“There are no mechanisms for compulsory [vaccination]. I mean we can’t hold someone down and make them take it…that doesn’t happen anywhere in Australia today under any of those systems, and that’s not what people are proposing,” Morrison said on Australian radio station 2GB on Wednesday evening.

Morrison had suggested earlier on Wednesday on 3AW, another Australian radio station, that a coronavirus vaccine might be mandatory, saying that medical grounds “should be the only basis” for vaccination exemptions.

Karen Andrews, Australia’s minister for science and industry, echoed Morrison’s remarks on Wednesday, saying on 2GB, “The Prime Minister’s made it clear that we are looking at it being a mandatory vaccine.”

But hours later, after online backlash from anti-vaccination groups in Australia and elsewhere, Morrison backtracked on his earlier remarks, telling 2GB the vaccine would not be compulsory. Morrison also said there was “a bit of an overreaction” to his remark about a mandatory vaccine.

The swift public reaction to Morrison’s comments underscores the politically fraught nature of population-wide vaccination campaigns, and the delicacy with which governments will need to handle the issue if and when a COVID-19 vaccine is ready.

Vaccines are some of the safest medicines in existence; distribution of a coronavirus vaccine, once one proves safe and effective, will be key to saving lives and ending the pandemic.

Australia on Tuesday reached an agreement with British pharmaceutical giant AstraZeneca to produce and distribute 25 million doses of the AstraZeneca- and Oxford University–developed coronavirus vaccine candidate, AZD1222, for the Australian population.

AZD1222, widely considered the global frontrunner for a coronavirus vaccine, is currently undergoing human clinical trials. Morrison said he hopes to make the vaccine doses free and available to all Australians in early 2021 if the trials are successful.

Hundreds of anti-vaccination protesters rallied across cities in Australia in May, calling the pandemic a “scam,” breaching social distancing regulations, singing anti-vaccination songs, and holding up placards that opposed “mandatory” vaccines.

Morrison has long been associated with vaccination efforts. When he served as Australia’s minister for social services in 2014 and 2015, Australia passed national and state legislation called “No jab, no play” that required children to receive certain immunizations in order for their families to be eligible for childcare fee assistance and other benefits.

The immunization requirement originally exempted people with medical reasons, people who submitted a conscientious objection to immunization, and members of the Church of Christ, Scientist. In April 2015, Morrison announced that the Christian Scientist and conscientious objector exemptions would be removed.

Morrison pointed out that he had established “No jab, no play” while speaking to 3AW earlier on Wednesday, raising speculation that the government might introduce similar measures to encourage uptake of the coronavirus vaccine.

“There will be no compulsory vaccine, but there will be a lot of encouragement and measures to get as high a rate of acceptance as usual,” Morrison told 2GB.

The Prime Minister did not specify what the measures might entail. He said he hoped Australia would achieve at least a 95% vaccination rate for the coronavirus, and he cited the country’s high immunization rates for other diseases as evidence that it would be able to achieve a similar rate for coronavirus vaccination.

In the U.S., by comparison, 35% of Americans say they won’t take a coronavirus vaccine, according to an NPR–PBS NewsHour–Marist poll released last week. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said on Tuesday he does not see the U.S. government making a coronavirus vaccine compulsory.