18 Nov

Pfizer-Biontech and Moderna recently announced the first interim efficacy analysis of their Covid-19 vaccines. The financial markets cheered the news as an early marker of success. Divya Rajagopal explains what the trial landmark means

First interim vaccine efficacy results 

1. Pfizer-Biontech-bOver 90% 

2. Moderna- 94.5% 

Stastically, there’s not much difference between 90% and 94.5% efficacy since they lie in a range 

What is vaccine efficacy?

It’s the degree by which the infection is reduced in a vaccinated group compared with an unvaccinated one

Essentially, it measures disease prevention by the vaccine among trial participants

It’s based on a randomised 1:1 trial of the vaccine and placebo groups Moderna example 

  • 30,000 participants in trial in US
  • First analysis based on 95 confirmed cases of Covid-19
  • 90 cases in placebo group
  • 5 cases in vaccine group
  • This yielded an efficacy rate of 94.5%


  • This early data shows very good results
  • The US FDA benchmark is an efficacy of above 50%

 Efficacy Vs Effectiveness 

  • Efficacy of a vaccine indicates its success in a randomised, controlled trial
  • Effectiveness measures how the vaccine works in a real-world setting
  • Real-world effectiveness is usually less than in a controlled setting
  • It takes many years for science to determine what an effective vaccine is
  • That’s why vaccine trials run for several years

Is this data enough? This is indeed a positive development, says Gagandeep Kang, leading vaccine expert. However, the next set of data to watch out for will be whether these numbers hold up after 52 days of dosage, the effectiveness on immunocompromised people, the elderly and children. 

Source : Economic Times

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