"The number of infections is increasing, as well as the number of deaths from Covid and especially the number of patients in intensive care units in some regions of Germany, regions where vaccination rates are not as high as in other regions," Spahn said Wednesday, adding that the speed of administration of the booster shots "is not sufficient."
So far only 66.8% of the population are fully vaccinated in the country. Vaccination has been slower in the Eastern states of Saxony and Thuringia, where vaccination rates are at 59% and 62.2% respectively, according to Ministry of Health figures.
"The truth is that there would be far fewer Covid-19 patients in [intensive care] if everyone who could do it got a vaccination," Spahn said.
He also called to strengthen checks at public venues where only those with proof of vaccination or a Covid-19 recovery certificate will be granted entry.
"This has nothing to do with harassment to vaccinate, it is mainly about avoiding overloading the health system, as we see in Saxony and Thuringia," he said.
Lothar Wieler, president of the Robert Koch Institute (RKI) -- the German federal government agency for disease control and prevention -- told the same press conference, "If we don't act now, this fourth wave will still bring a lot of suffering. Many people will become seriously ill and die, and the health care system will be heavily burdened."
The German Hospital Association (DKG) also warned Wednesday of Covid-19 releated staff shortages.
According to a DKG poll, 72% of hospitals said they had less staff in intensive care on hand than at the end of 2020. And 86% of those hospitals said they cannot operate their intensive care wards fully because of staff shortages,
Reasons for that shortage are, according to the DKG, staff resignations and shorter working hours due to the pressures of the pandemic.
On Wednesday, the state of Baden-Wurttemberg imposed new Covid-10 restrictions after more than 250 intensive care beds were filled up for two consecutive days. Residents will now need to present a negative Covid-19 test no older than 48 hours to enter restaurants and cinemas.
German Chancellor Angela Merkel is "very worried" about decreasing hospital capacity, according to German government spokesman Steffen Seibert at another press conference on Wednesday.
"What worries her just as much is that we continue to have more than 16 million unvaccinated adults in Germany, more than 3 million unvaccinated over the age of 60," he said.
"The pandemic is not, like some in the summer may have imagined, on the decrease, but it is challenging us now and will do so greatly in the coming weeks," Seibert added.
Despite the widescale availability of vaccines this winter compared to the last, Europe is the only part of the world reporting an increase in new Covid-19 cases globally, the World Health Organization (WHO) said last week.
The suffering has been acute in Eastern Europe and Russia, which are battling mounting deaths and cases fueled by vaccine hesitancy that has seen coverage rates dip as low as 24%, according to data from the European Centre for Disease Prevention and Control (ECDC).
Differing vaccination rates have put Europe's East and West on two separate tracks, but they share rising case rates driven by the relaxation of pandemic restrictions as economies open, cold weather driving people indoors, and the highly transmissible Delta variant, say experts.