Understanding Vaccines – What does efficacy rate really mean?

We have all heard the big statistic when it comes to vaccines, BioNTech has an efficacy rate of ~95%, and SinoVac has an efficacy rate of ~50%, but does that mean that the Sinovac vaccine is worse than the BioNTech one?

To understand this, we must first understand what the efficacy rate means. Vaccine trials usually involve thousands of people, for this example let’s say 20,000 people are involved in this trial. Half are given the vaccine, half are given a placebo. These people are then released into the world. Afterwards these people are called back where they are tested to see if they have contracted Covid 19.

The efficacy rate is then calculated by comparing the amount of people who contracted covid 19 from both groups. In our example, if 100 people from the vaccinated group contracted covid 19, and 5000 people contracted covid 19 in the placebo group after 7 days, the vaccine would have an efficacy rate of 100/5000 = 0.02 = 98%

5000 tested positive in placebo group compared to 100 tested positive in vaccinated group.
People in the vaccinated group are therefore 98% less likely to contract covid 19 compared to the placebo group after a period of 7 days.

This is what the efficacy rate is, it is no more than a comparison between the vaccinated and placebo groups of the trial. This also means that the circumstances surrounding the trial will have a huge effect on the efficacy rate.

Now lets look at the trials for Biontech and Sinovac.





Interval between last dose and covid 19 test

14 days

7 days

Major Trial locations

Brazil, Chile, Turkey, Indonesia

USA, Germany

Time of Trial

August 2020 – October 2020

July 2020

Approximate Total amount of people involved in major trials

~ 46600 people including ~16000 healthcare workers

~43000 people


Just from a quick glance we can see they were quite different. Lets break each aspect down and see how this may affect efficacy rates.

Time Interval.

Sinovac waited 7 days longer than Biontech to test their participants. This gave both the control group and the vaccinated group longer to contract covid 19. This means that there is a greater variability in a longer trial, as participants are more likely to engage in a variety of activities. For instance compare how many times you go out to eat in 2 weeks compared to 1.

Major Trial Locations

Sinovac was tested in Latin America, Turkey and Indonesia, compared to BionTechs USA and Germany. Both Brazil and USA have suffered from very high covid19 infection rates, showing that the trials took place in meaningful locations to test their efficacy.

Time of Trial.

The Sinovac trials took place in the winter months of 2020, compared to the Biontech’s trials which took place in the summer. The winter months saw the global peak in covid 19 cases, meaning that the Sinovac trial took place in a period of time where you were much more likely to catch covid19 regardless of your activities.

Trial participants

Both the Sinovac and Biontech trial had around 40-50 thousand participants, however the Sinovac trial included a large proportion of health care workers, which have a far higher probability of coming into contact with covid 19.

So what does this all mean?

It means that the circumstances surrounding both trials are completely different. To compare efficacy rates is inherently meaningless as the test conditions could not possibly be the same. There is however one key message that we can see. No matter what vaccine you choose, the science shows that you will be better off than someone who has not taken the vaccine. So, speak to your doctor, follow their advice, and sign up for your vaccination soon.

It also means that you still have a chance to catch and spread covid19 even if you are vaccinated. Stay safe and stay comfortable with an Airizy Protetra mask. Shop here.

If you are having doubt about vaccination, please contact a licenced physician. This article aims to explain the meaning behind a vaccine’s efficacy rate and is in no means medical advice. The details regarding the trials of both Sinovac and Biontech offered in this article are by no means intended to be a clear picture of the entire trial process and results, this information should not be used as a reference for any medical or financial decisions.

The statistics quoted for the Sinovac Vaccines are from ongoing studies. It is possible that the efficacy rate will change.


Biontech source data: https://investors.biontech.de/static-files/53f0968a-279b-4f82-a2fc-d67dcb6e4e91

Sinovac source data: https://chilereports.cl/en/news/2020/08/04/chile-initiates-clinical-study-for-covid-19-vaccine