Whooping-cough cases have been rising in England and many other countries since the beginning of the year.
It is cyclical, with peaks every three to five years.
The last was in 2016.
But numbers fell during the pandemic, leaving “a peak year overdue”, according to the UKHSA, and less immunity in the population.
Vaccination rates among pregnant women are also a factor – with 58.9% uptake of jabs in March 2024 compared with a high of 72.6% in March 2017.
UKHSA immunisation director Dr Mary Ramsay said: “Ensuring women are vaccinated appropriately in pregnancy has never been more important.
“Pregnant women are offered a whooping-cough vaccine in every pregnancy, ideally between 20 and 32 weeks.
“This passes protection to their baby in the womb so that they are protected from birth in the first months of their life, when they are most vulnerable and before they can receive their own vaccines.
“Our thoughts and condolences are with those families who have so tragically lost their baby.”
