Popularization of research advances on COVID-19

A new type of vaccine ?

To be effective against SARS-CoV-2, a vaccine needs to generate a significant number of neutralizing antibodies targeting the spike viral protein (a surface protein). But to achieve this, a viral antigen needs to be transported and expressed. It now seems possible to use an already-existing vaccine, that which is used and is effective against yellow fever.

The vaccine against yellow fever YF17D prompts a broad innate, humoral and long-term protective cellular immune response. These advantageous characteristics make it possible to use its matrix as a vector to design other vaccines such as that used against dengue. This matrix, a small form of the RNA of a living, attenuated  yellow fever virus, tolerates the insertion of foreign antigens amongst its viral proteins.

What is the best way to use this against COVID? Researchers have just succeeded  in constructing a recombinant virus on the basis of the YF17D strain, making it express the antigen of the SARS-CoV-2 surface spike, thereby rendering it less virulent.

This candidate vaccine was tested on hamsters. The animals were vaccinated on day 0 with the candidate vaccine or with a placebo. On day 7 a second injection was carried out. On day 21, all the hamsters vaccinated with the candidate vaccine had developed specific neutralizing antibodies against the spike protein.

After 23 or 28 days, inoculation of the hamsters with SARS-CoV-2 was carried out intranasally.

This can be represented schematically as follows:

In this way it was shown that vaccination enabled the viral charge to be reduced significantly, producing neutralizing antibodies and avoiding signs of pneumopathy. But what about the cellular immune response? This was studied in mice. The candidate vaccine enabled a significant cellular response, dominated by T CD8+ lymphocytes (cytotoxic). Finally, the vaccine was tested in monkeys (macaques) using a single injection. The vaccinated monkeys developed high levels of neutralizing antibodies targeting the spike protein, enabling a reduction of the viral charge. This immune response only appeared 10 days after vaccination. This vaccine could be an ideal candidate in the fight against COVID-19.
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