Why only one dose?
The recommendation that only one dose be given - which the CMOs said could be looked at again in the spring - is related to the very rare risk of a condition called myocarditis, or inflammation of the heart muscle.
It can cause chest pain and heart palpitations, but cases are usually mild and children recover quickly with standard treatment.
The risk is tiny after one vaccine dose and slightly higher after two, with 12 to 34 cases seen for every one million second doses.
Boys are at higher risk than girls.
And most of the benefits from the vaccine, which reduce the small risk of illness, are gained after one.