AstraZeneca's COVID-19 vaccine has an efficacy of 74 percent against symptomatic illness, according to the much awaited results of its large US clinical trials, which is slightly lower than the 76 percent claimed by the company back in March.

The phase 3 trial results published in the New England Journal of Medicine on Wednesday, 29 September, has also found that this efficacy goes up to 83.5 percent in the case of those over the age of 65.

In March, AstraZeneca had announced the interim results of the study saying their vaccine showed an efficacy of 79 percent. This claim was publicly contested by US health authorities after which AstraZeneca rectified it to 76 percent.

Here's what to know about AstraZeneca's US clinical trials and why it matters.

Before we look at the consequence of the trial results, let's go through some key points of the study.

• The study is being funded by the US government.

• In March AstraZeneca published the interim results of the trials, followed by the revised results after backlash from US health experts.

• This study, conducted in the US is signifiant for its large sample size.

• It began on 1st September 2020, and involves 32,451 participants.

• These participants were split into 2 groups of those who received the vaccine (21,635 participants) and those who received a placebo (10,816 participants).

What the study found

• An overall efficacy of 74 percent was established.

• In those over the age of 65, an estimated efficacy of 83.5 percent was noted.

• No severe illness or adverse events occurred in the vaccine group of participants, whereas 8 were recorded in the placebo group.

• Those who did develop symptoms mostly had mild to moderate symptoms in both groups

• However, while no deaths occurred in the vaccine group, 2 were recorded in the placebo group.

• No cases of the severe blood clot or thrombosis was reported in the vaccine group.

• The vaccine also showed an estimated 64.3 percent efficacy in preventing illness.

AstraZeneca's road to approval for its COVID vaccine, Vaxzevria, in the US has been a rocky one.

At the moment, the vaccine is not recognised in the US, the impact of which can be felt on travel and creating discrepancies in vaccine mandates within the US, where those who have been fully vaccinated with the AstraZeneca vaccine are denied entry to indoor events that require one to be vaccinated by an FDA approved vaccine.

After running into trouble with the health authorities over the interim trial results, AstraZeneca had announced back in July that it would be applying for full FDA approval rather than an EUA (Emergency Use Authorisation) which requires a closer examination and review of the data, and so will likely take longer.

Now that the company has released the results of this phase 3 clinical trials, it is likely to move the process along.