As the rest of the world struggles to vaccinate adults in the face of a threat from a new coronavirus variant, China has embarked on an ambitious campaign that it says will give the country better protection against Covid-19: full inoculation of 160 million of its youngest citizens by the end of the year.

       The campaign — powered in part with red flower stickers, balloons and boxes of toys for children who step up to become what nurses call “little inoculated warriors” — has gotten off to a fast start. In the first two weeks of the effort, which began in late October, 84 million boys and girls between the ages of 3 and 11, about half of the eligible population, received the first of two shots, according to the most recent government data.

       By contrast, in the United States, 2.6 million children between ages 5 and 11, or about 10 percent of the eligible population, received one dose over roughly the same time period.

       The push is part of Beijing’s unrelenting march toward herd immunity, the point at which enough people are immune to the virus that it cannot spread through the population. With less than three months before the Winter Olympics in Beijing, Chinese officials are doubling down on that strategy. And with 1.1 billion adults already vaccinated, young people are seen as an important part of its success.

       The campaign faces significant obstacles, including parental reluctance in a country with a checkered history of safety on children’s vaccines. The government insists that child inoculations are voluntary, but parents have described coming under pressure to get their children vaccinated.