So why doesn’t it?
Here’s a thought-experiment. What if the results of Johnson & Johnson Phase 3 clinical trial of the company’s one-shot adenovirus-vector vaccine finds in January that it is safe and, say,90 percent effective at preventing COVID-19 infections? Surely, the regulators at the Food and Drug Administration (FDA) would issue an Emergency Use Authorization (EUA) for that vaccine. After all, the agency in June set the efficacy threshold for a COVID-19 vaccine that it would prevent disease or decrease its severity in at least 50 percent of people who are vaccinated. For comparison, the latest pneumonia vaccines protects 50 to 85 percent of relatively healthy adult recipients against invasive pneumococcal disease. With respect to seasonal influenza vaccinations, the Centers for Disease Control and Prevention notes that vaccine effectiveness has generally ranged between 40 percent to 60 percent. «This means that people who get vaccinated may still get sick, but they are about half as likely to get sick as someone who was not vaccinated,» observes the agency. «Another important thing to remember is that vaccination may make illness less severe in people who get vaccinated and still get sick.
