Professor Sir Ian Diamond, head of the Office for National Statistics (ONS), said there was a lot of regional variation in terms of how many people have antibodies.
His comments come after England's chief medical officer Professor Chris Whitty said there were still risks to reopening society and the UK would experience another surge of cases at some point, potentially in late summer or through the autumn and winter.
Sir Ian said people needed to understand how the data was moving forward and look at the impact of the "wonderful" vaccine rollout.
"But having said that, we need also to recognise that this is a virus that isn't going to go away," he told The Andrew Marr Show on BBC One.
"And I have no doubt that in the autumn there will be a further wave of infections."
Asked if it is too early to know how much of the fall in infections across the UK is down to the vaccine rollout, Sir Ian said there were a number of moving parts such as vaccines and restrictions.
He told the programme: "I mean I would say though that this has been an incredibly impressive vaccine rollout and we've been looking at antibodies in the population and we've been scaling up our survey in order to be able to take many more blood tests so that we can look at the impact.
"And what we're seeing is quite remarkable increases in the level of antibodies in the over-80s, and increasingly in the over-70s. So I'm very, very confident that the vaccine rollout is really starting to provide some real protection.
"At the other side, we see very relatively high levels amongst young people, which just shows how much of young people have been affected by the virus.”
During the week, Prof Whitty said he would "strongly advise" against any move to shorten the timetable for easing lockdown restrictions.
Speaking to the Commons Science and Technology Committee, Prof Whitty said the measures pencilled in for May 17 in England, when indoor mixing of up to six people could be allowed, involved "significant risks".
Modelling considered by the Scientific Advisory Group for Emergencies (Sage) has suggested that even under the most optimistic set of assumptions, at least a further 30,000 Covid-19 deaths could occur.
Prof Whitty said: "What we are going to see is, as things are opening up, what all the modelling suggests is that at some point we will get a surge in virus.
"We hope it doesn't happen soon. It might, for example, happen later in the summer if we open up gradually or because of the seasonal effect, it might happen over the next autumn and winter.
"All the modelling suggests there is going to be a further surge and that will find the people who either have not been vaccinated or where the vaccine has not worked.
"Some of them will end up in hospital and sadly some of them will go on to die."