RIVM: ‘Glad that the predictions have come true, that’s good news’

Top scientific journals The Lancet and Science recently published articles claiming that aerosols, tiny droplets emitted by humans, contribute more to the spread of SARS-CoV-2 than is believed in many countries. And by extension, the importance of ventilation is also greater.

The NOS spoke about this and about the Indian variant and the development of the Dutch corona figures with Jaap van Dissel, director of the Center for Infectious Disease Control of the RIVM and Jacco Wallinga, chief modeler there.

Those studies in The Lancet and Science conclude that Dutch policy on aerosols and ventilation is also lagging behind. Some see Maurice de Hond as right.

Van Dissel: “First of all: attention to ventilation is good. At every briefing in the House of Representatives, I mention the first slide with characteristics of covid-19 ‘adequate ventilation’ with exclamation mark as an important element of its control. In confined spaces, which are poorly ventilated and where you stay with others for a longer period of time, aerosol transfers can also play a role. You can of course talk about the most important control measures. We believe that the measures, as we define them in source, collective and individual measures, with the hierarchy that we have placed in them, are and were the most important measures. They have brought the covid-19 outbreak to a halt, also in the first phase. “

So ventilation and aerosols are less important than the authors in Science and The Lancet say?

Van Dissel: “If you can isolate a source from the rest, then it is actually no longer important afterwards whether it is properly ventilated, because then there are no contagious people. The presymptomatic transmission makes it more complicated, so it can play a role. hence the collective measures such as keeping a distance of 1.5 meters. But from the point of view of dispersion in the population you have to focus on reducing the greatest risks and we have always done so. Very fine aerosols can play a role in certain situations. This can be found on the RIVM website and in the OMT letters. If there had actually been an aerogenic (via very fine aerosols, ed.) distribution, then you expect a corresponding, much higher reproduction number. spread in hospitals that you have to take measures such as negative pressure chambers and certain mouth masks. Those measures were never taken and that did not cause outbreaks. “

So those aerosols don’t play such a big role?

Van Dissel: “They can play a role in different circumstances. But from a public health point of view, of what we should do against the covid-19 outbreak, other measures are at the top. For certain situations, ventilation is very important. This is linked to behavior, because screaming or singing causes a different type of droplet formation than talking quietly, so in specific situations other types of diffusion can play a major role. CDC which has nicely summarized, the ranking in factors that determine the distribution does not actually change. Other infectious diseases that are transmitted by air and inhalation, the RS virus and the flu, for example, have also been absent in the last year. Thanks to measures against virus spread via large droplets. That is how effective these measures are against the annual respiratory viruses. “

Yet those publications about aerosols seem very solid.

Van Dissel: “You present it as if it were either one or the other. Large-scale control is all about risk reduction. Transfer depends on contact. How often is there contact, for how long and with what intensity? But context also counts: was it? outside or inside and if it was inside, was it a ventilated room or not? With many people or not? If you do not take measures, one person will infect an average of 2.5 to 3 others with this virus. By moving small drops, such as measles, that is 18 to 20 people. In the period that we did not know, we assumed that it mainly took place within those 1.5 meters and through those large drops. The measures were inoculated. They led to a direct reduction in the outbreak. In measles or chicken pox that had not worked. If covid-19 were to spread aerogen, we would have had to take much stricter measures to stop it. By the way: we have advised hospitals in situations where we know that a lot of aerosols are produced, for example during procedures such as suctioning in intensive care, to take extra measures, precisely to adequately cope with this spread via aerosols. “

But do you think a distance of 1.5 meters remains the most important protection against transmission?

Van Dissel: “Yes, after source isolation. We will soon be publishing an article about this from the RIVM. We ask very precisely how long people have contact with others, with whom and in what setting. We then held that against the presence of antibodies against the virus. in their blood. People who indicated that they adhered well to the 1.5 meters were clearly less likely to have antibodies. This is very good indirect evidence of the usefulness of the 1.5 meters and the meaning of the policy pursued against covid. 19. But that does not exclude that some situations require extra measures. “

The Indian variant is more contagious than the British one, according to the latest data from England. What does that mean for the Netherlands?

Jacco Wallinga: “We have not yet made any calculations with the Indian variant because it is still too rare in the Netherlands. We have a lot of contact with colleagues in England. The proportion of Indian variant is increasing there rapidly. If that is due to domestic distribution, then the Indian variant is clearly more contagious than the British one. But it could also be imports from India. When it comes to domestic spread, the estimate is that the Indian variant could be about 10 percent more contagious than the British one. “

Van Dissel: “In Oxford, the laboratory examined whether antibodies after an infection or vaccination also protect against the Indian variant. That looks good. According to those scientists, there is no need to worry about this.”

Finally, is the epidemic in the Netherlands now on the decline?

Wallinga: “The figures are going in the right direction, both the number of new infections and hospital and IC admissions. Just like the immunity from infections and vaccinations. It will be fine until the summer. What will happen next is uncertain. We are not sure. do not know how long the immunity lasts after an infection or vaccination. The seasonal effect that is now having a positive influence will then have a negative effect. What will further easing have the effect? ​​How will people comply with the measures that will continue to apply? We are really not going to be one, two, three free of corona. But the decline has started. Three weeks ago the reproduction number was about 1. The numbers are lower now, so is the R. That is what we predicted around Easter It is nice to see that the predictions were correct. And it is very good news. I am also delighted that the predictions have come true. “

Van Dissel: “With all the uncertainties about the further course, one thing is certain: the availability of vaccines and the willingness to vaccinate are very important. The sooner we vaccinate, the better it is. Possibly also with a third injection in the autumn, as some other countries want. to do.”

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