[This item is identical to that on maurice.nl, if you follow both blogs]
On 26 November, a major experiment took place at Schiphol. Through a good analysis, it can teach us a lot about the mistakes made in the interpretation of PCR tests and also that reinfections with Covid-19 are (strongly?) overestimated.
The information from this article, by Maurice de Hond (maurice.nl) and Anton Theunissen, comes from contacts with passengers and public sources.
Detained in plane for five hours
On November 26, around 11 o'clock in the morning, two planes from South Africa arrived at Schiphol. One from Cape Town and the other from Johannesburg. There were more than 600 passengers on both flights. Along the way, panic had broken out in Europe about the Omicron variant in South Africa and they wanted to test all the passengers after arrival.
First, the passengers were kept in the plane for about 5 hours and then they were transported by buses to two separate rooms in Schiphol (on the G and E piers). Between 4 p.m. and 8 p.m., the passengers were tested by the GGD (PCR). People were waiting in a long queue and a small number of testers carried out the tests.Among others, a journalist from the New York Times, who was one of the passengers, described both in tweets and afterwards how great the chaos was and how little was done both on the plane and in the shelter to prevent people from infecting each other.
The first results came in around midnight. In the end, 61 of the passengers (10%) were found to have tested positive by GGD-Kennemerland and 18 of them were diagnosed with the Omicron variant.
The vaccinated passengers did not need to be tested prior to the flight. The unvaccinated did have to present a negative test (PCR or antigen). The majority of the passengers were vaccinated.It was like a 3G event.
Information appeared in the media that 90% of those who tested positive had been vaccinated.
The number of 61 people who tested positive is unbelievably high. Suppose that the incidence on November 25 in South Africa at that time was 2% (which is a very high estimate) and that 75% of the passengers were vaccinated, then a result of 10 people tested positive after arrival, plus or minus 3, would be the most likely outcome.
So how could it be that there were about 50 more?
A few days later I tested negative again
We know the sequel of 49 passengers out of 61 who tested positive on 26 November:
- 24 passengers tested negative on December 1 and were allowed to leave the quarantine hotel. 20 tested positive at the time.
- A Portuguese passenger had a negative PCR test when departing from South Africa. She tested positive at Schiphol. A day later, she had tested negative via a rapid test. And two days later at a hospital in Groningen there was a negative PCR test and she was allowed to go home.
- A Dutch passenger had tested positive at Schiphol. Four days later, she and her two travel companions tested negative at the GGD.
- Three passengers had a rapid test negative shortly after that Friday.
Of the remaining 12 who were not in the quarantine hotel, the sequel is not known to us.
How could 61 passengers have had a positive PCR test?
As indicated, it is extremely unlikely that 61 (almost 10%) passengers were infected at that time when they departed from South Africa. The incidence in South Africa was far too low for that. (For example, the Netherlands now has an incidence of 2%).
But how can 61 positive PCR results have been recorded on September 26 (and 18 Omicrons)? And shortly after those positive results, a majority are no longer positive (29 of the 49 of which a result is known)?
The following seems to be a very plausible explanation and teaches us more about the value of the PCR test and about our immune system:
This information is important in this regard:
1. Multiplication of the sample
The PCR test in the Netherlands uses high CT values (up to 45). The CT value (Cycle-Treshold) is the number of times that the sample – which was taken from the passenger – has been multiplied in order to be able to examine it for the possible presence of the virus. The lower the value when the virus has been found, the more virus particles were present in the original sample. Realize that a CT value of 30 means that the original sample has been multiplied by a factor of 1 million or more.Here is a Dutch explanation of working with the CT values.
There is a lot of discussion about those CT values.On August 29, 2020, there was an extensive article about this in the New York Times. Various experts indicate that values above 35 actually say nothing about whether the person in question is really infected at that moment, let alone contagious to others. Because virtually no virus has been found. For example, the article indicates that at a test laboratory in New York, 43% of those who tested positive were not positive after 40 cycles at 35 cycles.
And this is the development ofthe CT value of a number of patients, who received a PCR test several times. It is easy to see that over time the CT value has to become higher and higher in order to be able to find the virus.
Other studies showed that tested individuals with symptoms had a CT value that is typically below 30.
2. Viral doses
In whether or not you get infected, the viral doses play a big role.From this research by Prof. Streeck at a carnival gathering in Gangelt in February 2020it is clear that the longer one was present in that room, the greater the chance that one had become infected, but also the more symptoms one had. Young people apparently had a higher threshold value than older people.
But this also means that other people who were present in that room received viral doses that were too low to eventually be infected by it (for whatever reason). Everyone who was present at that Carnival gathering must therefore have been exposed to floating virus particles and inhaled them!
Oneplausible explanation
PCR tests are known to have a chance that you will test positive for weeks after an infection. There may still be "old virus particles" in the nose or throat, which are then detected. In Madrid, an overview was made of the CT values determined in relation to the development of the number of positive tests. This concerns the period July 2020 to March 2021. In yellow you will find the number of positive tests per day. In blue, the percentage of PCR tests with a CT value above 30. The increase in that percentage is clearly visible when the wave has passed its peak. And a drop in that percentage if a wave forms.
