Phylogenomic analysis of Uganda influenza type-A viruses to assess their relatedness to the vaccine strains and other Africa viruses: a molecular epidemiology study
Authors: Nabakooza Grace , Collins Owuor David , de Laurent Zaydah R. , Owor Nicholas , Timothy Kayiwa John , Jjingo Daudi , Nyaigoti Agoti Charles , James Nokes David , Patrick Kateete David , Mulindwa Kitayimbwa John , David William Frost Simon , Julian Lutwama Julius 
Published: July 2021

Background

Genetic characterisation of circulating influenza viruses is essential for vaccine selection and mitigation of viral transmission. The current scantiness of viral genomic data and underutilisation of advanced molecular analysis methods on influenza viruses circulating in Africa has limited their extensive study and representation in the global influenza ecology. We aimed to sequence influenza type-A viruses (IAVs) that previously circulated in Uganda and characterised their genetic relatedness to the vaccine viruses and publicly available Africa IAVs.

Methods

This was an observational study nested to the Uganda national influenza surveillance programme. We used Next-generation sequencing to locally generate genomes from 116 A(H1N1)pdm09 and 118 A(H3N2) viruses collected between 2010 and 2018 from 7 districts across Uganda. A total of 206 hemagglutinin (HA), 207 neuraminidase (NA), and 213 matrix protein (MP) sequences were genetically compared to the WHO-recommended vaccines and other viruses isolated from Africa since 1994. Viral temporal and spatial divergence and circulating genetic clades were characterised using phylogenetic methods.

Findings

We successfully generated gene sequences for 91·9% (215/234) viruses. Uganda A(H1N1)pdm09 and A(H3N2) virus HA, NA, and MP proteins had 96·36-99·09%, 96·49-99·39%, and 97·48-99·95% amino acid similarity, respectively, to vaccines recommended from 2010 through 2020. The local viruses incorporated amino acid substitutions (AAS) in their antigenic, receptor binding, and glycosylation sites each year causing them to antigenically drift away from vaccines. For seasons when vaccine formulations differed, Uganda IAV antigenic sites had 1-2 extra AAS relative to the Southern than Northern hemisphere vaccine viruses. All Uganda IAVs carried the adamantine-resistance marker S31N but not the neuraminidase inhibitor (NAI) resistance markers H274Y and H275Y. However, some A(H1N1)pdm09 viruses had permissive substitutions V234I, N369K, and V241I typical of NAI-resistant viruses. The 2017-2018 A(H1N1)pdm09 viruses belonged to global genetic clade 6B.1, while the A(H3N2) viruses isolated in 2017 belonged to clades 3C.2a and 3C.3a. Uganda IAVs obtained before 2016 clustered distinctly from other Africa viruses while later viruses mixed with other Africa, especially Kenya and Congo, and global viruses. Several unique viral lineages (bootstrap >90) persisted in Uganda and other countries for 1-3 years.

Interpretation

The study reveals Uganda as part of the global influenza ecology with continuous importation, antigenic drift, and extensive local transmission of IAVs, presenting a potential risk of future outbreaks. For a country with limited health resources and where social distancing is not sustainable, viral prevention by vaccination should be prioritized. The notable viral diversity in Africa is a warning to countries to broaden and incorporate genome analysis in routine surveillance to monitor circulating and detect new viruses. This knowledge can inform virus selection for vaccine production and assist in developing cost-effective virus control strategies.

Funding

This work was supported by the Makerere University-Uganda Virus Research Institute Centre of Excellence for Infection and Immunity Research and Training (MUII). MUII is supported through the Developing Excellence in Leadership, Training and Science (DELTAS) Africa Initiative (Grant no. 107743). The DELTAS Africa Initiative is an independent funding scheme of the African Academy of Sciences (AAS), Alliance for Accelerating Excellence in Science in Africa (AESA), and supported by the New Partnership for Africa’s Development Planning and Coordinating Agency (NEPAD Agency) with funding from the Wellcome Trust (Grant no. 107743) and the UK Government. The work was also funded in part by a Wellcome Trust grant (102975).