Medical workers prepare an oxygen parlor for COVID-19 patients in Kolkata, India, May 3, 2021. Photo: Xinhua

Pfizer COVID-19 vaccines have been dragged into the spotlight over efficacy concerns against the new double mutant variant first found in India after an infectious disease specialist from the US, who had received two Pfizer shots prior to his arrival in India, passed away after testing positive for coronavirus at the age of 81, local media reported on Wednesday. 

Although there is no direct evidence showing reduced efficacy of Pfizer vaccines against the new mutated strain, previous studies suggest a reduced protection rate against other variants, health experts reached by the Global Times said.

Dr Rajendra Kapila, a professor at Rutgers University in Newark, New Jersey specializing in infectious diseases, arrived in India in late March and was scheduled to fly back to the US in mid-April, but he found he was infected with COVID-19 on April 8 and was later admitted to Delhi's Shanti Mukund Hospital, local media the Hindustan Times reported on Wednesday. 

He died at the hospital on April 28, the report said, but no details on the cause of his death have been disclosed, nor has it been specified if Kapila was infected with the double mutated virus. 

"For the last one year I have been working at a COVID-19 lab in New Jersey and had ensured a safe environment at home," said Dr Deepti, Kapila's wife who traveled with him to India. "It is ironic that we came to India for two weeks and he contracted it here," she said, Hindustan Times reported.

Mainstream Western media have stayed silent on Kapila's death, and the Shanti Mukund Hospital did not reply to the Global Times' inquiry as of press time.

However, reports have been circulating on social media such as Reddit since May, which said that Kapila had died from undisclosed complications of COVID-19. A Facebook user named Neha Majmudar, who claimed he had been given consent from a family friend of Kapila, replied under a post that "Kapila had history of diabetes and CAD S/P stents… and passed away following a massive heart attack in the early morning hours." But this information cannot be verified so far.  

People wait to receive COVID-19 vaccination at a government school in Delhi, India, on May 3, 2021. (Xinhua/Partha Sarkar)

India's National Institute of Virology shared limited data on the double mutant virus strain in April, which showed that of the 361 genome-sequenced samples collected between January and March this year, 220 of them - almost 61 percent - had carried the double mutation, Indian Express reported. 

In another article, the Indian Express said that the strain, also known as the B.1.617 variant, is fast replacing the previous variant in south India and is becoming dominant, according to scientists at a local Indian research center on Tuesday. 

Tao Lina, a Shanghai-based vaccine expert, told the Global Times on Wednesday there is no direct evidence showing whether the Pfizer vaccine is effective on this variant or not, while noting that China-developed inactivated vaccines might be more effective against the double mutant than mRNA ones.

"Technically, Pfizer vaccine uses human cells to synthesize S protein in the human body to produce antibodies, whereas China-developed vaccines, including Sinovac and Sinopharm, use inactivated viruses as antibodies, which may cover more variants than Pfizer does," Tao said.  

Tao added that while the efficacy of Pfizer against the new double mutant remains unknown, previous medical studies suggested a reduced efficacy rate of Pfizer shots against other COVID-19 variants.

"The human body develops resistance to vaccines, and the variants may need even five or six doses of vaccine instead of merely two to produce enough protection," he noted.

Chinese experts also warned that seniors, people who are obese and those with chronic diseases may have a reduced response to vaccines, while urging India to conduct further research on Kapila's case. 

According to the World Health Organization on Wednesday, over the past week India accounted for nearly half, or 46 percent, of the world's total COVID-19 infections, and a quarter of global death toll. 

According to a press release on its official website, Pfizer said its vaccines show a 95.3 percent efficacy rate against severe COVID-19 cases, which has been defined by the US Food and Drug Administration.