India this week approved the Moderna vaccine, the fourth Covid-19 vaccine to be used in the country. Moderna has confirms that his shot has an effectiveness of 94 percent, higher than Covishield, Covaxin, and Sputnik V.
But if you think 94 out of 100 people who got the US-made vaccine would be protected from Covid-19 infections, you are wrong.
So what does vaccine effectiveness in general really mean? Let us understand this using the example of Moderna.
Effectiveness rate
The 94 percent effectiveness of Moderna means that if 100 people are infected with Covid-19, an average of only six would be ill if they were all vaccinated. So if a test result a. shows 94 percent effectiveness, this means that a vaccinated person is 94 percent less likely to be infected than a person without a vaccine.
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In summary, the effectiveness value shows a relative reduction in the risk of infection and no absolute probability of protection against Covid-19 despite vaccination.
The experimental math
Drug manufacturers are conducting a study with selected participants from different sections of the population who are divided into two groups: half are given the vaccine and half are given a placebo (with no active substance or a dummy vaccine).
After a certain time (nine weeks after the second dose at Moderna), researchers count how many people in these two groups have been infected with Covid-19.
By doing Moderna trial version In 28,207 of the 196 participants, for example, eleven people from the vaccination group and 185 from the placebo group were infected.
The relative effectiveness is determined by dividing the number of people infected in the vaccinated group by the placebo group and subtracting it from 1.
Here’s the simple math:
1- (11/185) x 100 = 94.1%
“The primary endpoint of the Phase 3 COVE trial was based on the analysis of confirmed and resolved COVID-19 cases, starting two weeks after the second vaccine dose. This final analysis was based on 196 cases, of which 185 cases of COVID-19 were observed in the placebo group compared to 11 cases in the Moderna COVID-19 vaccine group, giving a vaccine effectiveness of 94.1% “, said Moderna in its December statement.
According to experts, the important finding is that it is not the total number of study participants that is relevant here, but the number of people who have been infected with Covid-19.
“The Vaccine effectiveness determined in the studies are just a snapshot of the virus in the world at this time. By the time the vaccine reaches the general population, the prevalence of the virus and any variants that may be in circulation may have changed. These factors can affect the actual effectiveness of the vaccine. However, in the case of Moderna’s clinical trial data and what we’re now seeing in people of different ages, the vaccine’s effectiveness is preserved, so suffice it to say that the vaccine’s effectiveness is very similar to that seen in clinical studies. Dr. Priya Luthra, senior viral disease research and translational science program at the Trudeau Institute in New York, told India Today.
The effectiveness limitation
The Effectiveness of all vaccines is derived mathematically using the same method. The different study scenarios and the total exposure of the participants can result in different rates for different vaccines.
However, effectiveness based on clinical studies does not necessarily translate into effectiveness of vaccinations in the real world.
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