About 50 to 60 percent of the population of the Netherlands need to be infected by and recovered from Covid-19 for the country to achieve herd immunity against the coronavirus, Jaap van Dissel, head of public health institute RIVM said to Nieuwsuur.

On Monday evening, Prime Minister Mark Rutte said that a large part of the population will likely be infected by the virus, but that this will also build up immunity. "Those who have had the virus are usually immune afterwards," Rutte explained. "The larger the group that is immune, the smaller the chance for the virus to jump to vulnerable elderly people and other people with poor health. With group immunity you build a protective wall around them."

That is the Netherlands' strategy in the fight against this virus. But it means that more people will have to become ill. "We want to spread the virus to people who are not really affected by it," Van Dissel said. "At the same time, you try to protect vulnerable groups as well as possible. If the group that has had the virus is large enough, it will protect the vulnerable against the virus."

With the measures currently in place, the government is trying to "control the virus" as much as possible, and to level off and spread the peak of infections over a longer period. This way, immunity is built up in the population and the healthcare system is not overloaded, Dissel said.

"This is the middle scenario," Dissel said to Nieuwsuur. On the one side of this middle scenario is a scenario in which no measures are taken and the virus is allowed to spread unhindered. This would make many people sick in a short time and could overload the healthcare system.

On the other side is a "total lockdown", as was announced by other countries. But this is not the best option, according to Van Dissel. "As long as you suppress hard, there is little disease, but as soon as you stop doing that, the virus can come back right away," he said.

He referred to China, where a drastic lockdown was introduced to stop the spread of the virus. Some 80 thousand people in China have had the diseases, but that is a very small percentage of the entire population of some 1.4 billion people. "The disadvantage of such a total lockdown is that the virus will form a kind of peat fire, that there is insufficient build-up of immunity, and that you will therefore always remain sensitive to reintroduction of the virus in the future. If everything is opened up again, foci of infection can re-emerge everywhere."