Only around 70 percent of Germans know enough about the risk of infection from infectious aerosols.

In view of this finding and a flagging willingness to vaccinate, the German Research Foundation (DFG) published an interdisciplinary position paper on Tuesday that proposes a combination of protective measures to prevent the fourth wave.

A distinction is made between direct and indirect infections.

Heike Schmoll

Political correspondent in Berlin, responsible for “Bildungswelten”.

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Direct infection means transmission through aerosol particles when breathing, speaking, coughing and sneezing in large numbers at a short distance.

Indirect infections mean transmission through infectious aerosol particles in indoor areas that have been enriched for several hours.

Outside of closed rooms in the open, there could only be a direct infection, since indirect transmissions due to a strong dilution of the viral load are unlikely.

Risk of "super spread events"

In contrast, direct and indirect infections occur indoors. Direct infections are favored when people talk to each other for a short period of time without moving (at cash registers, hotel receptions, at the hairdresser's, in the office, at school or in a restaurant). Indirect infections take place when people stay in a room for a long time: at school, in daycare, in restaurants, offices, in shops or in local public transport, if the room is not sufficiently ventilated and air is exchanged. Infection can also take place in poorly ventilated interior rooms if an infectious person has been there for a long time.

Therefore, cluster infections or “superspreading events” could occur indoors, such as in old people's homes, dormitories, care facilities, collective accommodation, schools or elevators.

According to the position paper, on which aerosol researchers, immunologists, aerodynamicists, infectiologists, virologists and health researchers contributed, the risk of indirect infection increases even with strong breathing activity such as choir and orchestra rehearsals, heavy physical work and sports in the gym.

Masks have to fit tightly

Against the indirect risk of infection in rooms, the researchers recommend staying as short as possible. If longer dwell times are unavoidable, the air exchange must be ensured by cross ventilation, fixed or mobile ventilation systems. They must be operated with maximum volume flow and, if possible, with 100 percent outside air. But even the best room ventilation cannot provide protection against direct infections. Room air purifiers are therefore not a “substitute for masks of any kind”. The researchers therefore also recommend wearing particle-filtering masks, i.e. FFP2 (KN95, N95). They specifically point out that the mask must fit tightly.

Simple surgical masks or mouth and nose covers offer "no self-protection against indirect infections because the aerosol particles can flow in and out unhindered at the edge of the mask," says the paper. Such masks only offer a certain external protection against direct infections, because the rapid forward spread of aerosol is hindered. For all indoor gatherings - including schools and universities - the obligation to wear medical masks should therefore continue to be adhered to. In the opinion of the DFG, in order to avoid direct infections outdoors, it is important to keep a distance of at least 1.50 meters from others and to wear a mask at the bus stop, in the queue, at open-air events and demonstrations. It doesn't have to be medical, a simple surgical mask is sufficient. It is crucialthat different protective measures are sensibly combined.