While your argument has some validity, the statement said "New antibody attacks 99% of HIV strains" not "New antibody attacks 99% of HI Viri (of a given strain)

While your argument has some validity, the statement said "New antibody attacks 99% of HIV strains" not "New antibody attacks 99% of HI Viri (of a given strain)". The mutation would have to occur faster than the virus dies off.