The Health Ministry on Sunday alerted health providers and clinics to not administer a third Covid vaccine booster shot to most patients undergoing cancer treatment, The Times of Israel reported.
Last week, the country, one of the first countries to globally approve a booster shot, began administering third vaccine doses to people with weakened immune systems, including organ transplant recipients and those with autoimmune diseases.
Cancer patients are also sometimes immunocompromised.
About 90 per cent of cancer patients who were vaccinated and undergoing chemotherapy for solid tumours "maintained a high level of antibodies following the vaccine" and thus there was no immediate need for a booster, according to a statement from the Mnistry.
Further, the vaccine may cause side effects in some patients, including "lymph node enlargement or liver dysfunction", and therefore "the recommendation at this time" is not to administer a third Covid dose to cancer patients, it added.
While most cancer patients were exempt from a third dose, the ministry noted that those with certain hematological cancers include patients with chronic lymphocytic leukemia; multiple myeloma; and non-Hodgkin's lymphoma should take the booster jab, but in consultation with a physician, the report said.
The list of people eligible for a third dose of the Covid vaccine also includes heart, lung, kidney and liver transplant recipients; those with multiple sclerosis; and patients with rheumatological or autoimmune diseases, Emilia Anis, head of the Ministry's epidemiological unit, was quoted as saying.
However, all these must consult a physician before the jab.
The Ministry also recommended an antibody test prior to receiving the shot and another 14 days later "to assess the benefits".
The decision for the third jab comes as Israel is witnessing an outbreak of the highly contagious Delta variant, after being one of the first to fully inoculate more than 60 per cent of adults in the country.
The booster rollout last week, was following evidence that the booster shot may increase such patients' antibody counts.
Meanwhile, the US Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA), have recently released a joint statement on vaccine boosters, saying that people who are fully vaccinated are protected from severe illness and death, including from emerging variants such as the highly contagious Delta variant.
"FDA, CDC, and NIH (National Institutes of Health) are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary," said the statement.
Israel has also signed a deal with Pfizer to receive a new batch of Covid-19 vaccines in August.