PARIS－Europe's stuttering vaccine drive faced multiple hurdles as EU regulators said on Friday they were reviewing side effects of the Johnson & Johnson vaccine.

As the continent continues to reel from constant rows over AstraZeneca's vaccine, whose use has been limited in some countries because of blood clots, the EU's medicine regulator announced it would be investigating a second vaccine over similar concerns.

The European Medicines Agency said four "serious cases" of unusual blood clots had been reported, one fatal, with the J&J vaccine, which uses technology similar to that used in the AstraZeneca one.

The US drugs regulator said it had not found a causal link between the J&J vaccine and blood clots, but that its investigation was continuing after "a few individuals" suffered complications.

The company issued a statement saying: "At present, no clear causal relationship has been established between these rare events and the Janssen COVID-19 vaccine," referring to J&J's European subsidiary.

Both vaccines are approved for use in the European Union but the J&J vaccine has yet to be introduced, and various EU countries have stopped or limited the use of the AstraZeneca vaccine.

Much of the world is still in the clutches of the pandemic, which has killed 2.9 million people, and across Europe populations are facing some of the world's toughest antivirus measures, yet the virus refuses to be curbed.

Italy recorded 718 deaths on Friday, its highest number in months, but health officials said the spike from 487 a day earlier was due to a backlog of deaths being reported in Sicily.

The country's death toll has remained stubbornly high as the vaccination campaign for the most vulnerable population has lagged.

The President of Italy's National Health Institute, Silvio Brusaferro, said the new contagion that was first detected in the United Kingdom has reached a plateau in Italy, with 18,938 new cases on Friday. Much of the country remains on partial lockdown.

Germany's central government has tried hard to defeat the virus through restrictions on movement and commerce, but several states have torpedoed the strategy by refusing to go along with the proposals.

Now Berlin is changing the rules to gather more centralized power.

The proposed adjustments are likely to usher in curfews and some school closures in especially hard-hit areas.

The number of confirmed cases in Germany rose by 17,855 to 2,998,268, according to figures on Sunday from the Robert Koch Institute for infectious diseases.

All of France is subjected to restrictions of some form, and more than 10 million people in the country have received the vaccine.

Doubts on efficacy

But the country has repeatedly changed the rules on AstraZeneca's vaccine, first over doubts about its efficacy, then over fears that it could be linked to blood clots.

On Friday it did so again, with Health Minister Olivier Veran saying citizens under 55 who had been given a first shot with AstraZeneca would be given a different vaccine for their second dose.

Elsewhere in the world, supply problems are also hampering vaccination efforts.

India, one of the world's leading vaccine makers, is suffering its own problems with vaccination in Maharashtra, home to more than 100 million people, and the economic hub Mumbai.

"Most hospitals in Mumbai will exhaust their supplies by the end of the day," Mangala Gomare, who oversees the city's vaccination program, said on Friday.

Agencies via Xinhua