Israel has started administering a booster shot of Pfizer's Covid-19 vaccine to people with weak immune systems, the media reported. It is one of the first countries to globally approve a booster shot.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 Health Ministry will offer the third jab to immunocompromised patients, such as recipients of organ transplants, the Wall Street Journal reported.This is following evidence that the booster shot may increase such patients' antibody counts, according to a Health Ministry letter sent to Israeli healthcare providers, the report said.The Ministry said the recommended time between a second and third shot would be eight weeks, with a minimum gap of four weeks.While the booster shots are not yet rolled out for the general public, the government is, however, weighing the option.Israel is trying to halt a new outbreak of the Delta variant and has launched a campaign calling teenagers over 12 years old to get vaccinated.Although most reported cases have been mild or asymptomatic, there has been a steady rise in the number of infections.On July 11, Israel also signed a deal with Pfizer to receive a new batch of Covid-19 vaccines in August.In a statement at the start of the weekly cabinet meeting, Prime Minister Naftali Bennett said that "last night we closed a deal to bring forward the next shipment of vaccines to August 1", reports Xinhua news agency.He said that together with existing vaccine stocks, the new batch will ensure "from this moment, a continuous inventory of vaccines in Israel".Meanwhile, the US Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA), last week, 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.