SINGAPORE - As at 4.30pm on Monday (Oct 25), 86 out of the 117 people who had received the wrong dose of Covid-19 vaccine at Bukit Merah Polyclinic have received their replacement dose, SingHealth Polyclinics' chief executive Adrian Ee told The Straits Times.

SingHealth Polyclinics had said on Sunday that an error in administering the vaccine resulted in six staff and 111 patients receiving a much lower dose - about one-tenth - of the Covid-19 vaccine.

It added that based on the current vaccination guidelines by the Ministry of Health, the initial reduced dose was unlikely to cause any adverse reactions, and it would be clinically safe for those affected to get a replacement dose of the vaccine.

Checks showed that Bukit Merah Polyclinic only offers the Pfizer-BioNTech/Comirnaty vaccine.

The error, which was discovered on the evening of Oct 22, was the result of a mistake in identifying the markings on new syringes.

Dr Ee said on Monday that the new syringes had been introduced to the clinic on Oct 20.

The patients were given the wrong doses from Oct 20 to 22.

No further details were given on why the new syringes were being used, what safeguards were in place at the time of the incident, or whether other polyclinics were using the same type of syringe.

"Immediate steps were taken to rectify the error, and staff have been reminded on the proper use of the new syringe to administer the Covid-19 vaccine," said Dr Ee.

He added that all the affected patients have been contacted and arrangements have been made for them to receive their replacement doses as soon as possible.

Dr Ee said that processes have been thoroughly reviewed since the incident, which is an isolated one.

He added that all other vaccinations and services at SingHealth's polyclinics have not been affected, and that all patients who visited Bukit Merah Polyclinic for their Covid-19 vaccinations on other days are not affected by this incident.

Dr Ee added: "Following the incident, we have thoroughly reviewed our processes, and will ensure that staff are familiar with the use of new devices to prevent another recurrence in our polyclinics."

This is not the first time patients have been given the wrong dosage of the Covid-19 vaccine in Singapore.

In January this year, a staff member at the Singapore National Eye Centre was mistakenly given the equivalent of five doses of the Pfizer-BioNTech Covid-19 vaccine.

The worker in charge of diluting the vaccine had been called away to attend to other matters before it was done.

A second staff member then mistakenly believed the undiluted dose in the vial was ready for administering.

In June, a 16-year-old boy was wrongly given the first dose of the Moderna Covid-19 vaccine, which has not been approved for those under age 18 in Singapore.

The mistake was discovered at Kolam Ayer Community Club vaccination centre when its staff realised that the boy was under 18 years of age after he had been given the shot.