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The World Health Organization (WHO) recently announced its recommendations for the composition of the influenza vaccine in the Southern Hemisphere for 2020.

The WHO Collaborating Centre for Reference and Research on Influenza located at the Doherty Institute in Melbourne routine collects and analyses circulating influenza viruses which it receives through the WHO Global Influenza Surveillance and Response System (GISRS).

Twice a year, in February and September, the Centre in Melbourne reviews its surveillance data along with data from the four other such Collaborating Centres around the world at the WHO Consultation on the Composition of Influenza Vaccines.

Since it takes approximately six months to manufacture and distribute influenza vaccines, decisions about which virus strains should be included in each year’s vaccine need to be made in ahead of the influenza season in the southern and northern hemispheres. Centre Director Professor Kanta Subbarao, Deputy Director Professor Ian Barr and Head of Epidemiology Associate Professor Sheena Sullivan attended the most recent WHO Consultation, which was held in Geneva, Switzerland in September.

The WHO consultation in September is especially important for the Centre at the Doherty Institute, as it is the only WHO Collaborating Centre for Influenza in the southern hemisphere, and the samples from the winter months here are important for providing information on the most recently circulating viruses. In 2019, with an early influenza season that started during the interseasonal period of the 2018-2019 Australian summer, the Centre has been particularly busy, receiving an unprecedented number of viruses throughout the year. 

“We have had an unusually long and busy period of influenza activity in Australia in 2019, with a variety of influenza viruses circulating, starting with A(H1N1)pdm09 viruses in the interseasonal period early in the year. This was followed by an early season in which A(H3N2) viruses dominated for a few months till they were replaced by influenza B viruses,” says Professor Subbarao, reflecting on the recent influenza season in Australia.

Recommendations arising from the September consultation are made for use in the following year the southern hemisphere, which includes Australia and New Zealand. Additionally, a number of countries in the tropical zone such as the Philippines, Thailand and Malaysia have influenza seasons that match closest to ours even though they lie in the northern hemisphere.

Following the Consultation, WHO made the following recommendation:

It is recommended that quadrivalent vaccines for use in the 2020 southern hemisphere influenza season contain the following:

• an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
• an A/South Australia/34/2019 (H3N2)-like virus;
• a B/Washington/02/2019-like (B/Victoria lineage) virus; and
• a B/Phuket/3073/2013-like (B/Yamagata lineage) virus.

It is recommended that trivalent vaccines for use in the 2020 southern hemisphere influenza season contain the following:

• an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
• an A/South Australia/34/2019 (H3N2)-like virus; and
• a B/Washington/02/2019-like (B/Victoria lineage) virus;

These recommendations includes changes in the A(H1N1)pdm09, A(H3N2) and B/Victoria lineage components of the vaccine. The recommendations are based on a combination of genetic and serological data obtained by analysis of recently circulating viruses. In serological analysis, surface proteins of circulating viruses are characterised using blood serum samples derived from ferrets (ferret antisera).

The A(H1N1)pdm09 component was updated to that included in the northern hemisphere 2019-2020 vaccine. The A(H3N2) vaccine was updated to A/South Australia/34/2019 because a larger proportion of recently circulating A(H3N2) viruses were well-inhibited by ferret antisera produced against A/South Australia/34/2019 compared to those produced against previous vaccine strains A/Switzerland/8060/2017 (Southern Hemisphere 2019) and A/Kansas/14/2017 (Northern Hemisphere 2019-2020). This is the third consecutive change in the recommended strain for the A(H3N2) component of the influenza vaccine, reflecting the ongoing evolution of circulating A(H3N2) viruses. The B/Victoria component of the recommended vaccine has also changed because in most countries the predominant proportion of circulating influenza B viruses were similar to B/Washington/02/2019 and different from the previous vaccine virus (B/Colorado/6/2017). Notably, the new B/Victoria lineage component (B/Washington/2/2019) contains a three amino acid deletion in the sequence of its haemagglutinin (HA) protein, whereas the previously recommended strain contained a two amino acid deletion in its HA protein.  

The newly recommended A(H3N2) vaccine virus, A/South Australia/34/2019, was first isolated as a candidate vaccine virus by the Centre in Melbourne. In total, three of the viruses recommended for inclusion in the quadrivalent vaccine the 2020 southern hemisphere influenza season were originally isolated as candidate vaccine viruses at the Centre.

While WHO makes recommendations for the influenza vaccine, it is up to national authorities to decide on the final composition for their individual countries, usually taking into account the WHO recommendation. The Australian Influenza Vaccine Committee met in Canberra on October 9 and made the same recommendation as the WHO for the 2020 influenza season.

All current recommendations: http://influenzacentre.org/surveillance_vaccines.htm

Full WHO recommendations: https://www.who.int/influenza/vaccines/virus/recommendations/2020_south/en/

Recommendations for the Australian influenza vaccine in 2020: https://www.tga.gov.au/aivc-recommendations-composition-influenza-vaccine-australia-2020