Markets fell again on Tuesday following comments from the CEO of vaccine producer Moderna, suggesting that the Omicron variant of the coronavirus was likely to prove at least somewhat resilient to existing vaccines.

Markets had been picking up following dramatic plunges last Friday, after news broke of Omicron’s discovery – which caused the Dow to fall over 900 points and the FTSE 100 266 points. On Tuesday, futures tied to the Dow fell as much as 500 points at one stage before recovering a little; the FTSE fell another 75 points, and the Hong Kong stock index closed at its lowest level in over a year.

The stock jitters were occasioned by the publication of an interview in the Financial Times, in which Moderna CEO Stéphane Bancel said that the company needed another two weeks to assess its vaccine’s efficacy against the Omicron strain, and cautioned that, “There is no world, I think, where [efficacy] is the same level … we had with Delta.”

Noting the large number of mutations the new variant has on the spike protein, on which the vaccine is based, Bancel predicted a “material drop” in efficacy.

He added that if the vaccine was found to be far less effective, it would take several months to tweak it as necessary, and stressed that the decision to switch production to an Omicron-focused vaccine was not an easy one to take. He explained that there was significant risk involved in focusing solely on Omicron and moving away from other, highly prevalent variants (primarily Delta), and suggested that a better strategy might be to give more potent boosters to the elderly or those with compromised immune systems.

Albert Bourla, Pfizer’s CEO, was more upbeat when interviewed by CNBC. “Look, I’m concerned,” he said, “But we have been preparing for this … If the vaccines protect less, we need to create a new vaccine. On Friday we already started; we made our first DNA template which is the first part of the manufacturing process of a new vaccine, and we have made it clear multiple times that we will be able to have a vaccine in less than 100 days.

“In fact,” he continued, “we have already built two vaccines in less than 100 days. We built one for Delta that we didn’t end up using, because the current vaccine is very effective against Delta. We also built one for Beta which we also didn’t have to use; and now, we’re going to build one for Omicron that will only be used if we need it, if we see that the current vaccine doesn’t work.”

Bourla stressed, however, that he believed that, “Three doses of the current vaccine will keep us well protected … I don’t know if it will be equally effective at 95-plus percent against the Omicron. But I will be very surprised if we are very, very, very low.”

With regard to the future, the Pfizer CEO predicted that annual vaccinations would be the most likely scenario, “for multiple reasons: because of immunity that will be waning; because of the virus that I’m sure will be maintained around the world for years to come; and also because of variants that will emerge. I’m more confident right now that this will be the case than I was when I originally made the projection. I think we are going to have an annual revaccination, and that should be able to keep us really safe.”