In recent studies done by Pfizer/BioNTech, the company says they have shown that a third shot of the  Covid-19 vaccine can “strongly” boost protection against the Delta variant — adding extra protection to the standard two-dose application.

Keeping in mind that this is coming from a large pharma company,
Dr. Mikael Dolsten, who leads worldwide research, development and medical for Pfizer, called the new data on a third dose of vaccine “encouraging.”
“Receiving a third dose more than six months after vaccination, when protection may be beginning to wane, was estimated to potentially boost the neutralizing antibody titers in participants in this study to up to 100 times higher post-dose three compared to pre-dose three,” Dolsten said. “These preliminary data are very encouraging as Delta continues to spread.”
Pfizer announced it’s submitting data on the third dose of its coronavirus vaccine to the FDA as soon as next month.
But the surgeon general says not to run right out and try and get a third vaccine shot.

Surgeon general: ‘People do not need to go out and get a booster shot’