Adar Poonawalla, Chief Executive of Serum Institute of India (SII), on Monday said it was not possible to ramp up vaccine production overnight as it a very "specialised process".

In a statement on Twitter, Poonawalla said, "Vaccine manufacturing is a specialized process. Therefore it is not possible to ramp up production overnight. We also need to understand that the population of India is huge and to produce enough doses for all adults is not an easy task."

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"Even the most advanced countries and companies are struggling in relatively smaller populations." 

His statement came as a clarifiaction over his earlier comments regarding facing pressure over the supply of the Covishield vaccine, manufacturered by his Pune-based firm. 

In an interview with the Times newspaper on Saturday, the 40-year-old alleged he was getting aggressive calls from the 'most powerful', including chief ministers, business tycoons and others, over the supply of the vaccine. 

He further stated he was given Y-category security after receiving a number of threats over the supply of vaccines. It was one of the reasons behind his decision to move to London temporarily, he said.  

Meanwhile, in his statement, Poonawalla said that his firm has received total orders of over 26 crore doses from the Centre, of which 15 crore doses have been supplied. 

"We have been working closely with Government of India since April last year. We have got all kinds of support, be it scientific, regulatory and financial."

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He further stated that his firm has received a 100% advance payment of Rs 1,732.50 crore for the next tranche of 11 crore doses, which will be supplied over the next few months. A further 11 crore doses will be supplied to states and private hospitals. 

SII had initially agreed to sell its Covishield vaccine to the Centre for Rs 150 per dose. It recently cut down its price to state governments from Rs 400 to Rs 300 per dose. For private hospitals, it has priced the shots at Rs 600 per dose. 

"We understand that everyone wants the vaccine to be available in the quickest possible time. That is our endeavour too and we are making every effort to acheive that. We shall work even harder and strenghten India's fight against Covid-19," he added.