Drug manufacturer AstraZeneca on Thursday said it may conduct an additional study to validate concerns amid concerns over the efficacy of its vaccine.

The statement came after AstraZeneca and Oxford University acknowledged a manufacturing error that raised questions about preliminary results of the vaccine candidate. The problems in the drug’s efficacy that could arise due to this error is still unclear.

In an interview to Bloomberg, AstraZeneca’s Chief Executive Officer Pascal Soriot, in his first interview since data on its trial was published, said: “Now that we’ve found what looks like a better efficacy we have to validate this, so we need to do an additional study.” He said that it will probably be another international study, but this one could be done faster as they were now aware of the efficacy being high so a smaller number of patients will be needed.

Soriot also said he did not expect the additional trial to abide by approvals in the United Kingdom and the European Union.

The British government had on Friday said it has formally asked its drug regulator to assess whether the Oxford coronavirus vaccine should be authorised for use. United Kingdom’s Matt Hancock said he had asked the Medicines and Healthcare Products Regulatory Agency to establish whether the vaccine “meets rigorous safety standards”, reported AP.

The United Kingdom’s decision came amid questions about the vaccine candidate’s efficacy. The Boris Johnson-led government has ordered 100 million doses of the Oxford-AstraZeneca vaccine, and has planned to start distributing it in December after approval.

Though the problems in the drug’s efficacy that could arise due to this error is still unclear, experts said that a relatively small number in the low dose group will make it difficult to ascertain the actual efficacy of the vaccine candidate or a statistical anomaly.

A group of volunteers in the AstraZeneca trial received a lower dose of the vaccine candidate than the others who got two full doses. In the lower dose group, AstraZeneca said that the vaccine appeared to be 90% effective. For those who took two full doses, the vaccine was just 62% effective. In combination, the vaccine turned out to be 70% effective, the drug maker said.

AstraZeneca on Monday said that its potential coronavirus vaccine, which is being developed with Oxford University, has shown more than 70% overall efficacy in a third phase interim trial.

Serum Institute of India on Thursday said that the potential coronavirus vaccine being developed by pharmaceutical company AstraZeneca and the Oxford University is “safe and effective” and that the Indian trials are progressing smoothly with strict adherence to all protocols.