INFLUENZA A/ASTRAKHAN/3212/2020 (H5N8)-LIKE STRAIN (CBER-RG8A) (CLADE 2.3.4.4B)

INFLUENZA A/ASTRAKHAN/3212/2020 (H5N8)-LIKE STRAIN (CBER-RG8A) (CLADE 2.3.4.4B) is the active substance in Zoonotic Influenza Vaccine Seqirus, a vaccine authorised in the European Union for the prevention of flu caused by H5 strains of the influenza A virus, also known as avian influenza or bird flu.^[4]

• What is Influenza A/Astrakhan/3212/2020?
• How does Influenza A/Astrakhan/3212/2020 work?
• Which conditions is it used or studied for?
• How is Influenza A/Astrakhan/3212/2020 given?
• What do the clinical trials show?

What is influenza A/Astrakhan/3212/2020?

Influenza A/Astrakhan/3212/2020 is a vaccine substance based on surface antigens of an H5N8 influenza A virus strain belonging to clade 2.3.4.4b.^[5] It is classified as a purified antigen influenza vaccine, with the ATC code J07BB02.^[2] The substance is described in the registry as a structurally diverse substance of vaccine origin.^[2]

The vaccine is marketed under the name Zoonotic Influenza Vaccine Seqirus and contains surface antigens (haemagglutinin and neuraminidase) of the H5N8 strain, grown in fertilised eggs from healthy chicken flocks, inactivated, and adjuvanted with MF59C.1.^[5] It received a marketing authorisation in the European Union, held by Seqirus S.r.l., with authorisation records EU/1/23/1761/001 and EU/1/23/1761/002.^[2]

How does influenza A/Astrakhan/3212/2020 work?

This vaccine is designed to stimulate the immune system to produce antibodies against the H5N8 virus strain. It contains the surface proteins haemagglutinin and neuraminidase from the A/Astrakhan/3212/2020 (H5N8)-like strain, at a dose of 7.5 micrograms of haemagglutinin per 0.5 ml dose.^[5] The MF59C.1 adjuvant contains squalene, polysorbate 80, sorbitan trioleate, sodium citrate and citric acid, and is included to enhance the immune response to the vaccine.^[5]

The trials measure the immune response through haemagglutination inhibition (HI) antibody titres, which show how well antibodies can block the virus from attaching to cells, and microneutralisation (MN) antibody titres, which show how well antibodies can neutralise the virus.^[2][3]

Which conditions is it used or studied for?

• Avian influenza (H5N8) — the vaccine is authorised for prevention of flu caused by H5 strains of influenza A virus, also known as avian influenza or bird flu.^[4]
• Virus diseases — one trial lists virus diseases as the condition studied, reflecting the vaccine's role in preventing viral infection.^[3]
• Avian influenza and seasonal influenza — one trial studies the vaccine together with seasonal influenza vaccines, comparing immune responses.^[1]

How is influenza A/Astrakhan/3212/2020 given?

The vaccine is given as a suspension for injection in a pre-filled syringe, by intramuscular injection.^[2] Each pre-filled syringe contains 0.5 ml of the suspension, and the product is available in packs of 1 or 10 pre-filled syringes.^[5] The trials used a two-dose schedule, with the second dose given at least 21 days after the first dose in one trial.^[1]

What do the clinical trials show?

Three phase 3 trials in the EU Clinical Trials Information System have tested this vaccine. All three trials are interventional studies, and their status is either completed or authorised.^[2][3][1]

The largest trial enrolled 300 participants and studies the vaccine together with seasonal influenza vaccines, measuring seroconversion proportion three weeks after the second dose using the microneutralization test.^[1] The smallest trial enrolled 60 participants and compares adults previously vaccinated with an H5N1/MF59 influenza vaccine about 20 years earlier with adults never vaccinated against H5 influenza.^[2] A third trial enrolled 180 participants and compares adults previously primed with the PanFluVac Matrix M adjuvanted H5N1 influenza vaccine with H5N1 vaccine-naive participants.^[3]

The primary outcomes in two trials are HI and MN antibody titres against the H5N8 clade 2.3.4.4b strain, measured at baseline and 28 days after the first and second doses.^[2][3] The third trial measures seroconversion proportion in all study subjects three weeks after the second dose.^[1]