The immunologist Marc Veldhoen frequently debunks myths and disinformation about Covid. His main focus is the anti-vaccine movement but he also regulary outlines false interpretation and limitations of highly cited studies about COVID-19. I remember that Veldhoen’s statements were/are often devaluated about immunity developing after infection, calling him a denier of the pandemic and/or long covid. I follow his postings for quite some time now and I’m convinced it’s unjustified to judge in such a way about him.
So I will propose another approach: I’m ignoring how he presents his critical statements, his analysis of research papers or accusing the „zerocovid bubble“ of scaremongering. It may appear inappropriate at times but I’m only interested in facts and methods leading to conclusions. I’m not an expert in immunology, let alone the interpretation of methods and biases. Why only him? Because there is almost nobody on Bluesky, as far as I know, who also regularly points to limitations and poor method/data quality in respective papers. Immunologist and Science Communicator Prof. Sheena Cruickshank announced planning „some basic immunology explainer blogs“ recently. If you know more accounts, regardless of language, please let me know in the comments, thank you!
Veldhoen also has a Substack newsletter. He’s mostly active on Bluesky where he writes more or less detailed threads about claims and discussed papers. I will collect many threads here and try to give a short summary as soon as I have time for it.
One thing: I will focus on disinformation coming from the „zero covid bubble“. People reading my blog will be mostly covid aware and won’t fall for anti-vaxxer, pandemic denying propaganda. They may have, however, a blind spot for false and misleading statements from experts they follow („confirmation bias“).
Immune Damage
Veldhoen, 24.07.25 (thread): Vulnerable, elderly men are more susceptible for other infections than the general population. Real damage would already be visible in detecting much more opportunistic and established infections. None of this is present.
Brain Damage
Mohammadi-Nejad et al.: Accelerated brain ageing during the COVID-19 pandemic (07/2025)
Veldhoen, 23.07.25 (thread): Weakness in methods (only 2 time points), other infections have a smiliar effect. Authors also conclude that the pandemic accelerated brain ageing regardless of infection, suggesting social factors.
Veldhoen, 07.10.25 (thread): Brain is flexible, constantly modified. Inflammatory response has systemic effects. Genes and their products involved in many processes. The latter is important in many aspects. Genes and proteins play diverse roles, such as in tissue repair and cell proliferation. That some are also found in cancer, makes their increased presence not mean there is cancer (or damage or dementia or autoimmunity, etc). The inflammatory response also reaches the brain. Some cells in the brain, such as microglia, will respond and signal back. This can temporarily mean changes, such as thickness in some areas, and alterations in the blood-brain barrier. But that does not mean it is damaged. The brain is very plastic. It can handle a lot, and that it plays a role in responding to inflammation is well known. To provide an example of how plastic it is.
In LC patients, the inflammatory response is longer, hence you have a more systemic response. That is not serious damage. Dysregulation? It is away from steady state, immune mediators such as CCL11 are produced in immune naive.
It can take some time to return to base levels, in some longer than in others. This was the same during the flu pandemic. Did everyone get brain damage or lose their intelligence? No, nor will we now. Most recover and go on, protected by immunity. In that context, it should be viewed. Of course, the titles may be suggestive. And yes, things change; you have undergone an infection after all, especially when you are older and less healthy. And then they settle back for most of us. But if you are immunocompromised or elderly, it can be more damaging. Your body, your cells, are less flexible. That is why this group needs extra immune support, and many infections, from chickenpox to influenza and COVID, can have a negative impact. Can you measure changes? Yes, you can. Does that mean damage or permanent issues, or loss of cognitive function? Without immunity or weaker immunity, there is a greater risk, like with every infection. But SARS-CoV-2 is like the others.
MECFS/Long Covid
Shankar et al.: Oxidative stress is a shared characteristic of ME/CFS and Long COVID (04/2025)
Veldhoen, 18.07.25 (thread): Likely inflammatory cause for both conditions, causing increased ROS production in lymphocytes which are inappropriately reduced thereafter, causing hyperproliferation. Could explain many symptoms like fatigue (t-cell activation costs energy). Metformin may reduce this effect. Limited therapy options available, however, research with great challenges (see Forman and Zhang 2021).
Veldhoen, 23.04.25 (thread): Post-acute Conditions are not unique to SARS-CoV2, there is a long history of PAIS (post acute infection syndroms)
Veldhoen, 22.11.24 (thread): Comprehensive summary of MECFS, explicitely naming immunological causes in contrast to some neurologists claiming a pure psychiatric cause (unjustified).
Disinformation
Claim that Covid disseminates throughout the body, with manipulated, mislabeled images by e.g. Danielle Beckmann or Spela Salamon, all part of the same group – scientists from the World Health Network.
Veldhoen: The data is mouse, is not virus but i.v. injected fluorescently labelled protein. The Influenza virus HA protein, or the Spike protein from SC2. The latter does not travel much, so the picture of S1 is abused.