(Adds pandemic context, comment from export industry chamber) BUENOS AIRES, May 20 (Reuters) - Argentina’s grains exports remained paralyzed on Thursday due to a strike by port workers demanding to be vaccinated against COVID-19, with the labor groups threatening another 48-hour work stoppage next week. Argentina’s Port and Maritime Activities chamber told Reuters the strike on Wednesday and Thursday had halted port activity. Industry leaders agree port workers should be protected from COVID-19, but Argentina’s vaccination program has had a slow roll-out. After a meeting with government officials late on Wednesday, the unions issued a statement saying they would “continue the struggle to protect our health and are ready to call a new 48-hour strike starting at 00:00 hours on Wednesday May 26.”