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3rd dose of Pfizer vaccine 95.6% effective against Delta, phase 3 results show

Pharmaceutical giant’s chief says trials ‘provide further evidence of the benefits of boosters’ and will be shared with regulatory agencies ‘as soon as possible’

A medical worker prepares a vial of the Pfizer coronavirus vaccine at Clalit Health Service's vaccination center in the Cinema City complex in Jerusalem, September 22, 2021. (AP Photo/Maya Alleruzzo)
A medical worker prepares a vial of the Pfizer coronavirus vaccine at Clalit Health Service's vaccination center in the Cinema City complex in Jerusalem, September 22, 2021. (AP Photo/Maya Alleruzzo)

A booster shot of the anti-COVID-19 vaccine developed by Pfizer-BioNTech is 95.6 percent effective against symptomatic infection, according to trial data published by the makers on Thursday.

The clinical phase three trial with “10,000 participants 16 years of age and older” showed “a relative vaccine efficacy of 95.6 percent against disease during a period when Delta was the prevalent strain,” the companies said in a statement.

The study presented the “first results” of a booster trial, with a third shot of the vaccine demonstrating a “favorable safety profile.”

“These results provide further evidence of the benefits of boosters as we aim to keep people well-protected against this disease,” said Pfizer CEO Albert Bourla.

The preliminary results would be shared with regulatory agencies “as soon as possible,” the companies said in the statement.

Several countries have already approved COVID-19 booster shots to increase immunity in people who have already been vaccinated but whose protection may have dipped after several months, per some studies.

In the United States, the Food and Drug Administration (FDA) approved a third dose in September for everyone aged 65 and up, as well as people at high risk of developing severe COVID.

Used vials of the Pfizer-BioNTech COVID-19 vaccine lay empty at a vaccination center at the University of Nevada in Las Vegas, January 22, 2021. (AP Photo/John Locher, File)

The European Medicines Agency (EMA) approved a booster for over-18s at the beginning of October, allowing national regulators to decide which groups should be eligible first.

In Israel, authorities have gone further, approving booster shots for everyone aged 12 and over.

Some in Israel had initially feared that the vaccine was less effective against the Delta mutation as a sharp spike in cases over the summer coincided with the variant reaching the country. However, Israeli researchers have since concluded that fading immunity from the initial doses of the shot was responsible, launching a massive booster immunization campaign.

Israeli officials have raised concerns in recent days about the arrival of a new subvariant called AY4.2. On Wednesday, Prime Minister Naftali Bennett ordered that the new strain be closely monitored, after meeting with top health officials.

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