Cuba’s COVID vaccines: The limited data available suggests they’re highly effective

PTI, Dec 8, 2021, 9:48 AM IST

Southampton: The western world has written plenty about its high-profile COVID vaccines: the mRNA products of Pfizer and Moderna, viral-vectored jabs from AstraZeneca and Johnson & Johnson, and those that are just emerging, such as Novavax’s protein-based vaccine. Many countries are relying on them for protection.

But not Cuba. It’s been quietly working on its own vaccines, immunising its population and selling doses abroad.

Cuba’s vaccine efforts have maintained a relatively low profile in the west to date. Politics may well be a reason. The US embargo against Cuba that began in the cold war is still in effect, and tensions between the countries remain high.

But for those familiar with Cuba, its COVID vaccine development should come as no surprise – the country has a long history of manufacturing its own vaccines and medicines. Nor should it be surprising that two of its COVID vaccines – Abdala and Soberana 02 – appear to have performed very well in trials. Here’s how they work.

Abdala is a protein subunit vaccine, which is a well-established design. The hepatitis B vaccine and Novavax COVID vaccine use this approach. These vaccines work by delivering just a portion of the virus that they’re targeted against – in the case of Abdala, bits of the coronavirus’s spike proteins, which cover its exterior.

The proteins used in the vaccine aren’t taken from the coronavirus directly. Instead, they’re grown in cells of a yeast (Pichia pastoris) that have been specially engineered.

On their own, the portions of spike protein are harmless. But when the immune system encounters them, it still trains itself to recognize and destroy them. If the full coronavirus is then encountered in the future, the body will attack these outer parts of the virus and quickly destroy it. Abdala is given in three doses.

The other Cuban COVID vaccine, Soberana 02, uses a “conjugate” design, along the lines of meningitis or typhoid vaccines. It contains a different part of the spike protein to Abdala and generates an immune response by attaching (conjugating) this to a harmless extract from the tetanus toxin. When the body encounters these linked together, it launches a stronger immune response than it would to either alone.

Soberana 02 is produced in hamster ovary cells, a process that can be slow, and this may restrict large-scale manufacturing.

Originally, it was given as two doses, but researchers later identified that a third dose would be beneficial. This booster dose contains just the spike protein parts, without the tetanus toxin, and is known as “Soberana Plus”.

How effective are they? Both vaccines have been approved by the Cuban regulator, though they started being rolled out in May – before authorisation had been granted – in response to a rise in cases. There have been concerns about a lack of information on their safety and efficacy.

On November 1, 2021, a pre-print (research still awaiting review) was finally published of a Soberana phase 3 trial that included 44,031 participants. The results suggest that two doses of Soberana 02 with a booster of Soberana Plus are together 92% protective against symptomatic COVID.

The pre-print notes that during the trial, the vaccine was most likely being tested against beta or delta – two variants of the coronavirus that other vaccines have found harder to control.

Before this, a phase 1 study of giving Soberana Plus to people who had already had COVID was published in September. This was testing the effects of Soberana Plus as a booster to natural rather than vaccine-induced immunity. It showed no safety issues and stimulated a good immune response when used in this way – though the study was small, involving just 30 participants.

For Abdala, the only phase 3 trial data available was issued by Cuban press releases in June and July 2021. The three-dose schedule is also reportedly 92% protective against symptomatic COVID as well as allegedly fully protective against severe disease and death.

This generated huge enthusiasm within Cuba. However, since then little further information has been made publicly available.

Around 90% of Cuba’s 11 million people have received at least one dose of a COVID vaccine, with 82% considered fully vaccinated, and it appears Cuba is vaccinating children as young as two. Both Abdala and Soberana have been used, with around 8 million people receiving three doses of Abdala.

Following a big spike in cases in August 2021 – when the country’s vaccine coverage was still relatively low – new infections in Cuba have since declined greatly and remain low. Without proper studies, it’s difficult to gauge how much of this is down to the vaccines, but the virus’s suppression coinciding with the country reaching high vaccine coverage is a positive sign.

Who could use a Cuban vaccine? Given the difficult relationship between Cuba and the US, the market for Cuba’s vaccines will probably be its political allies. Vietnam and Venezuela are reported to have received Abdala doses, Nicaragua has given emergency authorization to both vaccines, and doses have previously been sent to Iran for use in clinical trials. Mexico and Argentina are also interested in using these vaccines.

Cuba has submitted both to the World Health Organisation (WHO) for approval, which would improve the likelihood of them being used abroad. If there are any plans to include them in the Covax vaccine-sharing initiative, then WHO approval is a must.

Meanwhile, we’re still waiting to see what impact omicron will have. So long as there’s unequal access to vaccines, the pandemic will continue – and so too the risk of new variants arising.

Given most richer countries aren’t in the queue for Abdala or Soberana 02, it’s entirely possible that in future, parts of South America, Asia and Africa – where vaccine coverage is particularly low – may see Cuban vaccines in many arms.

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