Dive Insight:

When coronavirus vaccine development began early last year, Moderna, and the messenger RNA technology it and others had spent years researching, were unproven. Companies like Sanofi, Merck & Co and Johnson & Johnson, by comparison, were established vaccine makers with technologies that had already led to approved products.

Fast forward to April 2021 and mRNA technology has become the world’s best weapon against the pandemic. Two vaccines, from Moderna as well as BioNTech and partner Pfizer, are strongly protective against COVID-19 — while shots from Sanofi, Merck and others have either been delayed or judged too weak to advance.

Both Moderna’s and Pfizers’ shots, now given to more than 100 million people in the U.S., have proven safe with no sign of the rare clotting events that have complicated rollouts of vaccines from AstraZeneca and now J&J.

Crucially, the protection both vaccines offer has now been shown to hold up for at least six months. Two weeks ago, Pfizer and BioNTech reported their vaccine remained 91.3% effective against COVID-19 and offered near-complete protection against severe disease. On Tuesday, Moderna delivered a similarly strong result.

The findings position the developers to file for full approvals of their vaccines in the U.S., where they’re currently only cleared for emergency use. The positive data has also helped allow both to expand testing of their shots in adolescents and children. Pfizer has shown its shot works well in 12- to 15-year-olds, while a similar Moderna study is fully enrolled and should produce results this year. Clinical trials in younger children are also underway.

Neither company knows exactly how long the immunity their shots provide will last, particularly as virus variants that may diminish potency become more prevalent. It’s still unclear when booster shots may be needed, or whether they must be tailored to specific variants.

Still, Pfizer and Moderna see additional vaccinations as likely to be needed. Even after the pandemic is contained, the coronavirus could circulate “in pockets” around the globe, potentially leading to new outbreaks, said Moderna chief commercial officer Corinne Le Goff in a presentation Wednesday.

That means the coronavirus “is going to continue to evolve and seed new variants,” said Moderna president Stephen Hoge, “and if we wait until it’s too late, it would obviously be a mistake.”

Moderna is taking several steps. It’s closely monitoring emerging variants and any signs of “waning immunity,” while advancing plans to update its vaccine if necessary and working with governments to ensure access to boosters, Hoge said.

The most concerning variant appears to be B.1.351, which was first detected in South Africa and has since spread. Moderna and Pfizer expect their shots to protect against the variant, at least in the initial period following vaccination. Data Pfizer released from South Africa in April support that view.

But vaccine protection may not last as long as against other viral strains — particularly in high-risk populations — as neutralizing activity against B.1.351 is weaker, Hoge said.

Preclinical results published on the pre-print server Biorxiv on Tuesday show a booster vaccine Moderna has tailored to the B.1.351 variant increases neutralizing antibodies in mice. A multi-valent shot aimed at the original strain of the virus as well as B.1.351 was the “most effective at providing broad cross-variant neutralization,” the paper showed.

A complex Phase 2 study evaluating both of those vaccines, as well as a booster of Moderna’s original vaccine, is ongoing. Hoge said initial dosing in the trial is complete, and Moderna has begun scaling up manufacturing of booster shots.