Please cite both the package and the original articles in your
publications:

  Gruson H (????). “contactdata: Social Contact Matrices for 152
  Countries.” R package version 1.1.0.9000,
  <https://CRAN.R-project.org/package=contactdata>.

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {{contactdata}: Social Contact Matrices for 152 Countries},
    author = {Hugo Gruson},
    note = {R package version 1.1.0.9000},
    url = {https://CRAN.R-project.org/package=contactdata},
  }

  Prem K, Cook AR, Jit M (2017). “Projecting social contact matrices in
  152 countries using contact surveys and demographic data.” _PLoS
  Computational Biology_, *13*(9), e1005697.
  doi:10.1371/journal.pcbi.1005697
  <https://doi.org/10.1371/journal.pcbi.1005697>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Projecting social contact matrices in 152 countries using contact surveys and demographic data},
    author = {Kiesha Prem and Alex R. Cook and Mark Jit},
    journal = {PLoS Computational Biology},
    year = {2017},
    volume = {13},
    number = {9},
    pages = {e1005697},
    doi = {10.1371/journal.pcbi.1005697},
  }

  Prem K, van Zandvoort K, Klepac P, Eggo RM, Davies NG, Group CCW,
  Cook AR, Jit M (2021). “Projecting contact matrices in 177
  geographical regions: An update and comparison with empirical data
  for the COVID-19 era.” _PLoS Computational Biology_, *17*(7),
  e1009098. doi:10.1371/journal.pcbi.1009098
  <https://doi.org/10.1371/journal.pcbi.1009098>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Projecting contact matrices in 177 geographical regions: An update and comparison with empirical data for the COVID-19 era},
    author = {Kiesha Prem and Kevin {van Zandvoort} and Petra Klepac and Rosalind M. Eggo and Nicholas G. Davies and CMMID COVID-19 Working Group and Alex R. Cook and Mark Jit},
    journal = {PLoS Computational Biology},
    year = {2021},
    volume = {17},
    number = {7},
    pages = {e1009098},
    doi = {10.1371/journal.pcbi.1009098},
  }