This game was first released in Japan around 2006 or so, and Western game rags of the time dubbed it with the literal translation of "The Zombie vs. Ambulance", which made it sound a lot more fun and hilarious than it ended up being. I guess the hype led to a Europe-only localization which was instead called "Zombie Virus", a more boring name to reflect the more standard and tedious gameplay than what we were all originally expecting.
So we're in a Japanese city, there's a zombie outbreak, 90% of the residents are now dead-ified. The remaining survivors are rallying around the city hospital, conveniently located in the center of town, where a small medical staff is keeping humankind afloat. You are an EMT who wears surf shorts and Crocs for some reason, and your job is to pilot the titular The Ambulance. You'll take it out in short bursts of exploring the city, looking for survivors to pick up while mowing down zombies at high speeds.
The hospital is your hub, and you just free-roam the city at will, like GTA except you never get out of the car. You're free to return to the hospital at any time, which restores any damage to The Ambulance. Plus you'll need to come back to drop off survivors, as you can only hold two at a time at the outset (trying to pick up any more causes them to amusingly yell "Oh My Gooooooddddd!" before running off into the night).
Apparently there are more areas outside the city to unlock eventually, and even boss battles against giant worms and such. I never made it that far, because the game is just too demanding. As you're out and about, the hospital morale is constantly dropping, representing them fending off an unseen but unending zombie wave. The game's central problem is just that this morale drops *way* too damn fast. You can give it a tiny boost by racking up zombie kill combos, but the zombies spawn in sporadically and hitting a long stretch where they decide not to spawn basically nukes all your progress. Trying to hand-brake turn to wipe out a mob you've come across is so slow and clumsy that it's nearly as bad. If you can't just cruise around for a good stretch with zombies constantly spawning in front of you, you're screwed.
This one little poorly-balanced detail basically cascades out and ruins everything else. While you're trying to do donuts and kill off zombies to keep your morale up, one will inevitably latch onto the vehicle. You have to waggle the stick to shake them off, but this is iffy and seems to take forever most of the time, and a lone zombie will utterly thrash your vehicle in a very short time. You also take damage from incidental contact with anything that's not a zombie. The big issue here is that as The Ambulance takes damage it gets slower and the zombie hitting power is weaker. So it eventually hits a point where it's too beat up to kill zombies at a pace that will allow you to keep the hospital morale pumped.
This is actually a cool core concept, but it smacks of a rushjob. If the publisher had just invested a *bit* more time/money/polish this could have been a cult classic. The basic driving is solid for the most part (other than shaking off zombies), and the idea of rescued survivors appearing in your hub to serve functions like helping to hold off zombies (for military and police that are rescued) and upgrade your wheels (for mechanics) is a good one. But poorly balanced gameplay just ruins the whole thing. The game could still be salvaged if some ROM / ISO hacker could get into it and make the hospital morale decrease much more slowly ... it also seems like you could mod any mainline GTA game to do a better version of this concept if you were really ambitious.