The problem with comparing efficacy numbers
The primary factor complicating acceptance of the Johnson & Johnson vaccine is in the top-line number: It has an efficacy level of 66%, while the other two U.S.-authorized vaccines, made by Pfizer and Moderna, have efficacy levels of at least 90%.
Trying to compare those numbers is tricky, though. Experts are quick to point out that the clinical trials were conducted at different times – Pfizer and Moderna conducted their trials before several other mutated variants had been reported, whereas Johnson & Johnson’s trials were conducted after that. Consequently, Johnson & Johnson has clinical trial data to show its vaccine can work effectively against variants first reported in the U.K., South Africa and Brazil.
In terms of preventing severe disease, hospitalization, and death, the Johnson & Johnson vaccine is comparable to the Pfizer and Moderna vaccines. With continued shortage of vaccine supply, individuals and vaccinators should take any one of the three vaccines whenever they are available so that they can get sufficient protection sooner.
Yet, the sheer difference in the top-line numbers makes it difficult to look away. According to a February 2021 Centers for Disease Control and Prevention survey, when offered the choice between a two-dose COVID-19 vaccine, either Pfizer or Moderna, and a one-dose vaccine, Johnson & Johnson’s, nearly 60% of the respondents preferred the two-dose vaccine and only 7% preferred the one-dose vaccine. Among those who preferred two-dose vaccines, 72% said they were willing to wait a month for it rather than get the one-dose vaccine now.
Such biases can have real consequences. In the European Union, 80% of the COVID-19 vaccine doses made by AstraZeneca – which also has lower reported efficacy and isn’t authorized in the U.S. – are sitting on the shelves because many people, including clinicians, believe it is inferior to the Pfizer vaccine.