True. Some vaccines are more effective than others, due to a variety of factors, including how quickly the virus/bacteria replicates or mutates, and how it spreads. With flu vaccines it is partly which variants are in the vaccine and if they match to active ones that season. One's age is an issue as well. I had measles as a kid and was almost 70 when I got measles vaccines, because one's immunity wanes through the years and isn't as strong as well you are young. Regarding the covid vaccines, all use the covid spike proteins to trigger the immune system. If someone has a compromised immune system, they aren't going to be as effective. Here is more info: https://www.yalemedicine.org/news/covid-19-vaccine-comparison