NHS chiefs are worried pressures on the NHS may deter people coming forward with symptoms.
It's the most significant drop since the Omicron wave hit the country in December, the figures suggest.
The death toll, worst in poorer countries and among the under-fives, needs urgent action, experts say.
Other groups have reported higher protection, but the results are still seen as a triumph.
A question everyone's asking: what's my Covid risk? Here's how to find out.
Borrowing - which hit a record £22.3bn in October - cannot go on indefinitely, chancellor says.