The first clues of whether a Covid-19 vaccine is effective in preventing infections among people may have already come in, a private agency tracking the process and scientific research has projected, pointing to protocols and enrolment data from American pharma company Pfizer.

The disclosure of efficacy data is being closely watched, particularly in the context of the presidential election in United States where president Donald Trump has on several occasions assured that a vaccine will be approved before the November 3 polling.

Pfizer’s is among half a dozen experimental vaccines being tested in large scale (Phase 3) human trials and, according to science informatics and analytics company Airfinity, it is projected to have had enough Covid-19 cases in the trial for its first interim analysis.

An interim analysis is when a trial reaches a preset threshold of infections – 32 in the case of Pfizer’s first of four – for researchers to review. If no fewer than 76.9% (26 out of the 32) of the infections are among those who got a placebo, the vaccine will have shown to be effective in preventing the disease as per the first analysis yardstick.

Airfinity’s projections suggest Pfizer would have hit the 32 cases threshold on September 27.

“To calculate these projected dates, we have reviewed all clinical trial data and protocols received so far, collected enrolment rates for the leading candidates as well as the Covid-19 attack rate at the locations where they are running their trials. We then use a code to estimate how long it will take to reach the required number of Covid-19 cases in the trial using all this information,” an Airfinity analyst told HT.

Pfizer’s chief executive Albert Bourla has in recent appearances said the company expects “conclusive” efficacy data to come in by October – a position experts have been wary of. On September 26, a group of 60 scientists and public health experts from top American institutions wrote an open letter to Pfizer expressing their apprehensions and urging Bourla to not apply for regulatory clearance till all safety standards have been met.

“Pfizer’s choice of 32 events is the lowest of all seen so far and has been widely criticised… there seems to be concern within Pfizer itself as the CEO has written out a company-wide email following the presidential election debate this week,” said the Airfinity analyst, adding that Pfizer’s choice of “four interim analyses in one phase III trial is unheard of in any vaccine trial”. In the e-mail to staff, Bourla said the company will not heed to political pressure and that the references to vaccine development process in the presidential debate was “disappointing”.

The US Food and Drug Administration (FDA), which will take the final regulatory decision, is scheduled to meet on October 22 to review possible licensing and approvals for Covid-19 vaccine candidates, though it is unlikely to discuss any specific candidates, according to its meeting schedule.

According to Airfinity’s projections, the next vaccine candidate to reach interim analysis threshold is Sinovac’s inactivated virus double-dose vaccine (October 22, Moderna’s mRNA-based double-dose candidate (October 25), and Oxford-AstraZeneca’s adenovirus vector single-dose candidate (November 24). Oxford-AstraZeneca is also experimenting with double dose formulations which will take longer for the data. Moderna is US-based while Oxford and AstraZeneca are from the United Kingdom.

Apart from these, US’s Johnson & Johnson, Russia’s Gamaleya institute and China’s Sinopharm and CanSino have the most watched vaccine candidates. These are among 18 vaccine candidates in Phase 2 and 3 trials. Among these, five have been given emergency authorisation for use among public or in some groups of people by Russia, China and the United Arab Emirates.