A staff member at the Singapore National Eye Centre (SNEC) has been mistakenly given the equivalent of five doses of the Pfizer-BioNTech Covid-19 vaccine.
This occurred during a vaccination exercise on Jan 14, and was due to human error resulting from a lapse in communication among members of the vaccination team, said SNEC yesterday. It said it has been following up closely with the staff member, who remains well.
SNEC said 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 had then mistaken the undiluted dose in the vial to be ready for administering.
The error was discovered within minutes after the vaccination.
"Senior doctors were alerted immediately and the staff (member) was assessed and found to be well, with no adverse reaction or side effects," said SNEC.
The worker was warded at the Singapore General Hospital (SGH) for further observation, before being discharged two days later.
As a safety measure, the vaccination exercise at SNEC was stopped immediately upon detection of the error, and the rest of the staff were vaccinated at SGH.
The centre is not involved in the vaccination of other groups.
The SNEC has apologised to the affected staff member and the worker's family, said Professor Wong Tien Yin, the medical director of the centre. "SNEC takes a very serious view of this incident. The safety of those receiving the vaccination during our staff vaccination exercise is of our utmost priority," he added.
He said that the centre has done a thorough review of its internal processes, and taken steps to tighten them so that such lapses do not occur again.
SNEC told The Sunday Times that the worker involved in administering the vaccine injection has been counselled.
Yesterday, the Ministry of Health (MOH) said it has worked with SNEC to identify the lapses which contributed to the error.
"Clinical trial data from Pfizer-BioNTech has indicated that receiving more than the recommended dose of the Pfizer-BioNTech Covid-19 vaccine is unlikely to be harmful," said the ministry. It said it has not been notified of any similar incidents at other vaccination sites.
MOH also said there are robust medical protocols in place at all vaccination sites to ensure the safety of those vaccinated.
"These include protocols for vaccination processes on dose preparation, dilution and vaccine administration, including the need for clear indication to differentiate diluted and undiluted vaccine vials," it said.
The ministry said it has since reminded vaccination providers to adhere strictly to the protocols, and will continue to work with them to ensure the utmost safety in the vaccination process.
Infectious diseases experts that The Sunday Times spoke to also said the overdose is unlikely to be harmful. Some noted a similar case in Germany last year, where eight workers in an elderly home received a vaccine overdose but did not show any severe adverse effects.
It will also not cause the worker to get Covid-19, said Professor Ooi Eng Eong of the Duke-NUS Medical School.
But the overdose might amplify the common side effects of the vaccine, such as fever and aches.
Some experts also said the staff member would still require a second dose of the vaccine.
A system where at least two people check that the correct dose is being administered should be in place, said Dr Leong Hoe Nam from Mount Elizabeth Novena Hospital.
Associate Professor Hsu Li Yang of the NUS Saw Swee Hock School of Public Health said mistakes made during the vaccination drive are "inevitable in some way", but cases of overdosing should be extremely rare now that the incident has been highlighted.
"Ultimately, however, errors are reduced by practice and familiarity with procedures," said Professor Paul Tambyah, president of the Asia-Pacific Society of Clinical Microbiology and Infection.
He said the chances of error are likely to drop significantly once primary care providers such as general practitioners are tasked to do it, as they would be more experienced in administering vaccines.
As at last Tuesday, more than 175,000 people had received their first dose of the vaccine. About 6,000 people have also taken their second and final dose.