DES MOINES — Iowa health officials have modified a decision they made last week to withhold COVID-19 vaccines from some counties that were reported as not having used up to 80 percent of their allocation.The Iowa Department of Public Health informed five counties last week that it would withhold this week’s allotments of vaccine because they had not inoculated enough people and needed time to catch up.The decision drew criticism from several county health administrators, who said the state was either mistaken or that bad weather had temporarily slowed their progress.