BERLIN—Police in Germany are investigating thousands of cases of suspected forgery of coronavirus vaccine certificates, the dpa news agency reported Wednesday. It cited figures obtained from the country’s 16 states showing more than 12,000 police investigations have been opened nationwide. Dpa reported that the number of probes surged in December, after authorities announced new restrictions that largely locked unvaccinated people out of public life. Those who supply or use fake certificates could face severe penalties, from fines and suspended prison sentences to losing their jobs. Prosecutors have opened a manslaughter investigation in one case after a woman used a fake vaccine certificate to continue working at a nursing home, despite having family members ill with COVID-19 at home. Germany’s parliament is expected to begin debating a universal vaccine mandate in the coming months, though government officials acknowledge the measure is unlikely to take effect for several months. Almost 73 percent …