An April 2021 in The New England Journal of Medicine details the results of a randomized clinical trial designed to evaluate the efficacy of a single dose of the Ad26.COV2.S vaccine (Johnsons and Johnson) for preventing Covid-19 infections. As per the authors:

"In an international, randomized, double-blind, placebo-controlled, phase 3 trial, we randomly assigned adult participants in a 1:1 ratio to receive a single dose of Ad26.COV2.S (51010 viral particles) or placebo. The primary end points were vaccine efficacy against moderate to severe-critical coronavirus disease 2019 (Covid-19) "

The following Kaplan-Meier curves show cumulative incidence of Covid-19 (moderate to severe) in the Ad26.COV2.S (vaccine) and placebo groups over the 4-month follow-up period.

https://docs.google.com/spreadsheets/d/1c9v3xgMHaIU106iE7zdupq2jDI_iw8jMGNCS70_90Xk/edit?usp=sharing

The incidence rate ratio and 95% confidence interval), of contracting Covid-19 for the vaccine group compared to the placebo group is 0.33 (0.27, 0.41). Please note, for the following questions IRR is the abbreviation for "Incidence Rate Ratio".

Question: Is the association between Covid-19 infection and the Ad26.COV2.S vaccine statistically significant?

a. Yes, because the 95% confidence interval for the IRR does not include 0.

b. No, because the 95% confidence interval for the IRR does not include 0.

c. Yes, because the 95% confidence interval for the IRR does not include 1.

d. No, because the 95% confidence interval for the IRR does not include 1.