Yes they only protect the thyroid and you should take them as long as you are exposed to radioactive Iodine. Which doesn’t apply to anyone living in the US.
Radioactive iodine has a very short life and breaks down within hours. By the time it blows from Japan to the US it will have broken down.
These pills ONLY prevent your body from absorbing the radioactive iodine and do nothing for any other nasties.
Feeling better already.