HIV is an enveloped virus. For the capsid protein to be presented for antibody production, the virus has to first be ingested by the antigen presenting cells. Where CD4+ T-cells and macrophages become involved in the adaptive immunity process, they end up getting infected. The best way to stop the virus is by targeting its Envelope proteins with neutralizing antibodies. These are exposed to the human immune system right from the time it enters the body and if there are sufficiently good antibodies, they can prevent an infection event altogether. For this reason, capsid is not targeted much in terms of vaccination.

Thank you so much for the answer.