New data from Moderna offer hope that booster shots against Covid-19 could become at least somewhat more effective than they already are. But the data also point to how difficult it could be to determine exactly which Covid shots to give as annual boosters.
On Tuesday Moderna released data testing a booster shot that is bivalent, meaning it contains equal amounts of vaccine from two different strains of the virus. This booster, currently known by the code number mRNA-1273.211, contains equal mRNA amounts of ancestral SARS-CoV-2 and spike proteins from the Beta variant of SARS-CoV-2, which originally emerged in South Africa. It does not contain vaccine targeted specifically against the Delta or Omicron variants that caused the most recent waves of Covid-19.
But the bivalent booster did generate levels of antibodies that blocked all recent variants — Beta, Delta, and Omicron — better than the existing Moderna Covid vaccine. “We believe that these results validate our bivalent strategy, which we announced and began pursuing in February 2021,” Moderna’s CEO, Stephane Bancel, said in a statement.
For each variant, neutralizing antibody levels for the 50 microgram dose of the booster were about twice that of the existing Moderna booster dose.
Despite the encouraging data, a preprint published alongside the company’s press release — that is, a paper that has not yet been peer reviewed by outside scientists — highlights the limitations of this study.
“The study was not designed and randomized to compare different booster candidates or dose levels head-to-head and the evaluation of booster candidates was sequential and open-label,” the authors write. Nor were measures of neutralizing antibodies generated in the laboratory at the same time.
That means it’s impossible to say whether the antibody boost provided by mRNA-1273.211 vaccine prevents infections or severe disease better than the existing booster.
At a hearing of a Food and Drug Administration advisory panel earlier this month, experts fretted about exactly how governments should make decisions about the composition of annual boosters. And they were adamant that governments, not pharmaceutical companies, should be deciding the strain composition of the shots, as the World Health Organization does for influenza shots. But these data are a reminder that those decisions can be tough. What would experts do when faced with booster shots with several different compositions? Will adding new strains work similarly for different types of vaccines? There are a huge number of open questions.
There’s also the biggest problem with annual flu shots: People don’t get them. Even with the current Covid boosters, this has been true. Data presented to the FDA panel said that 217 million Americans are vaccinated about Covid. But only 90 million people have received a booster dose. How many will turn out for a new booster next year?
Moderna isn’t moving forward with this vaccine based on these data. Instead it is conducting another study of its booster shot based on the Omicron strain — that one’s called mRNA-1273.214, with results due in the second quarter. That study appears to randomize volunteers to receive either the new booster or the original, so should give clearer data. Moderna said in its release that its goal is to “inform selection of its candidate for the Northern Hemisphere fall 2022 booster.”
Moderna did not return a request for comment on the design of its Omicron booster study.