Covaxin 50% Effective, Finds Real World Lancet Study: What Does It Mean?

Bharat Biotech's COVID-19 Vaccine, Covaxin is 50 percent effective against symptomatic illness, finds a real world study published in the Lancet Infectious Diseases Journal.

The study was conducted during the peak of the second wave in India, and assessed vaccinated healthcare workers from All India Institute of Medical Sciences (AIIMS).

This was also the time when the Delta variant was the dominant strain of COVID in the country, which makes a case for Covaxin's effectiveness against the variant, according to the study authors.

As a point of comparison, interim trial results showed Covaxin to have an efficacy of 77.8 percent against symptomatic illness, in a clinical setting.

"Our study offers a more complete picture of how BBV152 (Covaxin) performs in the field and should be considered in the context of COVID-19 surge conditions in India, combined with the possible immune evasive potential of the Delta variant."

Manish Soneja, Additional Professor of Medicine at AIIMS New Delhi, as quotesd by PTI

Let's break down the findings of the study. What does this 50 percent effectiveness really mean?

Key Points of the Study

• The study was conducted to gauge the real world effectiveness of the Covaxin COVID-19 vaccine in preventing symptomatic illness.

• It was conducted between 15 April to 15 May –in the thick of the second COVID wave in India.

• It involved 1068 pairs of employees at AIIMS who were at a higher risk of exposure and infection.

• Half the participants had symptomatic COVID confirmed by RT-PCR tests.

• These test subjects were then matched with the other half (control cases) on a 1:1 ratio based on gender and age.

The study found Covaxin to be 50 percent effective in preventing symptomatic COVID-19 after 2 doses with a gap of 14 days.

In patients who had received the vaccine 28 days before testing, the effectiveness was found to be 46 percent.

The adjusted effectiveness of the vaccine who received it at least 42 days before testing was 57 percent.

Key Takeaways & Limitations of the Study

Real world studies such as this one are important to gauge the true performance of the vaccines in the masses, as these are likely to vary from the clinical trial data.

One reason why this study threw up data so much lower than Covaxin's clinical trial results could be that it was conducted at the peak of the second wave, when testing and test positivity rates were particularly high.

Furthermore, since delta is also known to be able to circumvent vaccine protection, it could explain the lower efficacy noted in the study.

Another reason could be that it was conducted on healthcare workers who are, as it is, at a higher risk of infection due to higher exposure.

But 50 percent efficacy against symptomatic illness is not bad news, say experts.

In fact, it's encouraging news considering the second wave was largely dominated by the delta variant, known to be far more virulent than the original strain.

However, it must also be noted that participants in the study were not tested for specific variants, so it can't be said for certain how effective Covaxin is against the delta variant.

How Does it Compare to Covishield?

How does, then, this performance by Covaxin compare to Covishield, the other widely administered COVID-19 vaccine in India?

The simple answer is not the most satisfactory—at this point, we can't say.

It's difficult to make a direct comparison of this data with Covishield's performance as study designs have differed.

However, another large scale real-world study conducted by the ICMR (Indian Council of Medical Research) and made public earlier his week, compared the effectiveness of Covaxin and Covishield in preventing severe disease.

The study—yet to be peer reviewed— found that, while Covishield elicited 80 percent efficacy against severe COVID, Covaxin was found to be 69 percent effective.

Another point of difference between the two studies is that while this one was conducted on COVID positive symptomatic and COVID negative healthcare workers, the previous ICMR study compared severely ill and hospitalised COVID patients to COVID negative people.

The results of the ICMR study shows a higher effectiveness (in case of both vaccines) as the main job of the COVID vaccines is to prevent severe illness, according to experts.

In a clinical trial setting, Covishield was found to be 66.7 percent efficacious in preventing symptomatic illness at least 14 days after the second dose.

(Written with inputs from PTI and the Indian Express.)