Biotechnology company Novavax Inc (Nasdaq:NVAX ) on Wednesday announced the launch of two ongoing cross-over clinical trials of its COVID-19 vaccine candidate, NVX-CoV2373, in South Africa and the UK to ensure administration of the active vaccine to all participants.

All participants in Phase III trials in the UK and US will receive an additional round of injections. Participants will receive an additional two doses of either the vaccine (for those who originally received the placebo) or the placebo (for those who originally received the vaccine).

The company added that the participants in the South African Phase IIb study will either receive the active vaccine for those who initially received a placebo or a booster dose of the active vaccine for those who initially received the active vaccine to assess effectiveness.

In the trials in South Africa and the UK, half of the participants received the active vaccine initially, while two-thirds of the participants in PREVENT-19, the study that took place in the USA and Mexico initially received the active vaccine. The company is planning a cross-over in the PREVENT-19 study in the second quarter as well as plans to add a pediatric and adolescent arm to the study in the second quarter.

In addition, the company's UK study showed 96.4% effectiveness against the original virus strain and 89.7% overall . The South African study showed 48.6% effectiveness against a newly emerging variant of the outbreak.

Developed using Novavax's recombinant nanoparticle technology, NVX-CoV2373 is a protein-based vaccine candidate developed from the genetic sequence of SARS-CoV-2, the virus that causes the disease COVID-19.