EXPLAINED | Covaxin shows 81% efficacy, here's how it stacks up against Covishield

Covaxin is based on an inactivated whole SARS-CoV-2 virion, an old platform that is also used to make polio vaccines. A virus’s disease-producing capacity is inactivated under this method.

Covishield is based on the viral vector platform. A chimpanzee adenovirus called ChAdOx1 is the vector that has been modified to carry the coronavirus spike protein into human cells. The adenovirus vector platform for vaccines gained traction during the battle to stop Ebola.

Safety and Immunogenicity

Both the vaccines have been found to be safe and have produced immunogenicity in animal and human studies.

Efficacy 

Covishield has an efficacy of 70.4 percent on an average in preventing COVID-19, as per the interim analysis of its late-stage clinical trials conducted in the UK and Brazil.

In Brazil, two full doses of the vaccine were given one month apart, involving 8,895 participants, and the vaccine appeared to be 62 percent effective.

SII conducted a bridge study in India on 1,600 volunteers using the same dosing regimen as Brazil. The bridge study is not meant to measure efficacy; it's used to find out safety and immunogenicity in the local population.

Bharat Biotech conducted its clinical trial in India involving 25,800 subjects in Phase-3, the largest ever conducted in India.

Covaxin demonstrated 81 percent interim efficacy in preventing COVID-19 in those without prior infection after the second dose, the company said in a statement.

“Data from 25,800 participants received a vaccine or placebo in a 1:1 ratio showed that the vaccine candidate was well tolerated,” the company said in the statement.

The first interim analysis is based on 43 cases, of which 36 cases of COVID-19 were observed in the placebo group versus 7 cases observed in the Covaxin group, resulting in a point estimate of vaccine efficacy of 80.6 percent.

Bharat Biotech said it would share second interim analysis data based on 87 cases, and the final analysis is planned for 130 cases in coming weeks. To be sure, data from those analysis will give more accurate picture on the efficacy of the vaccine.

On new variants

Both the vaccines have been found to be effective against the UK variant of coronavirus. While AstraZeneca-Oxford vaccine is found to have only 10 percent efficacy against South African variant N501Y, Covaxin is yet to be tested on this strain.

So far data suggests that COVID-19 vaccines may not fully protect from infection, but prevent severe COVID-19 that's linked to hospitalisation and death.

In theory, the inactivated vaccines, such as Covaxin, provide broader protection against mutating variants.

AstraZeneca said it is updating its COVID-19 vaccine to make it effective against new variants.

Logistics and supply chain

Both the vaccines are stable at 2 to 8°C (refrigerator temperature) and are shipped in a ready-to-use liquid formulation that permits distribution using existing vaccine supply chain.

Where is it approved?

AstraZeneca jab is widely used globally. The vaccine is approved by the WHO and dozens of other countries, including India for emergency use. More than 300 million doses of the vaccine will be made available to 145 countries through the WHO's COVAX. These will be largely supplied by SII.

Bharat Biotech's jab is approved for restricted emergency use in clinical trial mode. Brazil has signed up for 40 million doses. The vaccine maker has said more than 40 countries globally have expressed their interest in Covaxin.