There really isn't any iPhone antivirus app, but there's no need for one, either. I was the same way when I got my first iPhone, the iPhone 4, back in 2011. I thought it absolutely needed an antivirus app and I downloaded something (can't remember what the app was called). It really didn't do anything. I never installed it on any of my later iPhones.
A little background information:
Apps on iPhones, and iDevices in general, are sandboxed. This means that they don't operate outside their own infrastructure. This makes it impossible for any antivirus app to check what other apps are doing. That's the reason that there is no antivirus app in the AppStore.
In case there is some harmful stuff out in the world, Apple is known to patch this app quickly and swiftly.
I'd say, enjoy your iPhone and stop worrying, that is if you did.
I think that, if you are smart about where you go and what you download. Then there should never be a problem when it comes to viruses or malware on your device. Just stick to Apps from the Apple AppStore and don't click on random links from e-mails. If you follow those basic rules everything should be fine. Hope you enjoy your iPhone SE, its still my favourite form factor.