How do COVID-19 vaccines compare with other existing vaccines?

The novelty of the COVID-19 vaccines may seem daunting for some, and it is natural for questions to arise on their effectiveness. In this feature, we examine the difference between effectiveness and efficacy, compare the COVID-19 frontrunner vaccines to other vaccines, such as the flu shot, and compare their safety considerations.

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As Pfizer/BioNTech roll out their COVID-19 vaccine throughout the United Kingdom and the United States, the world wonders how effective it will be.

Looking at the three leading vaccines that we have previously reported on, Pfizer/BioNTech boasts 95% efficacy, the Oxford/AstraZeneca vaccine candidate has an average of 70% efficacy, while the Moderna vaccine candidate reportedly has 94.1% efficacy.

Effectiveness vs. efficacy — what is the difference?

Firstly, it is worth noting that “effectiveness” and “efficacy” are not the same. Despite news outlets frequently using them interchangeably, efficacy refers to how a vaccine performs under ideal lab conditions, such as those in a clinical trial. In contrast, effectiveness refers to how it performs in the real world.

In other words, in a clinical trial, a 90% efficacy means that there are 90% fewer cases of disease in the group receiving the vaccine compared with the placebo group.

However, the participants chosen for a clinical trial tend to be healthier and younger than those in the general population, and they generally have no underlying conditions. Furthermore, researchers do not normally include certain groups in these studies, such as children or pregnant people.

So, while a vaccine can prevent disease in a trial, we might see this effectiveness drop when administered to the wider population.

However, that is not in itself a bad thing.

Pfizer study shows vaccine effective against new variant

Scientists recently identified two new strains of SARS-CoV-2 — one of which had been discovered in the United Kingdom and the other in South Africa. A new Pfizer study concludes that its vaccine should be effective against the U.K. variant.

Both new variants, which appear to be more contagious, have mutations in a spike protein called N501Y. 

Because most vaccines currently under investigation essentially teach the immune system to respond to the spike proteins, some people have questioned whether the vaccines will be effective against the variants. 

The new study, which appears on a preprint server, is a combined effort from Pfizer and scientists at the University of Texas Medical Branch at Galveston.

The researchers analyzed blood samples from 20 people who had received the Pfizer–BioNTech vaccine during previous clinical trials. 

They demonstrated that antibodies from vaccine recipients successfully fought off a virus with the N501Y mutation. The study has limitations, though. For instance, the variant first identified in South Africa has an additional mutation known as E484K, which the new study did not address. 

Importantly, the study has also not yet been peer-reviewed. Meanwhile, Pfizer’s chief scientific officer, Dr. Philip Dormitzer, acknowledges:

“It was a very reassuring finding that at least this mutation, which was one of the ones people are most concerned about, does not seem to be a problem.”

The authors of the preprint conclude: “The ongoing evolution of SARS-CoV-2 necessitates continuous monitoring of the significance of changes for vaccine coverage. This surveillance is accompanied by preparations for the possibility that a future mutation in SARS-CoV-2 might necessitate a vaccine strain change. Such a vaccine update would be facilitated by the flexibility of mRNA-based vaccine technology.”