New York, Sep 13 : US-based pharmaceutical major Pfizer and German biotech firm BioNTech have announced to expand the enrollment of their Phase 3 Covid-19 vaccine trial to up to approximately 44,000 participants, up from an initial recruitment goal of 30,000 individuals. The companies said a conclusive result on the efficacy of the vaccine is likely by the end of October. "Enrollment in the trial has been proceeding as planned and the companies expect to reach its initial target of up to 30,000 participants next week", they said in a joint statement on Saturday. The expansion would allow the companies to further increase trial population diversity, and include adolescents as young as 16 years of age and people with chronic, stable HIV, Hepatitis C, or Hepatitis B infection, as well as provide additional safety and efficacy data. The US Food and Drug Administration (FDA) will have to approve the change in the Phase 3 Covid-19 vaccine trial before it goes into effect. The Pfizer and BioNTech study is likely to be among the first in the US to report efficacy data from a Phase 3 trial. In August, the companies announced positive results for the Phase 1 trial of their second Covid-19 vaccine candidate called BNT162b2 or B2, revealing that the latest vaccine candidate has fewer side effects than their first. The vaccine uses mRNA -- the genetic messenger the body uses to make the DNA code into proteins -- packaged inside a fatty capsule, called a lipid nanoparticle, that allows it to get into cells. Several vaccines have already begun phase 3 clinical trials in the US, including vaccine candidate AZD1222, co-invented by the University of Oxford and its spin-out company Vaccitech, vaccine candidate mRNA-1273, developed by the US National Institute of Allergy and Infectious Diseases (NIAID) and American biotechnology company Moderna, and vaccine candidate BNT162b2 or B2, developed by Pfizer/BioNTech. /IANS