Response to Dr. Bhakdi

I herewith wanted to react to a recent video posted by Dr. Bhakdi (

I was quite stunned about the statements he made and could not believe that this had allegedly been published. Hence, I consulted the publications Dr. Bhakdi has been referring to in his presentation (you’ll find them in the article that accompanies the video). My contribution attached explains why his viewpoint in regard of herd immunity and protection against variants is highly questionable. Given his background and credentials, I am very surprised at his conclusions. It’s certainly not that I cannot refrain from criticizing but if we’re not going to stick to the science, we’re going to lose our precious credibility.

I am sure many of you have seen Dr. Bhakdi’s presentation. As much as I’d like to confirm his position, I cannot agree with his interpretation. Dr. Bhakdi is basically claiming that because of previous exposure to common cold viruses we have immune memory cells that can be recalled upon exposure to Sars-CoV-2 and protect us! This is not true! While there is no doubt that there is some cross-reactivity between immune responses to some spike(S)-derived epitopes on beta coronaviruses (CoVs), these immune responses are not cross-PROTECTIVE.

Dr. Bhakdi is confusing all along cross-reactivity (which basically means that antibodies (Abs) or T cells induced by one CoV can BIND similar [conserved] epitopes on some other CoVs) and cross-protection. However, immune RECOGNITION does not equal immune PROTECTION. None of the publications Dr. Bhakdi is referring to has analyzed or claims cross-PROTECTION elicited by other CoVs. Again, Abs that bind to Sars-CoV-2 do not necessarily neutralize the virus and prevent it from entering the cell. Of course, many people will have a history of common cold infection and hence may rapidly recall some spike-directed Abs (i.e., towards epitopes that are shared with Sars-CoV-2) upon exposure to Sars-CoV-2 or after immunization with Sars-CoV-2-derived antigens. However, this doesn’t mean at all that these rapidly rising IgG and IgA Dr. Bhakdi is referring to will neutralize Sars-CoV-2 and protect you from Covid-19 disease! In addition, Sars-CoV-2-induced Abs were only found to cross-react with 2 out of the 4 common cold CoVs (i.e., only for beta coronavirus HKU1 and OC43) and the cross-reactivity was ‘much lower than that observed for the remaining CoV epitopes’.

Furthermore, his statement that people who have built immunity against CoV are automatically protected against all Sars-CoV-2 variants is not true either for exactly the same reasons (i.e., Abs that bind to variants do not necessarily neutralize them and could even be at risk of causing Ab-dependent enhancement of disease; ADE).

Last but not least, the publication of the Danish which Dr. Bhakdi is referring to does not truly provide information on asymptomatically infected individuals. The category labelled as ‘asymptomatic/ mild symptoms’ refers to individuals who recovered (inclusion criterion!) from disease, even if it was mild (outpatient, no limitation of daily activities). How could truly asymptomatically infected people have been eligible according to at least one of the inclusion criteria: ‘Full recovery from acute Covid-19 illness?’ Asymptomatically infected individuals do not develop long-lived or mature anti-S Abs and have not been reported to develop memory B cells or CYTOTOXIC memory T cells. Consequently, previously asymptomatically infected people (i.e, the majority of the population) cannot rely on ACQUIRED immunity for protection against infection or disease, respectively! In the Danish study at least nine individuals were unable to fully neutralize viral infection. If truly asymptomatic individuals were included, it would be reasonable to assume that those nine individuals figured among the group (n= 17) classified as asymptomatic/ mild. In addition, it is stated in the discussion that ‘some rare individuals have no detectable immunological memory to Sars-CoV-2’.

The same criticism also applies to the CD8+ T cell responses reported in this study: To my knowledge, there is no evidence that Sars-CoV-2-induced CD8+ T cells provide cross-protection from common cold viruses or vice versa and this wasn’t even part of this investigation. Cross-reactivity of Sars-CoV-2-CD8+ T cells with spike protein from MERS or Sars-CoV-1 was reported in this study but pre-existing immunity of study participants to these viruses is unlikely and can, therefore, not provide for a potential protective recall upon exposure to Sars-CoV-2.

So, with all my respect for Dr. Bhakdi, the conclusion that herd immunity would already be established and would simply need to be recalled upon exposure to Sars-CoV-2 is not correct. By the way, if this were true, we would not currently be witnessing a fulminant propagation of the delta variant in several countries. I agree , of course, that mass vaccination should immediately stop but not because we already reached herd immunity!!

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