India, July 13 -- The US drug regulator has warned of an "increased risk" of an immunological disorder among those administered Johnson & Johnson's single-dose Covid-19 vaccine, known as Janssen, which has had an episodic roll-out in America marked by major manufacturing glitches and suspended use.

Separately, top US health officials also said they would like to see more data before agreeing to Pfizer's recent assertion that a booster dose of their vaccine might be needed. They had an hour-long meeting with the company's experts, who cited an Israeli study in support of their recommendation. Israel began administering a booster - third dose - of the Pfizer vaccine to heart-transplant patients and those with compromised immune systems.

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