A study in Nature Neuroscience in January 2023 explores the role of COVID-19 infection on the brain and demonstrates that the MVA-CoV2-S vaccine candidate has potential against infection. The study, led by researchers at Seville University uses a mouse model to characterise the effect of infection on the nervous system.  

COVID-19 and the brain 

The study indicates that COVID-19, although “primarily a respiratory disease”, has caused many patients to display neurological symptoms. These include anosmia and ageusia, headaches and dizziness, or more severe conditions such as cognitive impairment to encephalopathy. The authors note that these symptoms have been attributed to the “secondary effects of the systemic SARS-CoV-2 infection” or direct infection of the central nervous system (CNS). However, SARS-CoV-2 has also been detected in the brain of several experimental animal models and natural hosts.  

The three main suggested routes of entry for SARS-CoV-2 to the CNS are: 

  • “The so-called olfactory route” 
  • The haematological route 
  • Retrograde transport through peripheral nerves innervating the respiratory tract 

Whatever the pathogenic mechanism, this study identifies the pre-established neuropathological alterations in patients with severe COVID-19.  

Vaccines against COVID-19 

The study recognises that “many vaccine candidates” have been developed, tested, and approved, using “various technologies”. Although they are being used for mass vaccination, it remains unknown whether they “prevent viral spread to other regions of the body”. 

The advantages of a poxvirus modified vaccinia virus Ankara (MVA) vector expressing a human codon-optimised, full-length SARS-CoV-2 protein, known as MVA-CoV2-S, have been “previously described”. The study indicates that it is a “promising” candidate. It induces “robust and long-term” immune responses in mice. Furthermore, it also offers efficacy against SARS-CoV-2 infection in other animal models.  

In this study, they investigate the potential efficacy of MVA-CoV2-S vaccination against “cerebral infection and associated damage in K18-hACE2 mice”. This is a “well-established mouse model of severe COVID-19 disease”.  

The study 

The researchers immunised mice with one or two doses of the vaccine and analysed its capability to protect against infection and damage to the brain. Dr Juan García-Arriaza described “spectacular” results. They demonstrated that even a single dose “completely prevents SARS-CoV-2 infection in all brain regions studied” and “prevents associated brain damage”.  

“This demonstrates the great efficacy and immunogenic power of the vaccine that induces sterilising immunity in the brain.”  

The results are “compatible with the neurological pathology observed in patients with COVID-19, said Professor José López-Barneo. The authors state that their work complements previous work to establish the “potent immunogenicity and full efficacy” of the candidate in different animal models. Thus, they recommend the evaluation of the vaccine in clinical trials.  

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