  Electromagnetic radiation from superconducting cosmic string loops can
reionize neutral hydrogen in the universe at very early epochs, and affect the
cosmic microwave background (CMB) temperature and polarization correlation
functions at large angular scales. We constrain the string tension and current
using WMAP7 data, and compare with earlier constraints that employed CMB
spectral distortions. Over a wide range of string tensions, the current on the
string has to be less than 10^7 GeV.
