Normal flu mortality rates are about 0.1% and are generally of young (under 2) or elderly (aged over 70) people, and occur mainly during the winter.
The last major H1N1 pandemic (1918-1919) had a mortality rate of 10-20%, mainly among healthy young adults, and occurred throughout the year. 30-40% of the worlds population may have been infected.
Records show that there were 3 waves, approximately 4-6 months apart. There were relatively few casualties among the first wave in March. However, the virus mutated to a much more deadly form for the second wave in August, with 5x more casualties. The virus mutated again to a more mild form for the final wave in the following February, although it still had 2x the casualties than the first wave.
Populations with a high level of mobility were among the first and hardest hit, so the measures being taken by Governments and the WHO would seem to be sensible.