The OMT thinks a curfew has a significant effect. What is that based on?

Theres gonna be a curfew. At least, if the House agrees. Many parties were previously not convinced of the effect, but today the Cabinet said: yes, a curfew is needed.

Jaap van Dissel of the RIVM said earlier that the effect of a curfew could not be predicted, but in the latest OMT opinion a numerical justification is given: the R-number, which indicates how many others infect one infected person on average, can be 8 to 13 percent by reducing it. With that, the OMT and the Cabinet sound the curfew, but where does the clapper hang?

The OMT examined four studies: two on the impact of individual measures to combat the spread of corona, from the closure of shops to a lockdown, and two studies on the situation in France.

โ€œ It always remains a bit to give a best guess,โ€ says epidemiologist Alma Tostmann at the Radboudumc. โ€œIn addition to a direct effect, a curfew can also have the added effect of emphasising the urgency to better comply with the basic measures, such as having you tested for complaints and staying at home if you are positive.โ€

Demissionary minister De Jonge explains why according to the cabinet a curfew is needed:

The

main problem is that the effect of individual measures is difficult to measure. In other countries – such as France, the United Kingdom and Belgium – a curfew has already been introduced, but always in combination with other measures. If the infections then go down, it is not really possible to disassemble how much each individual measure has contributed.

Van Dissel also recognises this: There is no country with a curfew as the only measure, he said in the technical briefing. โ€œIt remains an estimate, this is roughly the effect you expect.โ€

The studies quoted by Van Dissel also do not give an unambiguous picture. One of the studies estimates the effect of โ€œreducing individual travel movementsโ€. This intervention would reduce the R number on average by 0.08 to 0.13, but is wider than just a curfew: it is about reducing all travel movements.

Another study talks about the effect of stay-at-home orders, i.e. the obligation to stay at home. It reduces the R by 10 percent on average. But again, that is a broader measure than just a curfew.

French curfew

Two other studies looked at the experience in France with a curfew. It is clear that the number of infections is decreasing after the introduction of a curfew. But how much curfew does not contribute to that. In one of the studies, it is suggested that curfew reduces infections among those over 60. The OMT advises a curfew because it would be the most effective for 18-25-year-olds.

Curfew also has different times in France: first from 8 p.m. to 6 a.m., now even from 6 p.m. to 6 p.m. The curfew that the Netherlands wants to introduce runs from 20.30 to 04.30. In other words, the studies give a diffuse picture and the precise measure and context in which it is introduced are different than in countries that already have experience with it.

When asked, a spokesman for the RIVM says that predicting and measuring the exact effect is very difficult. On the basis of the four surveys, in which nowhere directly describes the effect of a curfew, the OMT has made its own estimate what it could โ€œleadโ€ in the Dutch situation, according to the spokesman.

โ€œ Very much depends on the characteristics of the epidemic,โ€ says Alma Tostmann. โ€œHow many infections are there, what other measures are in place, how well do people adhere to them? Everything is uncertain, the same applies to other measures.โ€

Prime Minister Rutte announced more measures than just a curfew:

It therefore seems contradictory that the OMT now provides a fairly precise estimate. In November Van Dissel gave as an example in the Chamber: โ€œWe do not have tables that say: a curfew has a 0.05 effect on the R value.โ€

At the same time, the House of Representatives bases support for the introduction of a curfew partly on the basis of the numerical justification that is now in place. The parties had asked for a calculation as concrete as possible of the effect of curfew on the R number, such as the Christian Union last week.

Reduce contacts

Before curfew, it would now be possible to โ€œput a number on itโ€, says Van Dissel in the technical briefing, where, according to him, alternatives such as a social bubble – where you can see a maximum number of people per week – cannot be extracted from literature. The only thing that is certain is that fewer contacts lead to fewer infections.

Not too much emphasis should be placed onThe exact effect of curfew, says Alma Tostmann: โ€œThe ultimate goal is to reduce peoples contacts. This can be done by curfew, but also by reducing the number of visitors a person may receive per day or per week.โ€

Or as demissionary minister De Jonge put it at the press conference: โ€œIts not mathematics and at the same time mathematics.โ€

Curfew is a spicy message, especially for people who already had few social contacts. They also notice this in organisations like Stichting Met Je Hart and De Luistenlijn: