Professor of immunology at the Technion says 4th jab with the same vaccine and the same antigens can make it more difficult for body to respond to new variants, causing harm in the end

Amid its fifth wave of infection, Israel has become the first country in the world to widely disseminate a fourth jab of the coronavirus vaccine.

But some experts caution that administering vaccines too often could reduce the immune system’s ability to cope with future variants.

ליברמן מתחסן בחיסון הרביעי
Finance Minister Avigdor Liberman receives his 4th coronavirus jab


On January 2, Israeli Prime Minister Naftali Bennett said the country would start administering a fourth dose of the coronavirus vaccine to residents who are at high risk of severe illness or death from COVID-19, including health care workers and those who are age 60 and older. A fourth dose had already been approved for immunocompromised individuals.

The Health Ministry, on its website, said that due to the spread of the omicron variant and studies showing there has been a decline in protection even among fully vaccinated individuals, the ministry’s director-general had “accepted the experts’ recommendation to administer the fourth dose for those at highest risk for severe illness and death.”

מיכל הרצוג
First Lady Michal Herzog receives her fourth vaccine in Jerusalem (Pיםאם: GPO)


But the experts are not unanimous in viewing the fourth vaccine as a good idea.

Doron Melamed, a professor of immunology at the Technion – Israel Institute of Technology in Haifa, explained why too many doses of the vaccine could cause immune system fatigue.

“When you’re exposed to a vaccine, during the immune response, the immune system generates very highly specialized and specific cells that are called memory cells. But at the same time, they maintain a flexible compartment of cells that can modify their specificity.”

Professor Melamed pointed out that viruses constantly mutate and evolve; they don’t return year after year unchanged. “As with influenza, every year we see a different virus.”

“It is very important that the flexible compartment be maintained,” Melamed said, because this provides the most efficient response to the virus as it mutates.

חיסון קורונה בנתניה
The coronavirus vaccine (Photo: AFP)


When we immunize people for the fourth time with the same vaccine and the same antigens, he said, we strengthen the immune system’s highly specific cells at the expense of the flexible ones. This can lead to a situation in which it is much more difficult to respond to new variants; the immune system has become so highly specialized that it has lost its flexibility.

Professor Melamed said that while this theory explaining immune system fatigue is not universally accepted, it is becoming increasingly popular among epidemiologists around the world who conclude that “highly repeated vaccination may be harmful in the end.”

“There are vaccines that we get once in a lifetime, and there are vaccines that we need to get every five years,” the professor said. The appropriate schedule for the COVID-19 vaccine is “something that needs to be measured.”

Melamed charges that “the Israeli government is not taking into consideration any opinions given by immunologists. They are biased toward physicians and others who are not immunologists.”

Professor Ronit Calderon-Margalit, an epidemiologist at Hadassah Medical Center and a lecturer in the Hebrew University of Jerusalem, said that there is not yet enough information on whether the fourth shot will help stop the virus from spreading. “I think the decision to administer it was based on the success of the past shots from preventing the spread,” she said.

חיסון קורונה בתל אביב
Nurse prepares to administer the coronavirus vaccine in Tel Aviv (Photo: AFP)


“We earned some time – a few weeks – by closing the borders before omicron started spreading around,” Calderon-Margalit said, “and I think it would have been a good choice to use that time to conduct studies on the fourth shot.”

Given that this shot has been already provided to certain citizens, she believes “it is the responsibility of the government to continue to observe those who received the fourth shot.”

Calderon-Margalit added that it would be much more effective “to invest efforts in vaccinating those who did not receive the first three shots rather administer the fourth shot to people who already had the first three.” This, however, would require a much greater effort, since those who did not receive the first three shots are apparently inclined to not get vaccinated at all.

The professor concluded: “We would gain more by vaccinating them than we do by investing in a fourth vaccine campaign.”

As reported by Ynetnews