Europe's drug regulator was expected to rule Tuesday on the safety of the Johnson & Johnson Covid-19 vaccine after fears it could be linked to extremely rare blood clots, while India said it will make shots available to all adults as it battles a terrifying wave of infections.

The United States is also expected to announce its decision on the single-shot J&J vaccine by Friday, as nations around the world try to accelerate their rollouts and revive their pandemic-ravaged economies.

The European Medicines Agency was due to hold a press conference from Amsterdam on Tuesday, after reviewing four cases -- one fatal -- of rare blood clots reported among people who got the J&J shot.

But the number of reported clots were "extremely small" compared with the 4.5 million J&J shots administered worldwide, the EMA has said.

That comparison echoes the comments by top US pandemic advisor Anthony Fauci, who described the clots as "an extraordinarily rare event".

Fauci said Sunday he believed the US would resume use of the jab, possibly with some restrictions or warnings.

The J&J vaccine concerns follow similar reports of blood clots in a very small number of people who received the AstraZeneca shot.

The EMA described those clots as a "very rare" side effect, stressing that the AstraZeneca jab's benefits outweigh the risks.

The leaders of Europe are keen to accelerate vaccinations and expand availability after facing intense criticism over a sluggish rollout and with the public desperate for a return to some degree of normality.

That desire was on display in EU member Slovakia on Monday, where shops, museums, libraries and swimming pools reopened after a lengthy lockdown, bringing big crowds onto the streets.

Hairdressers were in particularly high demand.

"We have been very busy since the morning, but I am very happy that we can cut hair again," said Martin, a Bratislava barber.

- Crisis in India -
India, home to 1.3 billion people, is battling a worrying surge, with record daily case numbers overwhelming already stretched hospitals and medical supplies.

Its capital New Delhi was locked down Monday for a week, and the government said all adults would be eligible for a vaccine from May as it tries to get a grip on the spike.

Similar measures have been taken in other Indian states, adding to the woes of people already reeling from the economic pressure of the pandemic.

The looming lockdown in Delhi forced tens of thousands of migrant workers to try and flee on Monday, fuelling fears they could spread the virus to their rural hometowns.

"Last year I was stuck here for 50 days," said tailor Hari Shankar, referring to the strict coronavirus lockdown India imposed last year.

"I didn't have work and couldn't send money home... I'm not planning on coming back (to Delhi) until Covid is over."

Experts have warned that religious festivals, including the Kumbh Mela attended by millions of pilgrims, and packed state election rallies in India had become "super-spreader" events -- and some have said mass vaccinations are the only long-term solution.

- Vaccine inequality -
There are concerns, however, that vaccine inequality between wealthy and poor nations will further complicate and prolong the pandemic.

Climate activist Greta Thunberg became the latest high-profile figure to criticise the lopsided distribution, describing vaccine inequity as a "tragedy".

The 18-year-old donated 100,000 euros ($120,000) from her foundation to the Covax scheme, which is helping with global access to vaccines -- especially in poorer countries.

Mass vaccinations are considered key for resuming regular life and economic activity, especially travel.

But the World Health Organization's emergency committee said it was against international passengers being required to have proof of vaccination -- a proposal being mulled by numerous countries.

The committee said such requirements would "deepen inequities and promote differential freedom of movement" because of the uneven global vaccine rollout.

But the threat of the virus being spread by international travellers was brought into sharp focus in Hong Kong, where at least 49 passengers on a single flight from India tested positive.