The vaccine’s manufacturer recommends an interval of at least 21 days between the first and second dose.

News of the jabs mishap emerged as Hong Kong confirmed five new imported Covid-19 cases on Thursday, taking the city’s tally to 12,025, with 212 related deaths.

The infections were identified in two arrivals from Switzerland along with three involving sea crew members from Thailand, Singapore and South Korea. Fewer than five people tested preliminary-positive for the virus.

Human Health Associates, which operates the centre where the double jab was administered, said their own initial investigation confirmed errors had been made during the inoculation, leading to the nurse being suspended from duty.

A doctor at the facility immediately reported the incident to the health department and checked on the man’s well-being, the operator added.

“Human Health is deeply concerned about the incident. After the preliminary investigation, there was a procedural error [made by] the nurse and we have relieved him of all his duties,” the spokesman said.

“We will strengthen the management and monitoring of the work of all medical staff … to ensure safety.”

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The only apparent side effect suffered by the jab recipient was a rise in blood pressure, according to media reports. The Hospital Authority said the man remained in stable condition in Tuen Mun Hospital on Thursday.

Dr David Lam Tzit-yuen, who is in charge of the inoculation centre at Queen Elizabeth Stadium, said health care workers administering the vaccine must check the patient’s HKID, provide the shot, dress the injection site, then double-check the patient’s personal information before printing their paper records.

“Medical personnel should complete all steps before walking away or moving on to the next patient … so they don’t miss any procedures or forget which step [of the process] they were at,” Lam, who is also chairman of the non-profit group Medical Conscience, told a Thursday morning radio show.

“If a person was given two Covid-19 doses at once, they could experience more significant side effects in the short term near the injection site, but it would not pose a safety threat,” Ho told the same radio show.

Ho stressed that such errors were a one-in-a-million occurrence in Hong Kong while saying he hoped medical workers would be more alert in handling vaccinations.

Dr Andrew Wong Tin-yau, an infectious disease specialist, said the older man should monitor his health to see if it remained suitable for him to get his next dose after 21 days.

“Since he got a higher dosage in his first jab [appointment], it would make sense that he may experience more side effects persisting over a longer period such as soreness at the injection site, tiredness or slight fever,” Wong said.

Wong said he believed the man should still be able to make it to his next vaccine appointment if there were no adverse reactions, explaining that another jab remained necessary to provide the booster effect that allowed antibodies to last longer.

Meanwhile, health officials announced on Thursday that ward visitation arrangements would be reinstated or expanded at 12 more specialist and acute care hospitals from August 18 for fully vaccinated individuals. The Hospital Authority said the special visiting arrangement would only apply to patients admitted for more than a week, as those staying in acute care hospitals usually had a shorter length of stay.

At present, visitation is allowed at 26 local hospitals, including some wards and departments in certain acute care hospitals.

Also on Thursday, a batch of imported fish and its packaging tested positive for the presence of the coronavirus, the first such reading in Hong Kong from the random screening of frozen or chilled food.

Authorities ordered anyone who had come into the contact with the fish sold at a stall in To Kwa Wan Market on Ma Tau Wai Road between August 10 and 12 to undergo compulsory testing, even if they have been vaccinated.