The U.K. government is facing questions over whether the country is about to face a shortage in the supply of coronavirus vaccines, a factor that could dent its so-far successful immunization program.

“We have less supply than we might have hoped for the coming weeks but we expect it to increase again later,” Housing Secretary Robert Jenrick told the BBC on Thursday.

“The vaccine rollout will be slightly slower than we might have hoped but not slower than the target,” he said. “We have every reason to believe that supply will increase in the months of May, June and July.”

Later, Jenrick told Sky News that the government is “sourcing vaccines from all over the world and we are experiencing occasionally some issues and that’s led to this, this issue with some supply in the coming weeks.”

Jenrick’s comments come amid a flurry of reports in the British media that the U.K.’s rollout could be about to hit some turbulence. It’s been widely reported that a delivery of millions of doses of the Oxford-AstraZeneca shot being produced by the Serum Institute of India could be held up by four weeks.

Jenrick refused to comment on specific contracts, however. CNBC has contacted the Serum Institute of India, the world’s largest vaccine manufacturer, for comment on the reports but is yet to receive a reply.

Ten million doses of the AstraZeneca Covid vaccine were expected to come from the SII, Reuters reported in early March. In all, the U.K. has ordered 100 million doses of the AstraZeneca-Oxford vaccine, with the bulk of the supply coming from within the U.K.

However, Britain is also facing possible disruptions to supply if the EU goes through with a proposal to withhold exports of vaccines made in the bloc while its own program lags. Supplies of the Pfizer-BioNTech vaccine that the U.K. is also using in its vaccination program come from Belgium.

Since it began its rollout started in December, Britain’s health service has overseen the vaccination of over 25 million people with a first dose of the vaccine. Over 1.7 million people have now had a second dose of the two-shot vaccines currently being used in the U.K., government data shows.

‘Still on track’
The National Health Service had reportedly already warned of a reduction in supply for England “in April in a letter to local health organizations,” according to the BBC.

But the government has said that it is still on track to offer all over-50s a first dose of the vaccine by April 15, and all U.K. adults a first shot by the end of July.

“The vaccination programme will continue in the coming weeks and more people will continue to receive first and second doses,” a Department of Health and Social Care spokesperson said in a statement Wednesday night.

“As has been the case since the programme began, the number of vaccinations carried out over time will vary due to supply.”