Since March 16th, the Netherlands has pursued a mitigation strategy that allows the virus to spread in a controlled fashion. Gradually obtaining 'herd immunity' has been a central part of the strategy, at least of its messaging, since mid-March.

Even though herd immunity as a concept has subsequently been de-emphasized, it continues to be an important consideration for the Dutch government and its scientific advisors, as evidenced below. Therefore, this article aims to give an exhaustive overview of the role the concept of 'herd immunity' has played and continues to play in the Dutch coronavirus strategy.

Herd immunity is a usually achieved by vaccination programs, when a large enough percentage of a population has become immune due to vaccines being administered, to the extent that a virus is unable to reproduce. It can conceivably be achieved organically through infections, but this not a known practice – and therefore a highly controversial idea – for human populations, as it will only protect the minority of people that will not at some point in time get infected. The concept of 'overshoot' makes this 'protected' part minuscule. And It's impossible to 'shield' the vulnerable in this process, because there are too many people that would count as vulnerable and it's impossible to rule out risks – especially the risks from human closeness – since many vulnerable people need hands on care. For coronaviruses including COVID-19, the concept of herd immunity is especially controversial, because there is no conclusive evidence on the extent of immunity gained and the duration the supposed immunity will last. Coronaviruses are known to not give lasting immunity and even the RIVM says that it's suspected that severe infections offer the best immunity afterwards. At that point the damage is already done of course, as those people are the ones that often have longterm health damage.

Officially, The Netherlands pursued a 'containment' approach prior to March 12th, as is detailed in our exhaustive Timeline article.

•March 13th: Jaap van Dissel says '50% of the people in the Netherlands may become infected' and: 'The virus will stay with us, we will have to go through this as a society'.

•On March 16th: the Imperial College of the United Kingdom publishes its report which introduces a sharp change in direction for the UK's general strategy. As The Guardian writes:

Herd immunity is normally created by vaccinating large numbers of children, safeguarding those who cannot be inoculated. Nobody has ever tried to do that by allowing infection with a disease before – and now, it appears to have been recognised that it’s not safe to try.
The Guardian (March 16th)

•March 16th: television address by PM Mark Rutte, explaining the mitigation strategy (named ‘maximum control’) focused on the controlled buildup of herd immunity.Translation here.

•March 18th: Mark Rutte clarifies 'herd immunity is not the goal, but an effect' - although it is unclear what the difference really is. Jaap van Dissel, the head of the Outbreak Management Team said the same that day. See below.

•April 16th: only 3% of the Dutch have coronavirus antibodies, as evidenced by a Sanquin study, which is considered to be a major blow to any aspirations RIVM and the government my have regarding the controlled buildup of herd immunity.

•April 18th: no proof of immunity in recovered coronavirus patients, say WHO (Irish Times).

•April 19th: in an interview with Dutch broadcaster NOS, Jaap van Dissel and Jacob Wallinga defend the strategy of building herd immunity. Van Dissel says any percentage of people being immune will be 'an invisible wall the virus will bounce off of'. Wallinga adds: "Every immune person counts. But before it is really useful it, it has to rise to 60 percent. I imagine we are hoping for a vaccine or a therapy. But if that doesn't work, by then we'll be well on our way to that 60 percent."

•April 21th: Dutch OMT member Ann Vossen appears on Dutch tv show Jinek and explains that the strategy is to allow the virus to spread slowly, including on children day care centres and primary schools.

April 24th: The NVIC (national association for intensive care) publishes a report with calculations of the needed ICU beds and time to reach herd immunity levels (50-70% infected).

•April 28th: SAGE member John Edmunds is grilled on Channel 4 about the initial 'herd immunity' strategy being a mistake.

•May 4th: Is our 'intelligent lockdown' really that intelligent? Nieuwsuur reports on our strategy, including the 'herd immunity' concept that keeps raising its head.

•May 6th: Rutte states in the press conference that herd immunity is not a goal but a side-effect and that that is the strategy 'everywhere', naming some examples: France, Germany, Denmark, Belgium, Spain, Italy. This is not turetrue.

•May 7th: The concept of 'herd immunity' has really disappeared from the Outbreak Management Team talks, says OMT member Marc Bonten.

•May 11th: WHO's Mike Ryan speaks out against herd immunity.

•May 18th: GGD director Sjaak de Gouw says that trying to build herd immunity is the only option that you can do and portrays containment as a strategy that would cause travel restrictions for Dutch people that want to go abroad. Original video. Tweet with subtitled video.

•May 20th: In the technical briefing to parliament members, Van Dissel shows a graph portraying the buildup of herd immunity by infection. He also shows a map with the % of blood donors that have antibodies (3% on average, April 16th), that supposedly indicates immunity. (Tweet) He does say that he doesn't expect The Netherlands to reach full herd immunity by infection, the hope is for a vaccine to complement the natural herd immunity.

Slide from van Dissel's presentation, showing recurrent (semi-)lockdowns and the result of an antibody study

•May 25th: OMT member and doctor-microbiologist Marc Bonten seems to try to downplay the role of herd immunity in the strategy. He says the acquired herd immunity will likely just be partial, because it takes a lot of time to build it within the limits of ICU capacity and hopefully there will be a vaccine. 'And if not...then it will take a long time before herd immunity will deliver us from the 'new normal''. He also emphasizes that even immunity of for example 20% of the population can allow for more relaxations of measures.

•Dr. Devi Sridhar on herd immunity. See original tweet.

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