- Coronavirus vaccine developers can rely on smaller clinical trials involving just a few hundred volunteers to test whether updated versions of authorized shots protect against emerging viral strains, the Food and Drug Administration said Monday.
- Such studies would compare participants' immune response to vaccination with a drugmaker's original shot and with any modified formulation, offering a faster path to adapting vaccines against new variants than the large trials that counted COVID-19 cases among tens of thousands of people.
- Laboratory tests, as well as results from clinical studies in the U.K., South America and South Africa, suggest several of the vaccines that are currently authorized or in late-stage testing can still protect individuals from the variants known as B.1.1.7 and B.1.351. But the data showed weakened effectiveness against B.1.351, raising concerns of a renewed health threat from a mutating SARS-CoV-2 virus.
The rapid spread of coronavirus variants in the U.K., South Africa, Brazil, and to dozens of countries beyond, has made development of updated vaccines to counter them an urgent task.
"To contain the virus, we're going to have to contain it around the world," said Janet Woodcock, acting commissioner of the FDA, on a call with reporters Monday. "Wherever it is replicating, it is mutating. As long as there is a large amount of infection around the world, probably additional viral variants will emerge."
Drawing from its experience with vaccines for influenza, the FDA has been preparing for working with drugmakers on testing modified formulations as new variants emerge. Officials previously hinted at the path outlined in a formal guidance document published Monday, and the agency has already communicated its thinking with drugmakers.
Pfizer and Moderna, for instance, are already planning for studies to test additional or modified booster shots to account for the new variants.
Publishing Monday's guidance, Woodcock said, is both for transparency and to solicit scientific input in how best to adapt and counteract the impact variants might have on vaccines proven protective against the original SARS-CoV-2 virus.
The framework outlined by the FDA is for updating coronavirus vaccines previously cleared for emergency use, and not for vaccines that have yet to be authorized. In the U.S., only shots developed by partners Pfizer and BioNTech and by Moderna have been authorized, although a third from Johnson & Johnson is currently under review.
The agency recommends drugmakers conduct "immunogenicity" studies in both previously unvaccinated individuals, as well as people who received full doses of a company's authorized vaccine. The agency wants to see data on the neutralizing antibodies generated by both the original and modified shots, and expects developers will assess the latter for "non-inferiority."
Studies in a single age group, such as adults between ages 18 and 55, are acceptable, the FDA said in its guidance, noting that efficacy could be extrapolated to other age groups.
The agency envisions updated vaccines would be cleared through amendments to previously granted emergency use authorizations, according to the guidance.
While the guidance doesn't specify the size or length of immunogenicity studies, Peter Marks, the head of the FDA division that reviews vaccines, said on Monday's call that testing would likely require a few hundred individuals and take a few months to complete.
Marks urged companies to start these studies "sooner rather than later" to prepare for swapping in a modified vaccine should it be required. The guidance does not, however, lay out when that might be, nor who would make that kind of decision.
Currently the chief variants of concern are B.1.1.7, first detected in the U.K., and B.1.351, identified in South Africa. Laboratory testing using blood samples from vaccinated individuals has shown that Pfizer's and Moderna's shots still generate roughly equal levels of neutralizing antibodies to the variant as to the original strain.
Neutralizing antibody levels were found to be lower, however, against B.1.351, an observation that parallels findings from larger clinical trials run by J&J and Novavax in South Africa. Among study participants in the U.S., J&J's vaccine was 72% effective at preventing moderate or severe COVID-19, but only 57% effective in South Africa.
Novavax's vaccine, by comparison, was about 90% effective in a U.K. study, but only approximately 50% effective in a small South Africa-based trial.
Updating vaccines to match new, more transmissible strains may present different challenges depending on the type of technology used in each shot. Messenger RNA vaccines, like those developed by Pfizer and Moderna, are seen as easier to update, although that's not been proven yet.