It means 5-10% ineffective in stopping you from getting covid19. The death rate of the 5-10% is probably similar or less than if you had not gotten the vaccine. Death rate in US for those infected is approximately 2%. 2% of 10% = 0.2% or 200 people per 100,000. So, deaths projected per 100,000 unvaccinated is 2,000. For those vaccinated, 200. You make the call. That is your right.