In a web site operated by A service of the U.S. National Institutes of Health, I saw a sentence like the following.

What is happened/ happening to HIV/AIDS+ Widows in Tanzania - Africa.

I can take 'what is happening' as OK with me.

But I learned that 'what is happened' is not possible, because verb 'happen' is intransitive verb.

Can you show me where I am wrong?
what is happening: OK
what is happened: not OK
what has happened: OK

Thanks, I was just wondering if my grammer that 'happen' is intransitive a verb is wrong. But you should understand my cautiousness because there are so many exceptions in any grammer.

Thanks again, Marius Hancu.