DUBAI — A "very small number" of people in the United Arab Emirates are being invited to receive a third shot of the Sinopharm coronavirus vaccine after antibody tests indicated they did not have a sufficient immune response following two doses of the Chinese-made vaccine, its distributor confirmed Sunday.

There have also been reports out of China of people being initially unresponsive to the vaccine and requiring additional doses.

Walid Zaher, the chief researcher for G42 Healthcare, which distributes the Sinopharm vaccine in the UAE, told Dubai Eye radio that a study was underway to give some people third doses.

“When some people are found to be not really responsive to the vaccines, which is expected with all vaccines, there was an initiative to approach these people and give them a third shot of the Sinopharm vaccine, which has shown, within the context of the study, to boost their immunity,” he said.

Zaher said anyone with low levels of antibodies after a test could ask their doctor to contact health authorities and an appointment would be made for them to have another dose, but generally it’s the officials that approach the person.

He likened the third shot to a flu booster shot and said the amount of people who need it is a “very small number.” The need for a third shot was first mentioned March 10 to the National newspaper by the spokeswoman for the country’s health sector, Farida al-Hosani.

Doctors told the Wall Street Journal there were cases of people with little or no antibody response after two doses of Sinopharm.

The revelations could raise doubts about the effectiveness of the vaccine, which is being widely used around the world as countries scramble to inoculate their populations. Many of the more effective Western-made vaccines have been snapped up by wealthier nations.

The Sinopharm vaccine has a self-reported efficacy rate of 79 percent, which global health experts say is more than adequate, but its data has not been publicly released. In addition to the UAE, the vaccine has been purchased by countries such as Egypt, Cambodia, Senegal and Peru.

In China, over the weekend, medical authorities also announced that a clinical pathologist had become infected with the coronavirus despite being vaccinated weeks earlier. They did not specify which vaccine she had used, but her facility is known to administer the Sinopharm one.

“Perhaps she needs to get a third shot as the two doses of inactivated vaccine had failed to create enough antibodies in her,” Gao Fu, director of the Chinese Center for Disease Control and Prevention, told state broadcaster China Central Television on Saturday. “Or she is one of the few who happen to be unresponsive to the vaccine.”

The UAE has distinguished itself with an aggressive vaccination program that initially used Sinopharm, which conducted Phase 3 trials in the country, and was later expanded to include Pfizer-BioNTech, AstraZeneca and Russia’s Sputnik V.

Nearly 73 percent of the elderly population and 56 percent of all adults have received at least one vaccine dose, authorities said Saturday.

As of Sunday, everyone in the country is eligible for a vaccine, authorities said, after restricting injections for the past six weeks to those with special needs.

The UAE has the second-highest national vaccination rate in the region after Israel, with more than 7 million doses given to a population of 9 million. The vaccine is free to all citizens and residents.

The UAE saw an explosion of new coronavirus infections in January after tourists from all over the world flocked to Dubai, which had marketed itself as a restriction-free holiday destination.

The number of new daily cases quadrupled to nearly 4,000 in January and only now has dropped down to about 2,000 new cases a day.

Lyric Li in Seoul contributed to this report.