The US FDA has released a review of Pfizer's application seeking approval for booster shots of its COVID-19 vaccine on Thursday, 16 September.

Pfizer had approached the US FDA in July seeking approval for a third booster dose of their COVID-19 vaccine citing the mounting threat of the Delta variant and how it has been established that the vaccines are less effective against the variant, especially after a period of time.

An advisory of experts is said to meet and take the final recommendation on approving Pfizer's request, reported the New York Times.

Although COVID-19 booster shot have been authorised by the US FDA for immunocompromised and elderly people, the FDA has expressed time and again that considering the safety and efficacy data available, they don't see a need for a third booster dose for everyone just yet.

A number of experts and health authorities including the WHO stand by this position, with Director-General Tedros Adhanom Ghebreyesus asking for a moratorium on booster shots.

Let's break down what the US FDA review says.

The data presented by Pfizer to make their case is from a study conducted by the company on 300 adults who received a third dose of their COVID vaccine 6 months after they were fully vaccinated.

On reviewing the data, the regulators found,

1. The participants elicited a higher immune response after the booster dose.

2. No particular safety issues were noted.

3. The initial two doses are still effective in preventing serious illness.

It has been noted, however that this study is a rather small one, although Pfizer is confident that it is enough to make their point for the time being, according to the New York Times.

The company reportedly has another, larger study underway.

The booster doses, basically aim to reduce infections altogether, unlike the first two doses whose main goal was to prevent severe illness and death.

Pfizer cites other studies particularly the ones from Israel to make it's case about vaccine efficacy diminishing over time, saying "vaccine protection against COVID-19 infection wanes approximately 6 to 8 months following the second dose". They reiterate that a booster dose is required to prevent the surge of breakthrough infections of Delta.

The FDA, from it's review doesn't seem entirely convinced by the data, refusing to take a stance just yet. A final reccomendation is expected to come from an external advisory by the end of this week.

The Biden administration parallelly has announced that it aims to roll out booser shots for everyone over the age of 16 by 20 September, reported NPR.

(Written with inputs from the New York Times and NPR.)