Updated: March 4, 2021 10:01:15 am
What does the ‘efficacy’ of a vaccine mean?
Efficacy is a measure of how much the shot protects people against a virus or bacteria, compared with the situation in which they were not vaccinated. Efficacy looks at the ability of the vaccine to protect the inoculated population using various parameters — ranging from the ability of the shot to prevent mild to severe symptoms from showing even if you have been infected, to preventing you from getting infected with the disease altogether.
In the case of Covid-19 vaccines, pharma companies have primarily focussed on bringing down the number of symptomatic cases — even if you’re infected with SARS-CoV-2, you may not present with the symptoms and fall as sick as you would have without the vaccine.
Bharat Biotech, through its phase 3 clinical trials involving 25,800 volunteers across the country, has also focussed on understanding Covaxin’s efficacy in preventing symptomatic, including severely symptomatic, Covid-19 cases.
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What do the Covaxin interim data say?
According to the interim results, the vaccine has an efficacy of 80.6 per cent. This means the vaccine was able to bring down the number of symptomatic Covid-19 cases by nearly 81 per cent in those vaccinated in the trial as compared to the group that received a placebo.
The results were collected by studying 43 participants in the trial who had tested positive for Covid-19 two weeks after receiving their second dose, and had presented with mild, moderate, or severe symptoms. The trials were unblinded at this point to check how many of these participants had received Covaxin and how many had got a placebo.
It was found that 36 out of these 43 participants had received a placebo, while seven had received Covaxin.
These results have so far not been published in a scientific journal or have been peer-reviewed.
Why are the results announced on Wednesday important?
Covaxin is one of the two vaccines being used in India’s mass vaccination programme against Covid-19. A higher efficacy would mean a higher chance at protecting the vulnerable population against the disease.
The findings are expected to add value to the vaccine and ease hesitancy related to it. The vaccine had earlier come under fire for having received emergency approval without Bharat Biotech recruiting and vaccinating enough participants in its phase 3 trial to even provide an idea of its efficacy. This meant, until now, no one knew how much protection this vaccine would actually be able to provide to those receiving it.
“It’s a bit of a relief,” said vaccine expert Dr Gagandeep Kang, vice chair of CEPI and professor at Christian Medical College-Vellore. “The interim analyses actually test the vaccine much more, so if it has around 81 per cent efficacy, then that means it is likely to maintain a high level of efficacy even when the full results are released,” she said.
How does Covaxin stack up against other Covid-19 vaccines?
* Covishield, the other vaccine being used in the government’s campaign, has an efficacy of around 53 per cent when the second dose is given less than six weeks after the first dose, according to its product insert.
However, the efficacy of this vaccine, which is based on the AstraZeneca-University of Oxford jab AZD1222, varies based on the duration between the first and second shots. According to Covishield’s product insert, this efficacy changes to nearly 79 per cent if the second dose is administered at 12 weeks or longer. At the same time, as per the regulatory approval to Covishield as of now, the second dose has to be given 4-6 weeks after the first dose.
* Serum Institute of India, which manufactures Covishield, will also be making Covovax — a version of the Covid-19 vaccine developed by Maryland, US-based Novavax Inc. In January, this vaccine demonstrated an efficacy of around 89.3 per cent in the UK, and around 60 per cent in South Africa.
* Pfizer and BioNTech’s BNT162b2, which is currently not available in India, has demonstrated an efficacy of around 95 per cent. The vaccine developed by Moderna and the US National Institute of Allergy and Infectious Diseases (NIAID) has shown an efficacy of around 94 per cent.
* Last month, Sputnik V, the Covid-19 vaccine developed by Moscow’s Gamaleya Research Institute of Epidemiology and Microbiology, was found to have an efficacy of 91.6 per cent. This vaccine has been tested in phase 2/3 clinical trials in India by Dr Reddy’s Laboratories on around 1,500 volunteers.
The Hyderabad-based pharmaceutical company approached the Indian drug regulator on February 19 seeking restricted emergency use approval for Sputnik V. It submitted interim data demonstrating the vaccine’s safety and ability to produce an immune response, as well as efficacy data from its trials in Russia.
* Johnson & Johnson, which has been working on a single-dose Covid-19 vaccine, said on January 29 that its shot had an interim efficacy of 72 per cent in the US, 66 per cent in Latin America, and 57 per cent in South Africa. Across all its trials, the vaccine demonstrated an efficacy of around 66 per cent.
Should we be comparing the efficacy of vaccines?
There is disagreement over this point. But most experts feel it may not be fair to compare vaccines using different platforms and different clinical trial designs.
In the case of Covaxin, the data released is based on only 43 cases of Covid-19; Bharat Biotech expects to get a clearer picture of its efficacy once 130 cases are accumulated among its participants.
“This is good, but it’s not complete (data), unlike the AstraZeneca vaccine, where the full phase 3 study is over and they met their total case numbers. Their full analysis was in December, so they’re kind of done with the study, while Bharat Biotech still has a way to go,” Dr Kang said.
But even if the data were final, a comparison would not be appropriate, Dr Kang said. “No two trials are identical,” she said.
However, some experts feel that if there is a very large difference in the efficacy values being reported for these vaccines, it could make a difference in how effectively a country is able to tackle the pandemic.
“Given that we are in a pandemic, and that we now have multiple vaccines, I think comparing an 80 per cent efficacious vaccine versus a 90 per cent one is perhaps not reasonable,” said Massachusetts-based vaccine expert Dr Davinder Gill. “But it’s definitely fair to compare a 60 per cent efficacious vaccine with one that is 90 per cent efficacious. That’s a pretty big difference.”
So what do we not know yet about Covaxin?
There is still a lot left to know about Covaxin’s safety and aspects related to its efficacy, according to experts.
“These are topline numbers… Bharat Biotech, interestingly, in their protocol is also looking at preventing asymptomatic cases as a secondary outcome,” Dr Kang said. “So, this will be a vaccine that is also going to give us information on potential protection against infection and potentially for reduction in transmission,” she said.
“All the details related to whether they’re looking at mild, moderate, and severe disease, the split between different age groups, genders, and co-morbidities, and the entire safety profile — serious adverse reactions…all those details are missing at the moment. I think the complete picture cannot really be obtained until these additional interim points are clearer,” Dr Gill said.
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