To be honest, since we live on Earth (assuming you do as well), Earth is the easiest planet to study. We don't know much about the other planets because we've never been to any of them. I believe that the second easiest planet to study is either Uranus or Saturn.
A vaccine is used to provide active acquired immunity to the host by supplying them with a biological preparation which is often made up of attenuated organism, its associated immunogenic particle, protein, DNA, etc.
Today there are vaccines available for a wide variety of diseases however there is no preventive vaccine for listeriosis.
Listeriosis is a disease caused by <em>Listeria monocytogenes</em> and it is a very serious disease often caused due to the consumption of contaminated food.
There is unavailability of a commercially available vaccine against listeriosis although a lot of research is underway to prepare a vaccine to reduce the mortality rate.
