Moderna Inc's experimental vaccine for the novel coronavirus showed it was safe and provoked immune responses in all 45 healthy volunteers in an early-stage study, US researchers have reported.

Moderna's shot, mRNA-1273, uses ribonucleic acid (RNA), a chemical messenger that contains instructions for making proteins.

When injected into people, the vaccine instructs cells to make proteins that mimic the outer surface of the coronavirus, which the body recognises as a foreign invader, and mounts an immune response against.

In June, Moderna said it selected the 100-microgram dose for its late-stage study to minimise adverse reactions.

At that dose, Moderna said the company is on track to deliver about 500 million doses per year, and possibly up to 1 billion doses per year, starting in 2021, from the company's internal US manufacturing site and strategic collaboration with Swiss drugmaker Lonza.

Meanwhile, Tokyo is considering raising its alert for coronavirus infections to the highest of four levels, officials said today, after a spike in cases to record numbers in the Japanese capital.

Fearing a second wave of infections spreading from the capital, municipalities and opposition politicians also urged the central government to suspend a major campaign aimed at boosting domestic tourism, which has also come under fire on social media, with the coronavirus fuelling an unusual outburst of political anger in Japan.

Economy Minister Yasutoshi Nishimura, however, said the government would proceed with the "Go To" travel campaign, which includes offers such as discounts for shopping and food, but it would move cautiously.

In the US, President Donald Trump lambasted California's two largest school districts, in Los Angeles and San Diego, for making students learn from home for the upcoming term in the face of a resurgent coronavirus.

Against the backdrop of rising cases and deaths, US school districts have been confronted with a difficult choice of resuming classes or using only online teaching, which many parents have called ineffective and burdensome.

Mr Trump has said he may withhold federal funds or remove tax-exempt status from schools that do not open. It is not clear how funds could be withheld. Most primary and secondary school funding is local.

The country's 98,000 public schools are a cornerstone of the economy, providing childcare for working parents, employing eight million people, prior to the pandemic, and preparing some 50 million students to join the US workforce.

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Disneyland Paris welcomed back visitors today after a four-month closure due to the coronavirus outbreak, with face masks and social distancing the order of the day.

A steady stream of visitors trickled in during the morning, with one group wearing Mickey Mouse ears and dancing with gleeas they entered Europe's most visited theme park.

Masks were mandatory and advance booking required. Visitors to the park, which has imposed a limited capacity, were told to keep a metre away from others, and hundreds of sanitising gel and hand-washing stations were scattered around.

No tickets were sold at the entrance and rides where social distancing is difficult have not yet reopened.

Playgrounds and make-up workshops also remained closed.

Walt Disney World also reopened its two most popular parks in Orlando, on Saturday, despite a surge of new infections in Florida.

But in Hong Kong, the company has decided to temporarily close its Disneyland park amid rising coronavirus cases in the Chinese-ruled city.

The World Health Organization has said the number of confirmed coronavirus cases globally has surpassed 12.96 million.