Vaccinations are being carried out at the Meyer Turku shipyard in Finland after an outbreak of pneumococcal pneumonia.
The yard has reported 21 cases of the serious infection in late summer and early autumn. The country as a whole experiences only 300 to 350 new cases each year among the working-age population.
Meyer Turku said in a statement that the group worked on finishing new vessels.
"The group of patients includes people of different professions and nationalities and employees of different companies," it added.
"Common to all of them has been that they have worked for long periods of time in a ship under the final stages of construction."
The situation is being investigated jointly by health authorities and the city of Turku.
Measures to improve hand hygiene will be taken, the shipyard added.
"Pneumococcal infections at the site may be prevented through vaccination and meticulous hygiene," it added.
The yard is building seven large cruiseships for Royal Caribbean, Carnival and TUI.
The first one due is Carnival's 181,000-gt Costa Smeralda next month.
The Finnish institute for health and welfare said the pneumococcus bacteria is spread through respiratory droplets and by direct contact.
It said it was unlikely to have been spread through touching ship surfaces.
"The bacteria may survive on surfaces for short periods, but this is highly unlikely to be the source of transmission," it added.
Risk low
There are around 6,000 people working at the shipyard and the risk of contracting the disease is very low, the institute added.
The vaccine has been recommended for those working regularly and full time in the final the stages of outfitting a vessel there.
Other outbreaks among shipyard workers have been described in Northern Ireland in 2015 and in Norway earlier this year.
