Fourth COVID Shot Boosts Protection Fivefold, Israeli Study Suggests

A second COVID booster shot, administered to more than 25,000 Israelis, produces a five-fold increase in the level of antibodies, the Sheba Medical Center reports

Ido Efrati
Ido Efrati
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A medical worker at Sheba Medical Center receives the fourth dose of the vaccine on December 28, 2021.
A medical worker at Sheba Medical Center receives the fourth dose of the vaccine on December 28, 2021.Credit: Gil Cohen-Magen
Ido Efrati
Ido Efrati

Preliminary findings from an Israeli study of the effects of a fourth COVID vaccine dose indicate it produces a fivefold increase in the level of antibodies.

The Sheba Medical Center, outside Tel Aviv, reported on Tuesday that the increase was seen a week following the inoculation with a second booster shot, which Israel began administering amid a surge in omicron infections.

The study, which is focused on the safety and effectiveness of a fourth dose, began last week on 154 employees of the medical center. They had all received their first booster shots no later than August 20 of last year and had antibody blood test readings under 700. All the participants in the trial have been undergoing blood testing to track their level of antibodies.

In a visit to the Sheba Medical Center earlier on Tuesady, Prime Minister Naftali Bennett said: “A week into the fourth dose we know to a higher degree of certainty that the fourth dose is safe."

The initial findings "most likely mean a significant increase against infection and …hospitalization and (severe) symptoms,” he added.

Prof. Gili Regev-Yochay, the director of infection prevention unit at Sheba, who also directed the study, said, “These preliminary findings are in addition to preliminary results received on side effects following the fourth dose and also indicate the safety of the fourth dose. This study will produce additional information in the days and weeks to come.”

The preliminary findings on the safety of the fourth dose were published last week and showed results similar to those from the first booster shot, the third dose.

The new findings show that about 80 percent of the participants in the study reported a minor localized reaction to the vaccination. About 45 percent reported symptoms such as weakness, muscle aches or a headache. Ten percent reported a fever that in most cases subsided within a day.

Regev-Yochay explained that it appears at this stage that the fourth does is as safe as the prior three.

Two weeks ago, Israel's pandemic advisory panel recommended administering a fourth dose of the coronavirus vaccine to vulnerable people on the basis of partial data which revealed a significant waning in protection provided by the booster shot after a few months. 

Researchers advising the panel presented a preliminary analysis depicting eroding immunity provided by the third vaccine against delta among those 60 and over, with protection waning as soon as after three months. 

A graph of the number of infections per 100,000 risk-days (meaning days of potential exposure to the virus) among those 60 and over revealed that in the first month after receiving the third dose, there were two cases of infection. By the fifth month, there were on average more than five infections per 100,000 risk-days.

The figures show that the third dose, the booster shot, provided a high level of protection – four times that of the second dose. But the presentation to the committee also included the following: “The noted protection against inflection with the delta variant for those vaccinated with the booster begins to erode.” 

Due to the decline in the booster's efficacy, Prime Minister Bennett on Sunday urged older Israelis to get a fourth coronavirus shot in a nationwide address, after announcing the Health Ministry's approval of a fourth shot for all adults aged 60 and over as well as medical staffers.

Around 25,000 people were vaccinated on Monday following the announcement, and another 100,000 people have already made appointments to receive their fourth dose.

There are over 800,000 people aged over 60 who received the booster dose more than four months ago, and they are three times more likely to get infected with coronavirus than people who just received the vaccine. The data also showed that there was a significant decrease in protection for elderly people who received the inoculation three months ago.

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