CAJICA, Colombia – Following the start of phase III trials for its COVID-19 vaccine, Soberana 02, Cuban researchers have started phase III trials for Abdala (CIGB-66), another vaccine candidate developed in the island country.

“Abdala is a subunit vaccine based on the receptor-binding domain (RBD) of the SARS-CoV-2 protein S,” Amilcar Pérez-Riverol, a Cuban postdoctoral researcher at the Sao Paulo Research Foundation (FAPEPS) at Sao Paulo State University in Brazil, told BioWorld. “This platform is one of those that has been used to obtain vaccines for COVID-19.”

Abdala is being developed by Cuba’s Center for Genetic Engineering and Biotechnology (CIGB). The Cuban government says 48,000 doses of the first of three shots of the jab were administered to members of CIGB and health care workers in the country, reaching the whole target of participants proposed for the trial. Abdala is designed to be administered three times, every 14 days.

Three different COVID-19 vaccines have been developed in Cuba, and two have made it to phase III trials in the country, although no papers have been published about preclinical trial results from either Soberana 02 or Abdala.

Preprints on the Abdala vaccine candidate have not been published either, and there is little information available about the technology behind these vaccines, beyond what the state-controlled media has published.

“All three [Cuban vaccine candidates] are RBD-based subunit vaccines,” explained Pérez-Riverol, who has been closely following the development of Cuban vaccines. “The difference is that the RBD used in Soberana 01 and 02 is produced by recombinant DNA technology in mammalian cells (CHO), while that of Abdala is produced in yeast cells.”

According to Pérez-Riverol, the CIGB in Havana has long experience in vaccine research and it is thanks to that experience that the country is being able to develop its own vaccines.

“The platform used to produce Abdala´s RBD is the same one that the center used in the past to develop HeberNasVac, a therapeutic vaccine against hepatitis B,” he said.

Another reason Cuba has set out to develop its own vaccines is the international sanctions that are still in place, which make it difficult for the country to acquire products in international markets.

“The embargo and blockade conditions have forced the country to develop its own drugs, especially vaccines. Today, most of those used in the national vaccination program are of domestic manufacture,” said Pérez-Riverol, who said he is confident on the results that Abdala, the vaccine candidate, can achieve, based on the country's past experience with vaccines.

“For more than three decades, Cuba has invested an enormous amount of state economic resources in the development of its biotechnology industry,” he said.

According to records of the Cuban Public Registry of Clinical Trials, the current trial is a multicenter, randomized, double-blind and placebo-controlled one, in which participants, ages 19 to 80, are taking part, to evaluate the efficacy, safety and immunogenicity of the vaccine candidate.

There are 19 sites in the provinces of Santiago de Cuba, Guantanamo and Granma taking part in the trial, which is expected to end by July 31 and to have its results disclosed to the public by mid-August.

International cooperation

As the phase III trials of the Cuban vaccine candidates move forward, the Caribbean country is getting ready to scale up production of its domestic vaccines against SARS-CoV-2. Technology transfer agreements are being discussed both with Iran and Venezuela. A Cuban delegation spent the last few days in the latter inspecting a vaccine manufacturing plant, where the Abdala vaccine is going to be produced, according to the Venezuelan regime.

“We have been accompanied by the Cuban delegation, which has just finished just one week of work in this plant to verify all the conditions that are in place for the production of the vaccine against COVID-19, Abdala", said Delcy Rodriguez, vice president of the Venezuela’s ruling regime, on April 8. The government of Nicolas Maduro is not recognized by several countries, including the U.S.

“This is the way to defeat the pandemic, with solidarity and cooperation; no country can fight and achieve a battle against COVID-19 by itself,” she added.

Pérez-Riverol said Abdala has a series of virtues, including its low-cost ingredients.

“Obtaining it in a relatively inexpensive cellular system such as yeast offers you a productive advantage and can enhance your competitiveness in the market,” he said. “If it proves highly effective in the ongoing phase III trial, it will be a good alternative in dealing with the COVID-19 pandemic.”