Moderna released preliminary results on Wednesday on an updated coronavirus vaccine targeting the Omicron variant, calling it “our lead candidate” to serve as a U.S. booster in the fall.
The company’s researchers tested a booster dose that combined the original vaccine with a vaccine specifically targeting Omicron, the variant that became dominant last winter. They found that among those with no evidence of previous coronavirus infection, the combination produced 1.75 times the level of neutralizing antibodies to Omicron, as the existing Moderna vaccine did alone.
While those results may seem encouraging at first glance, many experts worry that the virus is evolving so quickly that it will outpace the ability to modify vaccines, at least as long as the United States depends on human clinical trials for results.
Moderna’s new findings, from a clinical trial of 814 volunteers, indicate that the updated vaccine produced a significantly stronger immune response against Omicron than the existing vaccine one month after the booster injection was given. The booster injections followed three previous doses of Moderna’s vaccine.
But Omicron has been spawning sub-variants for months, and some vaccine experts say it now matters how well a new booster formulation would protect against the newest sub-variants, BA.4 and BA.5, and not Omicron itself. First discovered in South Africa early this year, these two subvariants now account for 13 percent of new cases in the United States and are spreading rapidly. By some estimates, they could compete with two other Omicron sub-variants, BA.2 and BA.2.12.1, which are currently dominant within a month.
Moderna has not released any data on how the updated vaccine worked against BA.4 or BA.5. In a presentation Wednesday morning, Dr. Stephen Hoge, the president of the company, that researchers are still collecting data on these and other subvariants.
But he said a very small sample, along with isolated other studies, suggested that the levels of neutralizing antibodies activated by the updated vaccine were two to three times lower against the BA.4 and BA.5 subvariants, compared to those against Omicron. But he said those levels were “still a very comfortable place,” a view echoed by at least one federal health official who reviewed the data.
Moderna officials said they couldn’t say yet whether the reconfigured vaccine will provide more durable protection than the existing one, but they hoped it would, based on previous findings from a study of a vaccine reconfigured against another. variant, which was released in April.
The latest sub-variants seem to spread even faster than previous versions of Omicron and may be better at evading the immune system’s defenses. It is unclear whether they cause more serious illness. dr. Anthony S. Fauci, the White House’s chief medical adviser, said in an interview Tuesday that South Africa, where BA.4 and BA.5 were widespread, “had seen a slight increase in hospital admissions, but the use of the ICU and the death toll remains really stable low.”
Regardless, given the rate at which the virus mutates, some vaccine experts say it makes more sense to target the most recent versions, rather than forms of the virus that have already caught up or will soon be.
The problem is, Moderna and Pfizer — the maker of the other major coronavirus vaccine in the United States — don’t have enough time right now to conduct more human clinical trials and still get shots before the fall, when the Biden administration hopes to be able to offer an updated vaccine to counter what public health experts predict will be a winter wave.
That could force regulators to choose updated vaccines based on data from lab and mouse or other animal trials, rather than robust human trials. It is also possible that another new variant or sub-variant of care will appear by the fall, further complicating the picture.
External advisors to the Food and Drug Administration will meet on June 28 to discuss which vaccine formulation would work best as a fall booster; vaccine manufacturers have said they should start production soon.
“Of course, the final decision is always left to the FDA,” said Dr. Fauci. “But what the FDA will probably do is keep as many irons on the fire as they can. And they may need to go back to alternative decision avenues, namely lab data and possible animal data.”
When asked whether Americans would accept a booster formulation without lengthy human trials, he said, “People who are really, really concerned about protecting themselves will do that.”
John Moore, a virologist at Weill Cornell Medicine in New York, said many health care professionals would feel comfortable switching to a different model for coronavirus vaccine development at this point in the pandemic, more like the one used is used to adjust the flu vaccine every year. Federal health officials said the composition of the annual flu vaccine has changed to meet new variants with minimal new human testing.
Moderna’s trial of the vaccine targeting Omicron began in late February. The mean age of the participants was 57. All volunteers had received three injections of Moderna’s existing vaccine — two injections, followed by a booster dose given an average of eight months after the second injection.
About four and a half months after that first booster, 377 volunteers received a second booster with the existing vaccine, while 437 received the booster intended to work against Omicron. The updated booster elicited a stronger immune response in both those previously infected with the virus and those who had not.
Overall, those who received the updated booster had 59 percent more neutralizing antibodies than those who received the existing booster, according to data released by Moderna.
Antibodies are the body’s first line of defense in fighting off infection from the coronavirus. Other immune responses that also defend against Covid-19 were not measured; those tests are much more complex and time-consuming to perform.
dr. Paul Burton, Moderna’s chief medical officer, described the results as very encouraging. “We really feel like this is kind of a fundamental turning point in our fight against this virus — that we can adapt to a variant,” he said.
But dr. Moore said a less than two-fold increase in neutralizing antibodies over the existing vaccine is “just a modest benefit.”
“Does that explain a change in vaccine composition, given the cost and logistics and everything else involved?” he asked. “That’s what the discussion is about.”
Pfizer and BioNTech, the German partner, are also testing an Omicron-specific vaccine and are expected to announce their results shortly.
In April, Moderna released preliminary results on a vaccine modified to attack the beta variant, first discovered in late 2020. That version of the vaccine, the company said, elicited a stronger immune response than the original formulation, not only against beta, but also the Delta and Omicron variants. Although Moderna officials said the added protection against Omicron lasted for six months, they said they expected an Omicron-specific vaccine to be a better candidate.