NEW DELHI (AP) — India started inoculating health workers Saturday in what is likely the world's largest COVID-19 vaccination campaign, joining the ranks of wealthier nations where the effort is already well underway.

The country is home to the world's largest vaccine makers and has one of the biggest immunization programs. But there is no playbook for the enormity of the challenge.

Indian authorities hope to give shots to 300 million people, roughly the population of the U.S and several times more than its existing program that targets 26 million infants. The recipients include 30 million doctors, nurses and other front-line workers to be followed by 270 million others, who are either aged over 50 or have illnesses that make them vulnerable to COVID-19.

Health officials haven't specified what percentage of the nearly 1.4 billion people will be targeted by the campaign. But experts say it will almost certainly be the largest such drive globally.

The sheer scale has its obstacles. For instance, India plans to rely heavily on a digital platform to track the shipment and delivery of vaccines. But public health experts point out that the internet remains patchy in large parts of the country, and some remote villages are entirely unconnected.