Last month health and social care secretary Matt Hancock confirmed the government was 'ramping up' plans for an autumn booster campaign that could see practices deliver millions more COVID-19 jabs.
Top-up jabs are intended to protect the UK population against new variants, with Mr Hancock confirming that the government had already procured enough doses.
But Mr Zahawi told BBC Breakfast that a booster campaign could start as late as next year depending on how long initial doses of the vaccine protect patients.
Mr Zahawi stressed that a start date for the booster campaign would be determined by clinicians - adding that deputy chief medical officer Jonathan Van Tam was conducting research to determine which vaccine would offer patients the ‘greatest protection’.
The government has announced that more than 50m coronavirus vaccines have been administered in the UK, with over 34m people having had at least one jab while 15m have had both doses.
Speaking about the autumn booster campaign, Mr Zahawi said: ‘We want to give the scientists as many options to be able to deploy a booster.
‘The NHS team is already planning to be ready for deployment from September onwards, but the decision hasn’t been made as to whether we go in September, or later in the year, or early next year.
‘That depends on the clinicians and how they feel the protection has lasted for the most vulnerable groups - and, of course, virus variants that would be of concern that you would want to protect against, like for instance the South African variant.’
He added that Mr Van Tam was conducting a clinical piece of research, known as CovBoost, that would explore which vaccine would help to ‘deliver the greatest protection’ and ensure that it was available to the NHS.
The government confirmed last week that it had secured 60m extra doses of Pfizer COVID-19 vaccine for the autumn booster campaign, expected to run by GP-led teams.
People aged 40 and 41 were also invited to book their COVID-19 vaccination last week as the rollout widened to cover all of cohort 10.
Nearly three quarters of a million appointments were made on 26 and 27 April as the NHS began inviting 44-year-olds to receive jabs as GPs continue to carry out the majority of vaccinations despite workload pressures.