Shortages of Covid-19 vaccines have forced several large Brazilian cities to suspend administering second doses, officials and media reports said, the latest breakdown in the hard-hit country's troubled immunization drive.

Seven of Brazil's 26 state capitals have stopped administering the booster shot of Chinese-developed CoronaVac because of a lack of supply. More than half Brazil's state capitals do not currently have enough vaccines to ensure everyone who has received a first dose will get the second on time.

Brazil, where Covid-19 has claimed more than 400,000 lives — second only to the United States — is struggling to vaccinate its 212 million people. It has been using two vaccines, both of which require two doses: CoronaVac and the Oxford/AstraZeneca vaccine, AFP reported.