What is the difference between efficacy and effectiveness in terms of vaccines? How are these numbers calculated in trials?

The COVID-19 pandemic has taken the world by storm and, after almost two years, still has a strong presence across the globe. Not many of us will remember March 2020 or what we were doing the day the government announced a national emergency, but the aftermath is not one any of us had expected. The pandemic has changed the course of our lives and affected us physically, emotionally, and mentally. While we have developed a vaccine in record time, thanks to the unity and hard work of scientists and doctors worldwide, we seem to encounter a different variant of the virus every couple of months. Amid the chaos of the pandemic, politics and social unrest have also had a part in shaping our country. The future is uncertain as we battle the Covid-19 virus and its many variants through vaccination and social safety policies.Listed below are videos and are articles I found relevant and informative. The CDC page and the SciShow youtube page have a fast amount of info for you to look at to help answer your questions and stimulate your thinking.Videos:What You Need to Know About the Delta Variant – SciShowWhat Does a 95% Effective Vaccine Really Mean? – SciShow
Articles:CDC COVID Data Trackerhttps://covid.cdc.gov/covid-data-tracker/#datatracker-homeComparing the COVID-19 Vaccines: How Are They DifferentYale Medicine – Kathy Katellahttps://www.yalemedicine.org/news/covid-19-vaccine-comparisonWhen medical care must be rationed, should vaccination status count?The Washington Post – Daniel Wiklerhttps://www.washingtonpost.com/outlook/2021/08/23/refuse-covid-treatment-unvaccinated-triage/Questions:1: What is the difference between efficacy and effectiveness in terms of vaccines? How are these numbers calculated in trials?
2: When discussing vaccination rates and availability, the word iniquity gets thrown into the conversation. What is iniquity? Why do you think this is still an ongoing issue in 2021? How will this affect the ongoing politics of the pandemic?
3: It is still possible for someone who is fully vaccinated to experience breakthrough infections. What would be the incentive for someone to get vaccinated if we still have breakthrough infections?
4: In areas where Covid-19 is surging and vaccination rates are low, and hospitals are running out of beds and oxygen supplies. Should unvaccinated people be denied hospital or ICU beds? Is this medically ethical? (Try to also think of this from the viewpoint of health providers).
5: Variants such as Delta and Lamda are increasing in infectiousness and resistance to vaccinations despite our best efforts to fight them off. In what ways can we fix our current approach in dealing with the virus?