In the Netherlands, the PCR test is therefore performed with CT values above 40. So the chance that people with very few virus particles will come out of the test as positive is then a lot greater, as shown by the article in the New York Times and by this graph in Madrid. Because the yellow bars would have been a lot lower if they had stopped at a CT value of 30 in Madrid.
Is the high percentage of passengers with a positive result due to "old" virus particles that have still been found? But how can it be that their second tests, shortly after the one at Schiphol, have already yielded such a large number of negative PCR tests?
The explanation we have for it is:
Most of the virus particles found in the PCR test at Schiphol were not the virus particles produced by the passenger himself, but the virus particles inhaled by that passenger, which were still present in the nose or throat
This was done in the following way:
Before the PCR test was performed, the passengers had been on a waiting plane for about 5 hours (after an 11-hour flight). Then briefly in a bus and then stood in line for a while before being tested (depending on when it was their turn).
If our calculations are correct, then a total of between 7 and 13 people could have been present on the two flights, who were infected prior to the flight and may have been able to introduce virus particles into the air (aerosols). In those 5 hours on the ground in the plane (and perhaps in the bus and then in the reception area) it is almost inevitable that the other people present have inhaled the airborne virus particles. Even if they had overwritten the viral doses to really be infected by it, they could only be someone who spread virus particles that had been produced in their own body 2.5 days later.
It seems very likely that a large number of those present inhaled a limited number of virus particles in the time between landing and the execution of the test. But most do not need to have exceeded viral doses to eventually become infected.
And there we come to the core:
Because the PCR tests are very sensitive, even a small number of virus particles in the passenger's nose or throat may have resulted in a positive result.
As we know, the presence of the virus does not immediately mean that an infection is taking place. Because the moment of testing took place immediately after an infectious situation, the test was too early to say anything about infection or infectiousness.The PCR test simply detected that virus particles had been ingested.
The fact that people then test negative a few days after the positive PCR test at Schiphol supports the assumption that this must have been the case for many of those 61 and that the immune system was able to remove a limited dose of the virus almost immediately or at least within a few days, without infection. And so, a few days later, no more virus particles were found and the passenger in question had not become infected and had become a producer of virus particles.
Among the 61 people who tested positive, it is estimated that there were about 10 who produced the virus themselves and had therefore "rightly" received a positive test and the rest did have virus particles in their nose or throat. That virus was not multiplied by the carrier himself but came from outside!
Of the 26 passengers who received a negative PCR test between November 29 and December 1, the vast majority, if not all, will have been in the group that had not "produced" the virus themselves.
If the CT value could be announced for each test carried out at Schiphol and for each passenger in the following week, our description of this possible course of events could be fully substantiated. Passengers who arrived at Schiphol on Friday with a CT value of less than 30 are those who were the producers of the virus (a lot of virus) and those with a CT value of more than 35 the recipients of the virus.
If one wants to assess the status of the 20 people who received a positive test in the hotel on December 1, it is informative to compare the CT value of December 1 with that of November 26. Because it could be that some out of 26ehave ingested such viral doses that they really became infected. But the virus found had not yet been produced by that person. About three days later, this should lead to the self-production of the virus and thus a much lower CT value.
So among those 20, who had not tested negative a week after arrival, there may have been passengers who had a high CT value on November 26 and a clearly lower one on December 1. So they are on the 26einfected.
And those who had a high CT value on November 26 and a lower one on December 1? These were the people who had already been infected in South Africa and transmitted the virus to the other passengers. Or they are people who, for one reason or another, have ingested more virus (talked a lot with a contagious neighbor on the plane) but nevertheless seem to have successfully fought the virus.
Perhaps this information, combined with the location of the passengers on the plane, could provide even more interesting additional information. In any case, we know of two people who had sat next to each other on the Cape Town plane and were both tested positively at Schiphol that they had no symptoms at all and one had a negative rapid test on Monday and the other a negative PCR test on Friday.
By analyzing at least the CT values of all tests from the PCR tests of Friday 26 November and the new tests in the following days, a good picture can be given of what may have happened.
The major consequences of this finding
The above also shows that a positive PCR test can be explained in many ways. And that it is very important to disclose the CT value per test! Both for those involved and for the analysis of how the spread of the virus is going.
But perhaps even more important is the next consequence of testing positive with inhaled virus particles, without having become/will become infected.
Someone is wrongly classified as someone who has had the Covid-19 infection. And if such a person is "really" tested positive much later, it is considered a reinfection, while in reality it is only the first infection.
PCR tests with high CT values therefore artificially increase the number of reinfections and underestimate the protective effect of the immune system after going through an infection
There is every reason to carry out an extensive analysis of the PCR results of the passengers of these two flights on 26 November in the short term. Both of their first PCR test and the next. Plus information about the seat numbers in the aircraft and the location in relation to those who had a low CT value after arrival at Schiphol and were the people who brought virus particles into space. If the information about the 18 who carried the Omicron variant is also linked to this, it gives an even more insightful picture.
N.B. Meanwhile, the GGD-Kennermerland reports that in the last week 14% of arriving passengers from South Africa have a positive PCR test, while they had all presented a negative PCR test on departure. This percentage of 14% also does not match the current incidence in South Africa. Not to mention the fact that they apparently took a negative PCR test on departure. That also cries out for a quick and in-depth analysis of what is going on now and that can be done partly by analyzing and announcing the CT values of the tests.
