A panel of Israeli health experts has recommended offering a fourth dose of coronavirus vaccine to all adults age 18 and over.

The shot would be administered only to those who received the vaccine at least five months earlier or recovered from coronavirus at least five months before, the Health Ministry said in a text message. The ministry’s director-general, Nachman Ash, would have to approve the recommendation for it to go into effect.

The recommendation was made after a ministry study showed that the fourth dose provided three to five times more protection against serious illness, and twice as much protection against infection than just a third dose. Israel began administering a fourth inoculation to the immunocompromised and people 60 and over earlier this month.

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Infectious disease specialist Eyal Leshem of Sheba Medical Center questioned the ministry’s findings, saying the people who chose to have the fourth dose may also be more likely to avoid risky exposure to infection, skewing the results of the comparison.

While a fourth dose may be a good idea for senior citizens or those who suffer from chronic illness, it isn’t necessary for younger adults, Leshem said. The vaccines could be put to better use in countries where inoculation rates are low, he said.

“Three doses of the vaccine provide excellent protection against severe disease for young and healthy people, and the added value for a fourth dose is currently unknown and not expected to be substantial,” he said. “From a global perspective, use of multiple boosters in low-risk populations during a short period should be weighed against the global shortage of COVID vaccines.”