Laviai Nielsen

Laviai Nielsen (born 13 March 1996) is a British sprinter specialising in the 400 metres.

In 2015, she took a gold medal in the 400 m at the European Junior Championships. She won several medals as a member of the Great Britain 4x400 metres relay teams, including silver at the 2017 World Championships in the women's 4 x 400 metres, and at the 2023 World Championships in the mixed 4 x 400 metres, and bronze in the women's 4 x 400 metres at the 2022 World Championships. She won two bronze medals at the 2024 Summer Olympics as part of both British 4 x 400 metres relay teams, mixed and women categories. Nielsen has an identical twin sister, Lina Nielsen, who is also an international athlete in the same events, but who has moved into 400-metre hurdles in recent years. In August 2022, Nielsen disclosed that she had been diagnosed with multiple sclerosis in the summer of 2021.

Her twin sister Lina had been diagnosed with the same condition some years earlier, and, as it has genetic properties, Nielsen was tested for the illness.