China's vaccine only 50.4% effective, Brazilian trial shows

A Brazilian clinical trial has shown that developed by China's Sinovac has been found to be 50.4% effective.

The Chinese, which is one of the two lined up by the Brazilian government, is significantly less effective than previous data showed - barely over the 50% needed for regulatory approval.

Sinovac, a Beijing-based biopharmaceutical company, is behind CoronaVac, an inactivated vaccine. It works by using killed viral particles to expose the body's immune system to the virus without risking a serious disease response.

Apart from Brazil which is the second most hit nation in the world, several other countries like Singapore and Turkey are also awaiting the vaccine.

However, researchers at the Butantan Institute in Brazil, last week announced that the vaccine had a 78% efficacy against "mild-to-severe" Covid-19 cases.

They on Tuesday disclosed that the data that the calculations for this figure did not include data from a group of "very mild infections" among those who received the vaccine that did not require clinical assistance. 

This mean including these data brings the efficacy rate to 50.4%, said researchers.

Butantan noted that the vaccine is 78% effective in preventing mild cases that needed treatment and 100% effective in staving off moderate to serious cases. 

The new data in Brazil means varying results are are got in different countries. Last month Turkish researchers said the Sinovac vaccine was 91.25% effective, while Indonesia, which rolled out its mass vaccination programme on Wednesday, said it was 65.3% effective. Both were interim results from late-stage trials.

This doesn't mean result are universal, as research have shown how difficult it is to compare vaccines worldwide.

On the face of it, the 50% effectiveness figure isn't as good as Oxford's 70% or Pfizer and Moderna's 95%. But trials are run very differently in different countries - the numbers of volunteers enrolled varies wildly, genes of people of different areas and the criteria used to test how much protection the vaccines offer.

Each country may need to test the vaccine within its territory to ascertain the result of vaccine which will perfectly work for its people.

So it is only when the full data from all trials of this vaccine are published that scientists can analyse its real efficacy, and compare like with like. Only limited data for this Sinovac vaccine is currently available - and experts say that is confusing the picture. 

Also, Chinese vaccine may not be really banked on, as critics believe that Chinese vaccine trials are not subject to the same scrutiny and levels of transparency as other western countries.