What does it mean for the COVID-19 vaccine to be 95% effective?

As countries around the world prepare for mass campaigns against coronavirus vaccines, drug manufacturers called out percentages in the 1990s in terms of the effectiveness they believe will be shot. But does that really mean that nine out of 10 people who get stabbed won’t get COVID-19?

Two vaccine manufacturers said preliminary results from their late-stage studies suggest that their experimental vaccines are strongly protective. Moderna said last week that her vaccine appears to be almost 95% effective. Oxford / AstraZeneca also said its vaccine was over 70% more effective, but that number could rise to 90%. This followed the announcement by Pfizer and BioNTech that his footage seemed similarly effective.

Those percentages have raised hopes around the world that vaccines could help stop a pandemic sometime next year if they continue to show that they prevent disease and are safe. But what do the numbers actually mean?

The term “vaccine efficacy” is what scientists use to denote a reduction in the incidence of disease among a vaccinated group compared to an unvaccinated group under optimal conditions, according to Dr. Shelly McNeil of the Canadian Center for Vaccinology. Efficacy is determined by clinical trials and hence the figure of 95% for some coronavirus vaccines.

However, the effectiveness of the vaccine refers to the drug’s ability to prevent diseases in the “real world”, McNeil explained in a presentation published by the World Health Organization (WHO).

Although it is possible that efficacy and efficacy are the same, for most vaccines the efficacy is lower in practice than in clinical trials. Inhibition factors in the general population, such as chronic health problems, may reduce the effectiveness of the vaccine.

In short, broad, early efficiency figures don’t tell the whole story. Scientists also need to understand how well the vaccine protects people in different age groups and demographic categories.

For both vaccines, the provisional results were based on people who had COVID-19 symptoms that triggered a virus test. This means that we do not yet know whether someone who has been vaccinated can still become infected – even if they do not show symptoms – and spread the virus.

It is also unknown whether the recordings will provide permanent protection or that amplifiers will be needed. For example, the Pfizer vaccine requires an enhancer 21 days after the initial dose.

Efficacy numbers will vary as vaccine studies continue as early calculations were based on less than 100 cases of COVID-19 in each study. There were concerns that coronavirus vaccines could be just as effective as influenza vaccines, which have ranged from 20% to 60% in recent years.

However, early results give strong signals that vaccines could prevent most diseases when large groups of people are vaccinated.