Bharat Biotech on Tuesday said it has collaborated with the Netherlands-based Bilthoven Biologicals B.V, a wholly-owned arm of Serum Institute of India, to strengthen production and supply security of oral polio vaccines. An agreement has been signed between the two partners under which Bharat Biotech will procure drug substances for the production of oral polio vaccines (OPVs) to be supplied within India and globally, the company said in a statement.