American biopharmaceutical company Pfizer has said a third dose of its Covid-19 vaccine can "strongly" boost protection against the Delta variant.Antibody levels against the Delta variant in people aged 18 to 55 who receive a third dose of the Pfizer/BioNTech vaccine are greater than five-fold than following a second dose, according to data posted at the company's teleconference, Xinhua reported.Among people aged 65 to 85, the Pfizer data suggest that antibody levels against the Delta variant after receiving a third dose are greater than 11-fold than following a second dose.Pfizer anticipates applying for emergency use authorization for a third dose of its vaccine as soon as next month, Mikael Dolsten, who leads worldwide research, development and medical for Pfizer, was quoted by CNN as saying at the teleconference.