In early march more than 6000 doses of the Johnson & Johnson vaccine were supposed to be shipped to Detroit, Michigan, however their mayor, Mike Duggan, said no to the shipment stating “Moderna and Pfizer are the best, and I am going to make sure that the residents of the city of Detroit get the best,” in reference to the 94-95% efficacy rates of Pfizer and Moderna in comparison to Johnson & Johnson’s 66%.
Mayor Duggan’s major mistake was assuming that efficacy rates mean that the vaccine is ‘better’ than another. Realistically, efficacy rates are the least important in determining vaccine quality. By looking at how efficacy is determined you can find out why.
More than 40,000 participants were involved in the trials for the Pfizer vaccine, these participants were separated into groups: those who received the vaccine and those who received the placebo. After being inoculated, these participants were sent out to continue their everyday lifestyles and monitored by scientists to see if they become sick with COVID-19. At the end of the trials, 170 people contracted COVID-19. The determining factor of efficacy is decided based on how these people fall into each category of placebo and vaccine.
An even split among those with COVID-19 who received the vaccine versus those who did not would indicate a seemingly useless vaccine, as it would be just as likely that you became sick whether or not you were vaccinated thus a 0% efficacy. Alternatively, if all 170 people who got the vaccine were in the placebo group, this would mean the vaccine has 100% efficacy. For the Pfizer vaccine specifically, 162 people out of the 170 were from the placebo group, while the other 8 who contracted COVID-19 were in the vaccinated group, garnering a 95% efficacy.
In a group of 100 people this does not mean that in turn 5 people would get sick, instead this number is applied to the individual and means that each individual who got the vaccine would be 95% LESS LIKELY to get COVID-19 for each encounter they have with the coronavirus.
So, if each vaccine’s efficacy rate is calculated the same way, what does the variance in efficacy mean?
As a first look, the circumstances of each vaccine trial are different, including where in the COVID-19 pandemic timeline it was done. When the Pfizer and Moderna trials were done, around August to November 2020, the exposure rate due to daily cases of COVID-19 were significantly lower than what it was during the Johnson & Johnson trials, which were held from October 2020 to February 2021. The Johnson & Johnson time period was right when surge cases were rising significantly, causing participants in the study to have more opportunities to be exposed to COVID-19 and at a much more frequent rate than the participants in the Pfizer or Moderna vaccine trials were.
The location of the trials also should be taken into account: Pfizer and Moderna were both done in the United States, while Johnson & Johnson’s study was primarily in South Africa and Brazil. Case rates were not only higher in these countries, but they were also dealing with a different strain of the coronavirus altogether.
With this in mind, it is mostly misguided to judge these vaccines with one another because the circumstances are vastly different so they cannot be scrutinized under the same lens unless their studies met the same criteria. It would not be unlikely to see a similar efficacy rate with Pfizer or Moderna, if their studies were done at the same time and place as Johnson & Johnson. Amongst all vaccine trials, not one single person had to be hospitalized or died if they received a vaccinate, however the same cannot be said for the placebo groups.
Most important of all, the goal of these vaccinations is to prevent infection and reduce the severity of sickness or death if the virus is contracted, not make the likelihood of getting COVID-19 absolutely zero.
