UK Health Security Agency chief executive Prof Dame Jenny Harries has announced that she will leave the organisation she has headed since its foundation in 2021.
Harries said she was "immensely proud" of what the agency has achieved since its creation in the months following the arrival of the Covid-19 pandemic.
"We started building the agency mid-pandemic and since then we have created a genuinely unique and world-leading public health agency with strong partnerships across public, private, domestic and international organisations," she said.
"I have been privileged to work alongside UKHSA’s highly skilled, multidisciplinary and talented workforce who are dedicated to the agency’s mission of protecting the public’s health. I would also like to thank all those colleagues in frontline services with whom I’ve worked for many years, especially those in local authorities, the NHS and in social care.
"It has been a privilege to lead the agency from day one but I am now excited about doing something new in the next phase of my career, while continuing to champion the agency’s work."
Chief medical officer for England Prof Sir Chris Whitty said Harries' "unrelenting commitment to supporting the public" had been "extraordinary".
"I am profoundly thankful for her leadership, advice and proactiveness in tackling the toughest of tasks," he said. "Her contribution to public health has been remarkable."
Harries is due to leave her post in early summer.
UKHSA also announced that chief medical officer Prof Isabel Oliver is leaving the organisation following her appointment as chief medical officer for Wales.
Oliver led the development of UKHSA’s science strategy and the delivery of many of its scientific functions and services – including creating a new vaccine-development and evaluation centre at UKHSA’s Porton Down campus in Wiltshire.
In her new role she will replace Dr Frank Atherton, who recently retired.
Oliver said it had been an honour to serve as UKHSA’s first chief scientific officer and lead an excellent team of public health scientists and clinicians.
"In an age of unprecedented health security challenges, we have ensured that UKHSA secures health and prosperity working in partnership with industry and academia and strengthening our preparedness," she said.
"Although I will miss UKHSA hugely, I look forward to continue working with the agency in my new role."
UKHSA chair Ian Peters said Oliver had brought "deep experience and vision" to the agency.
"We thank her for her leadership of our science strategy and the creation of significant new capabilities which have been built or are in development," he said.
"We wish her the very best in her new role."