NEW YORK • Now it is Moderna's time to be in the spotlight.

The same United States explosion of Covid-19 cases that helped Pfizer get results for its vaccine trial earlier this week is helping speed along Moderna's trial.

Moderna said on Wednesday its study has accumulated more than 53 infections, allowing a preliminary analysis of the shot's effectiveness to begin.

The shares jumped. Moderna did not predict how long it could take an independent monitoring committee to analyse the data, but said the company could get the data to the committee within days.

The company said it is still blinded to the data.

"Moderna has seen a significant increase in the rate of case identification across sites in the last week," the company said in a statement.

"As a result, the company expects the first interim analysis will include substantially more than 53 cases, the targeted trigger point for the analysis."

The preliminary data on Moderna's study is being prepared for submission to the monitoring board, it said.

The board will say whether the vaccine is effective, does not work, or that the trial should continue because the results are inconclusive.

The bet among top experts in the field is that Moderna's therapy, which uses a similar mRNA technology to Pfizer's, will likely prove to be highly effective, perhaps mirroring Pfizer's announcement earlier this week that its shot appears to be more than 90 per cent effective.

"Overall, I would expect similar results" in Moderna's trial, said Dr Drew Weissman, an immunologist and mRNA expert at the University of Pennsylvania, who helped develop key modifications used in mRNA vaccines.

"It is hard to imagine how it would be much different," according to Dr Weissman, whose lab receives research funding from BioNTech, the company partnering with Pfizer on its vaccine.

In vaccine trials, a certain number of volunteers - a percentage of which get a placebo - have to get infected in order to determine if the vaccine works.

That is easier to accomplish with the pandemic in the US hitting record infections on a daily basis.

Pfizer got a burst of results in recent weeks that pushed that trial over the line to take a first look.

Now Moderna's interim analysis could come within days.

Whatever happens in the trial - and there are no guarantees until it is done - the results are certain to have a big impact on Moderna shares, which have more than quadrupled this year in a wild roller-coaster ride.

The stock closed up 8.4 per cent in New York trading on Wednesday. The shares yesterday rose another 5 per cent in pre-market trading.

A preliminary analysis in Moderna's trial would likely have already been available if the shot was only 60 per cent effective, according to research firm Airfinity.

If the Moderna vaccine turns out to be 90 per cent effective, however, that timeline would be expanded and Moderna would be getting results around now, Airfinity said.

The more effective a vaccine is, the longer it takes for cases to add up since there would be fewer infections in the half of participants who got the vaccine rather than a placebo.

The strong similarity with the successful Pfizer vaccine is boosting confidence in Moderna's, which was developed in concert with the US National Institute of Allergy and Infectious Diseases (NIAID).

The Pfizer result "validates the mRNA platform", said Dr Anthony Fauci, director of the NIAID and the US government's top infectious disease doctor, in a call with reporters on Monday.

"Moderna is an mRNA candidate, which we would expect to have similar results."

Moderna's final-stage trial started on the same day as Pfizer's big trial in late July.

The company is slightly behind Pfizer largely due to structural differences in the trials.

BLOOMBERG