A resident of Korian Les Amandiers EHPAD (Housing Establishment for Dependant Elderly People) receives a dose of the Pfizer-BioNTech COVID-19 vaccine during a vaccination campaign to fight against the spread of COVID-19 in Paris, France, Jan. 7, 2021.Photo:Xinhua

Concerns over the mRNA vaccine intensified following a Russia Today report on Monday that all 78 residents at a nursing home in Madrid, Spain had tested positive for COVID-19 after being given their first dose of the Pfizer-BioNTech vaccine on January 13, and at least seven people have died.

A Chinese virologist advised elderly people, especially those with underlying conditions, not to take mRNA vaccine such as Pfizer's, as it could induce their condition and worsen their health, while a vaccine expert warned the public to take appropriate measures even after being vaccinated, as people are likely to be infected with the virus before the vaccine takes effect. 

Most of those who succumbed to the virus had pre-existing conditions, according to Spanish news agency EFE, while four residents are hospitalized, and 12 staff members have also been infected, Russia Today reported.

The report didn't say whether the deaths and cases testing positive are directly linked to vaccination. 

Yang Zhanqiu, deputy director of the pathogen biology department at Wuhan University, told the Global Times on Tuesday that the positive test for COVID-19 can be divided into two cases: one is antibody positive and another is positive nucleic acid testing. 

He noted that the positive nucleic acid testing result is "highly unlikely." Yang explained that the vaccine could not been approved until it passes safety tests, so it will not work like a "synthetic virus" infecting humans.

A normal person whose antibody is positive after taking the mRNA-based vaccine suggested that he/she got protected from getting infected, Yang said. 

He explained that the mRNA vaccines teach human cells to make a protein to trigger an immune response, which can then protect people from getting infected if the real virus enters the body.

Tao Lina, a Shanghai-based expert on vaccines, told the Global Times that it is possible that the vaccination causes positive IgM antibodies, which is a natural process. IgM is usually the first antibody produced by the immune system when a virus attacks. 

In this case, the seven could have died of other illnesses. Tao urged an immediate investigation into their deaths. 

But if the 78 people were positive for the nuclei acid test, it would suggest that they were infected with the coronavirus before being vaccinated, or before the vaccine took effect, Tao said. 

The infected patients could have failed to take appropriate measures against the virus, Tao noted. 

Yang warned that, unlike inactivated vaccines, the use of mRNA-based vaccines carries the risk of causing abnormal immune dysfunction, allergy or even death especially among the elderly and people with underlying diseases. 

Some components in mRNA vaccines, such as polyethylene glycol, have not been used in vaccine production before, and the mRNA-based vaccine was first approved to treat an infectious disease amid this COVID-19 pandemic, so Yang suggested elderly citizens and people with underlying conditions not to take the vaccine. 

The reports of deaths and cases testing positive following vaccination in Spain were not the first.  

In mid-January, Norway reported the deaths of 23 elderly Norwegian people who received mRNA-based COVID-19 vaccines. All the deaths occurred in frail, elderly patients in nursing homes. All were over 80 years old and some of them over 90, Norwegian media NRK reported.

More than 12,400 people in Israel had tested positive for coronavirus after being vaccinated with Pfizer's COVID-19 vaccine, including 69 who had received their second dose, media reported in January.