Summaries by Irina Yakutenko
Writer and Science Journalist
Released 16 September 2020
Complete transcript is here
- The main topic of the conversation was epidemiological situation in Africa. To make long story short: no one knows for sure what’s going on there. There are several papers that make us think that they are approaching herd immunity – at least in clusters. However it’s impossible to make any robust conclusions as there are a lot of methodological flaws and lack of good data.
- One of the best papers came from Kenia (https://www.medrxiv.org/content/10.1101/2020.07.27.20162693v1.full.pdf). Researchers assessed seroprevalence in Kenyan blood donors and found that 5% of donors had antibodies as early as in May. In big cities such as Nairobi and Mombasa seroprevalence was even higher – up to 9,3%. But in that research they used self-made ELISA tests – probably because commercial tests were not available in Kenya at that time. And with such tests no one can be sure that the results are really sound.
- From the other hand, even if commercial tests would be available in Africa, we can not fully trust them. These tests were made and validated in countries with much lower infection prevalence and when using in African population, their PPV (positive predictive value) is low. Drosten’s colleague Felix Drexler determined that commercially available 12 SARS-CoV-2 ELISAs showed up to 25% false-positive results depending on antigen and antibody types (https://www.researchgate.net/publication/342792434_Diagnostics_and_spread_of_SARS-CoV-2_in_Western_Africa_An_observational_laboratory-based_study_from_Benin). (Study was made in Benin).
- Data about deaths are also scarce. It seems that there are less deaths in cities than we would expect. But urban population in Africa is much younger than in the country – that’s the first reason. The second – they don’t test enough in the country. Testing is poor even in the biggest cities. For example since SARS-CoV-2 came in Kenya in March there have been done 320 000 tests. It’s comparable with the number of tests Germany did in March weekly.
- We don’t know whether immune system of people who live in Africa reacts to the virus the same way as ours. In that region there are a lot of infections, parasites etc. Immune cells are trained to recognize different pathogen patterns – and much more of them than can recognize immune cells of people in the Western world. May be that “pathogen immune library” could help to combat coronavirus.
- Drosten mentioned that he had private communications with virologist from South Africa who told him that seroprevalence in pregnant women from poorest districts of Cape Town is 40%. Drosten didn’t specify which test did health workers use there but anyway it’s a huge number. At the same time excess mortality in Cape Town was 3900 people. Using these numbers one can calculate that IFR here is 0,28. Given that not all Cape Town residents are poor (and richer citizens have lesser chance to catch virus so total seroprevalence is lower), adjusted IFR is somewhere about 0,6 – more or less the same is European countries.
- At the end of the episode Prof. Drosten told a little bit about this letter to NEJM about masks having a potential for sort of variolation (https://www.nejm.org/doi/full/10.1056/NEJMp2026913). He regarded this hypothesis as an interesting academic speculation but noticed that it would be very hard to translate it into any practical guidelines.
Released 9 September 2020
Complete transcript is here
- We still don’t know how many people have asymptomatic COVID-19. But we know that there could be a lot more cases that we find out with PCR testing. Frau Ciesek told about influenza research (pity there is no link) when people investigated how many people have virus in the time of outbreak using PCR test and after that using antibody test. During the outbreak they found virus in 16% of patients and their contacts. After the outbreak it turned out that 85% of people they’ve checked for influenza antibodies had them.
- One more hypothesis explaining how it could be that asymptomatic have the same amount of virus as symptomatic but differ so much in the disease course. The idea is as follows: though we detect the same viral RNA concentration on the peak, in people who don’t exhibit any symptoms it fades much faster than in symptomatic. By the time there are no reliable proof of that assumption and some research showed that asymptomatic shed virus even longer. But it could be that after the peak is passed total amount of virus particles is much smaller in them as opposed to people with symptoms.
- In autumn and winter we will have both influenza and COVID-19. The symptoms are more or less similar and it could be hard to distinguish which virus a patient has. Frau Ciesek mentioned a method to do that – multiplex PCR. I’ve read about this method in COVID-19 research but only as a way to detect it more precisely (for example https://www.sciencedirect.com/science/article/pii/S1386653220302419?via%3Dihub). The idea of using it with primers to influenza and SARS-CoV-2 sounds new to me.
- A proposal how we can change airport testing. At the moment we make tests right after people return from red zones. But using this testing strategy we possibly miss a lot of cases as people could get infected in the last days of their journey or right in the foreign airport. To prevent the spread of infection we should oblige all travelers who were in red zones to quarantine for five days (mean incubation period) and make test after that.
- An interesting notice about running nose and COVID-19 in kids. Researchers from Robert Koch institute (https://www.rki.de/DE/Content/InfAZ/N/Neuartiges_Coronavirus/Projekte_RKI/KiTAStudie_Juli.pdf?__blob=publicationFile) found out that a single symptom we see it in 3,5% of cases. But along with other symptoms it is detected in good 18% of cases.
Released 1 September 2020
Complete transcript is here
- There are many variants of SARS-CoV-2. There are relatively weak data that some of them can infect cells in cell culture better than others. But it’s too early to say whether these results are real and whether they could be directly translated to humans.
- Robert Koch Institute does very good job and numbers of new incidents in Germany are more or less correct. Apparently, the true numbers are bigger then what we have, but not too much. We can say that because we see these jumps in daily statistics – if there were a constant increase, we would see more stable behavior of the graph. And the reason for low incidence is not test scarcity –we are doing a lot of tests.
- We already know that SARS-CoV-2 tends to spread in clusters. And while the total number of incidences is low the situation looks stable. But there is a threshold and when number of incidences overpasses it, we can suddenly get a rapid increase in numbers and new cases all over the population. Christian tried to describe the model that explains that phenomenon on TWiV. In his podcast he used a couple of metaphors. The first is coffee filter metaphor. When you start pouring water at coffee filter, at the beginning there comes no water from the bottom of the filter – though the filter itself becomes more and more wet. And suddenly the amount of water becomes too big, and a lot of drops start to fall constantly. Another metaphor is more complicated. Drosten described this Connect Four game in which you drop red and yellow discs into the grid (and to win you have to form a horizontal, vertical, or diagonal line of four discs). When the ratio between red and yellow discs is 50 to 50, we will almost always have a connection between clusters of for example red color – but not through the whole grid. When the ratio changes to 80 to 20, the probability that red discs would be connected to each other throughout the whole grid is almost 100%. The same pattern we observe with the incidence numbers in clusters. And if our grid has two electrodes in two angles and red disks are from metal and yellow disks are from wood, with rising number of reds we will suddenly have a current – rapid increase in case number.
- At the moment Germany performs enough tests, but it will be hard to do simultaneously school and airport testing. Labs are now almost overwhelmed.
- Drosten offers chip method to stop community spreading without additional testing. Every week people should write down, whether they were in “cluster situations”. When someone gets infected, he can tell healthcare worker about all these potentially dangerous situations. This method should ease contact tracing. Also it would be useful if local healthcare authorities make a list of typical “cluster situations” to help people to remember.
- Drosten offers to make decision about isolation more flexible. If someone has symptoms and becomes positive PCR-test results four days after that happened, there is no sense in 14-days isolation. All research results point out that after 4-7 days after symptoms ongoing virus carrier can not infect other people.
- Labs in Germany are working to make rapid test (antigen test). If everything will go smoothly, it could be certified in December.