and demography to make equal,” Dr. John Moore, professor at Weill Cornell Medicine added. “The only differences are one group gets the vaccine and the other group gets the placebo shot.”

To understand these graphs, we must identify the variables. The flat lines represent the participants who received vaccinations. The incline represents the participants who received the placebo shot. The bottom axis shows time while the vertical axis shows number of participants.

As the lines diverge from one another, it is understood that the vaccines are working. The incline shows participants who did not receive the vaccine have a higher chance of contracting COVID-19 than those who were vaccinated. 19 out of 20 participants who were vaccinated did not contract the virus.

“If you look at that graph, you’ll see that nothing happened between the two lines for about 12 to 14 days,” Dr. Moore added.

It shows the vaccine effects do not occur right away. It takes a few days before any degree of immunity is seen.

On day 42, the vaccine manufacturers tested efficacy. At this point in the trial, Pfizer and Moderna determined their vaccinations were 95 percent effective. Johnson & Johnson said their vaccine was approximately 70 percent effective.

“That is the published measure, but you can see it doesn’t make any difference. The efficacy is maintained for a long period of time,” Dr. Moore continued. “For protection against severe disease and death, all three vaccines were highly effective and there was no real difference between them.”

This data comes from controlled clinical trials, but scientists are beginning to study the real-world effects of the vaccine. Will the real-world data match the trial numbers?

“The real world is supporting what was seen in the phase three trials which is extremely good,” Dr. Moore said.

Several countries are monitoring the efficacy of the vaccines as they administer the shots. In a Pfizer study in Israel, the vaccine efficacy data from the trials are matching the immune responses from individuals.

“If we really started this fight with COVID-19 with these vaccinations, I think it’d be a different story to some degree. We definitely would see an improvement in how many cases we are seeing,” Dr. Nistico added.

Experts believe the vaccines will continue to protect individuals for months if not years. This data is being gathered daily. Participants from the original clinical trials in 2020 have been vaccinated for nearly six months. Monitoring their progress will provide more information as scientists move forward in the vaccination process.

“It will be sustained for many many months, perhaps a year or perhaps longer,” Dr. Moore conclude.

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