The vaccines, which are administered in two doses spaced 21 or 28 days apart, are especially safe because they do not contain the live virus that causes COVID-19.
Simultaneous inauguration ceremonies, held in major cities of all provinces as well as in Azad Jammu and Kashmir and Gilgit Baltistan, were attended by the respective chief executives and other high-ranking officials.
The total number of doses provided up to Wednesday stands at 3,691,591 with a rate of vaccine distribution of 37.32 doses per 100 people.
The vaccine from Pfizer and BioNTech, based on similar technology, has been put into the arms of thousands of US healthcare workers this week in a massive nationwide rollout. Moderna injections are expected to begin in coming days for adults 18 years
In a recent survey, people who said social distancing and COVID-safety guidelines violated their personal freedoms responded more positively to these ideas when they felt a loved one might be at risk of severe illness.
Amid record coronavirus infections and deaths, Moderna has already moved vaccine supplies from its manufacturing plants to warehouses operated by distributor McKesson Corp.
"Since vaccination requirements vary by country and some require second doses, it is important to visit a travel clinic at least one month prior to travel," said Dr Alia Mohammad Al Dallal.
"In the Pfizer contract it's very clear: 'we're not responsible for any side effects.' If you turn into a crocodile, it's your problem," Bolsonaro said.
Oman, with more than 128,000 recorded cases, 1,491 of them fatal, is to launch its vaccination campaign on Sunday.
Frontline medical staff in Mexico and Chile were among the first to receive their vaccines while Costa Rica began its own immunisation programme, with President Carlos Alvarado hailing what “may be the beginning of the end of this pandemic.”