AUGUSTA, Maine — Maine hospitals anticipate another surge in demand for COVID-19 vaccines after state officials announced residents aged 60 and older would be next in line for shots, an extension to a greater population than previously anticipated. Friday’s announcement that Maine would switch to an age-based vaccination system comes as three out of five Mainers aged 70 and up have received at least one vaccine dose while the state’s vaccine allocation is expected to increase and the one-dose Johnson & Johnson vaccine is likely to be approved by the federal government this weekend. Appointments have been easier to come by for many Maine seniors over the past few weeks as supply has increased.