AstraZeneca boss not yet sure if booster shots will be needed

In remarks to CNBC, the drug giant's chief executive officer, Pascal Soriot, said that Astra did not have a "precise answer".

While the antibodies in the human body triggered by a vaccine did tend to decline over time, T-cells, which were also activated by the shot tended to be durable.

"We know that [our vaccine] has a decline of antibodies [over time] — we haven’t seen yet a decline of efficacy but it’s a bit early to judge, only time will tell, and I hope the T-cells will provide this durable, long-term protection," he reportedly said.

T-cells also protect against severe Covid-19.

The day before, Pfizer boss, Albert Bourla, had argued in favour of administering a third vaccine dose, or booster shot, saying the company was "very, very confident" that it would protect against the Delta variant of Covid-19.

Previously, a study published by Pfizer and BioNTech showed that the effectiveness of their vaccine declined by approximately 6% every two months and Bourla told CNBC that the efficacy dropped to 84% between four to six months after giving the second dose.