Is it because Mr Rao is ill? He is 73 and may require another heart bypass operation, according to the Indian press. Yet he was seen about the capital on Friday, smiling his way through a book launch for a new album of photographs taken by the late Rajiv Gandhi.
Surely the Prime Minister caught sight of all the scooter- drivers with their faces covered with handkerchiefs? Perhaps he even saw the rowdy queues for the antibiotic tetracycline outside chemists.
Mr Rao has yet to visit Surat, the Gujarat city where about 50 people have died from the plague and another 700 are ill; or Maharashtra state, where hundreds more have caught it. Nor has he expressed sympathy for the victims.
His muteness seems to have infected others in the cabinet. Health Minister B Shankaranand waited 72 hours before admitting that pneumonic plague had laid siege to Surat, and sounding the alert. That was long enough for nearly 700,000 terrified people to flee the city by rail, bus and bullock cart, carrying the airborne disease with them.
Among his Congress (I) party critics, Mr Rao has a reputation as a ditherer. But this plague outbreak cannot wait. Had the affected areas of Surat and Maharashtra been sealed off promptly, the outbreak could have been contained. Now, there is a danger of it crossing India's borders.
Faced with government sluggishness, Indians are seeking help from the gods. In Bombay, hundreds of Christians are visiting cemeteries to pray at 'plague crosses', the tombs of ordinary people who survived the Black Death that killed 12.5 million Indians at the turn of the century. And at Hindu temples and shrines, millions are offering money, coconuts and sweets to appease the gods.
One Delhi domestic servant told her employer: 'There is nothing we can do. It's a curse of the gods.' But in her shantytown hut she takes precautions. On her doorstep, she burns a mixture of cow dung and neem leaves. This is not a superstitious concoction, but an ancient Ayurvedic cure. And the city's health minister, a firm believer in Ayurvedic medicines, wants everyone to do likewise.
Plague has frequently visited India. The Hindu Vedic scriptures, which are at least 1,500 years old, linked its onslaught with rats. Even today, at harvest time, many villagers will fill earthen jars with a foul- smelling mass of dung and hay, which they believe will draw the plague away. The jar is secretly buried in the next village.
This sacrifice of one's neighbour is an ugly pattern that surfaces in cities, too. Anyone returning to Delhi from a plague area nowadays can expect his neighbours to have tipped off the police. People have been hoarding tetracycline - an antibiotic that can cure pneumonic plague - so driving up its price.
In Calcutta, some of the city's many Marxists see the plague as the beginning of capitalism's Dark Ages. Meenakshi Dutta, a schoolteacher, said: 'I heard a prominent doctor say the plague was started by multinational companies to sell more drugs to the Third World.'
Although only two victims have died so far in Delhi, and there are only 200 suspected cases among its 9 million people, panic comes in spasms, sometimes on a rumour.
With no expectations of Mr Rao's government, some Delhi- wallahs have been combating the plague their own way: when the city refused to clear a rubbish tip swarming with rats, locals pitched in and carted it away. On the site, they painted pictures of Hindu gods. Even if the deities do not protect them against the plague, at least their images will prevent people from dumping rubbish there.