MARSHFIELD — Marshfield's mass vaccination site at the fairgrounds will open on Monday to all Plymouth County residents and those eligible for the vaccine can start signing up through the state's website at 2 p.m. on Saturday. The vaccination center at the fairgrounds has a maximum capacity of 600 doses administered per day but the state has only given the town that many doses for all of next week. Town Administrator Michael Maresco said there is a shortage of vaccines in the state, and across the country. The town will learn each successive Sunday how many doses will be available for the following week. That will dictate how many appointment slots will be set for each day and how far spread apart they will be.