"When you're dealing with vaccines there could be so many things that get in the way like it might not be entirely effective", he said.
Bharat Biotech, a country-based private firm, is aggressively working to develop and test a vaccine for Covid-19 and, in this regard, the company has formed a wider collaboration with many institutions, including the country's government-owned Indian Council for Medical Research (ICMR).
Earlier this week, drugmaker AstraZeneca said it had secured its first agreements for 400 million doses of the Oxford-developed vaccine, bolstered by a $1 billion investment from a US government agency, for the development, production and delivery of the vaccine, starting in the fall.
Fourteen percent of respondents said they were not at all interested in taking a vaccine, and 10 percent said they were not very interested.
In the USA, the Trump administration has launched Operation Warp Speed, a public-private partnership that includes the Departments of Health and Human Services, Defense, Agriculture, Energy and Veterans Affairs to work on treatments and vaccines against the virus.
"If all the cards fall into the right place and all the stars are aligned, you definitely could get a vaccine by December or January", Dr Fauci said.
About a dozen different experimental vaccines are in early stages of human testing or poised to start, mostly in China, the USA and Europe, with dozens more in earlier stages of development.
"I would have expected somewhere around 75%".
Following this, the team regularly tested the volunteers" blood to assess if the vaccine activated the two parts of the body's immune system: The "humoral response' and the T-cell response.
Professor Kim Woo-ju of the Infectious Disease Department of Korea University Guro Hospital made the warning on a YouTube live program on Thursday to analyze the interim results of Moderna's phase-1 study on mRNA-1273, a potential Covid-19 vaccine.
In previous interviews, Fauci says the first COVID-19 vaccine could be available in early 2021 if all goes well.
On Thursday, the U.S. government agreed to pay the British pharmaceutical giant AstraZeneca up to $1.2 billion to secure 300 million doses of its experimental vaccine.
Another 26% said they were unsure about getting innoculated, while one in five said that they not get vaccinated at all.
He has at times downplayed the seriousness of the pandemic and encouraged public protests against his government's own stay-at-home guidelines meant to slow the pathogen's spread.
The poll responses varied among certain demographic groups.
Any vaccine will be met by massive global demand requiring billions of doses and a total shift in approach to how vaccines are typically developed. More than 40 percent said Trump's reassurance would make them less willing to take it.
The survey was conducted between May 4 and 5 and used a sample of 1,574 adults.