updated elucidation of 'vaccination efficacy' according to Mike's comment on issue 21
updated elucidation of 'vaccination efficacy' according to Mike's comment on issue 21

ApolloDev/apollo,ApolloDev/apollo,jvd10/apollo,jvd10/apollo,jvd10/apollo,jvd10/apollo,ApolloDev/apollo,ApolloDev/apollo