Thousands of dogs across Britain are dying or suffering severe allergic reactions after being treated with a vaccine meant to protect them against mild bacterial infections. Fears over the safety of the vaccine against leptospirosis - a bacterial infection spread to dogs through rats and wild animals - have now led veterinary organisations to issue warnings about its side effects. The World Small Animal Veterinary Association (WSAVA) is urging owners not to use Nobivac L4 vaccine on puppies under 12 weeks old. However, [it] is still being administered in veterinary practices across Britain to dogs from seven weeks old, with little warning of the potential side effects. According to reports made to the Government's Veterinary Medicines Directorate (VMD) by pet owners, more than 120 dogs are feared to have died after receiving a dosage in the three years the product has been on the market. In the last two years, regulators have received 2,000 reports of dogs having suspected adverse or fatal reactions. Owners that have opted for the L4 vaccine ... have reported adverse effects including epileptic fits, swollen glands and blindness. The vaccine, which is manufactured by MSD Animal Health, a subsidiary of American conglomerate Merck Sharp & Dohme, is currently being monitored by the VMD. The regulator has however refused to reveal the total number of animals that had been affected since the product came onto the market, prompting concern among dog owners that the scale of problem is being kept hidden from the public.