Vaccine development

The first three RSV vaccines to reach market are forecast to become blockbuster products for their developers GSK, Pfizer and Moderna. While new U.S. guidelines could keep a lid on the market’s growth, executives at the three companies remain confident in rising sales.

In June, advisers to the Centers for Disease Control and Prevention recommended vaccination against respiratory syncytial virus most strongly in adults 75 years or older, or those between 60 and 75 years who are at risk of severe disease. The guidance replaced a prior recommendation that urged all adults 60 years or older to discuss vaccination with their physician.

The committee postponed a vote for the shot in adults aged 50 to 59 years, a group GSK is targeting with its shot. And it also did not guide adults to get revaccinated if they have already received an RSV shot.

The guidance presents a new hurdle to the three companies and has led some to scale back their market estimates. For example, analytics firm Airfinity cut its RSV vaccine sales forecast by two-thirds for 2030, trimming to $1.7 billion annually versus $4.7 billion previously.

Still, based on the CDC’s current recommendation, about 40 million people in the U.S. are eligible for vaccination, Moderna CEO Stephane Bancel noted on a company earnings call in August. 

GSK brought the first RSV vaccine, Arexvy, to the market in May last year and in 2024 has pulled in £244 million, or about $311 million, in sales. It holds about two-thirds of the retail share, according to the company’s earnings report for the second quarter. Since launch, about 8 million people aged 60 and older in the U.S. had received Arexvy out of the 85 million in that age group who are eligible.

While the new recommendations might keep vaccination rates in the 60 to 74 age group lower than originally anticipated, GSK chief commercial officer Luke Miels said uptake may only be minimally affected by the CDC guidance. For example, he noted that physicians might not withhold their own recommendations based on the ACIP’s decision.

Furthermore, Arexvy was the first RSV vaccine to gain FDA approval for the 50-to-59 age group, providing another opportunity for growth, GSK CEO Emma Walmsley said.

As for competition with the other two RSV shots on the market, Miels said Arexvy is “clearly the leader in the minds of physicians and patients,” adding that the clinical data is strongest among the three and “it’s the one you’d give your mum.”

Pfizer’s Abrysvo came up short of GSK’s shot in terms of sales with $201 million worldwide in the first half of the year. The company has requested approval for use in all adults younger than 59 in the U.S. and Europe, which would expand the drug’s reach even though older adults are considered at more risk.

Pfizer’s shot is also approved for maternal vaccination, and chief U.S. commercial officer Aamir Malik said that this could be viewed as a simpler way to package vaccines for providers.

Malik pointed out that Abrysvo is only six months into the market and that the clarified guidance from the CDC will serve to demonstrate the medical need down the road, expanding the “opportunity set.”

Pfizer’s leadership is still bullish on Abrysvo’s potential after setting a peak sales estimate at more than $2 billion back in December 2022.

“If anything, things have become more promising since the time that we gave this $2 billion, because we were all surprised how much the medical community and the recommended authorities are putting emphasis on the disease,” said Pfizer CEO Albert Bourla.

Among the three RSV vaccine makers, Moderna has the most riding on its version, called mResvia. The shot is only its second product on the market after its COVID-19 vaccine, sales of which have fallen dramatically.

Moderna’s shot gained U.S. approval in May. While CEO Stéphane Bancel acknowledged the market will likely be smaller this year than anticipated, he said the clarity provided by the guidelines could actually be a benefit for uptake among the included populations.

“Sometimes in vaccinations, you get a better reaction from the doctors and pharmacies and consumers with clear guidelines versus not as [many] guidelines with a larger population potential,” Bancel said. “It’s going to be interesting to see how the season plays out.”

Overall, with the respiratory virus season approaching, executives like Moderna’s Hoge believe a number of factors could impact the public’s reaction to the newly available RSV options, and the CDC guidance might not be as detrimental as it seems on paper.

GSK in July lowered its forecast for vaccine sales this year, citing inventory changes and shifting retail prioritization in the U.S. for its shingles shot Shingrix.

The British pharmaceutical company expects sales from its vaccines division to increase by low to mid-single digit percentages, down from the high single digit to low double-digit growth it predicted in May.

Shingrix, now one of GSK’s top products, earned 832 million pounds, or about $1.1 billion, in the second quarter, down from the first three months of the year but up year to date. Sales of Arexvy, the company’s new vaccine for respiratory syncytial virus, totaled 62 million pounds as demand eased along expected seasonal patterns.

Shingrix and Arexvy are two of GSK’s highest-profile products. Both are expected to propel growth, so the company’s downgraded forecast for its vaccine division counterbalanced what was otherwise a “beat and raise” quarter.

Overall, GSK reported sales of 7.9 billion pounds and raised its guidance for the year to growth between 7% and 9%, up from a prior range of 5% to 7%. The company also bumped up sales estimates for its specialty medicine division, which includes lucrative drugs for HIV.

For Shingrix, GSK reported that growth in Europe and other international markets was offset by a quarterly decline in the U.S., where the company faces challenges convincing harder-to-reach adults to get vaccinated. GSK estimates 37% of the over 120 million U.S. adults recommended for Shingrix have been vaccinated.

GSK expects Shingrix sales will eventually climb to more than $4 billion annually, driven by its introduction in countries other than the U.S.

Arexvy is newer and has started strong, winning two-thirds share of the market over Pfizer’s competing RSV vaccine Abrysvo. RSV infections in the U.S. and Europe occur most frequently in the fall and winter, so sales during the second quarter were expected to decline.

While sales will likely pick back up in the second half of the year, the Centers for Disease Control and Prevention this summer adjusted its recommendations to focus more strongly on adults aged 75 years or older, who are at higher risk of RSV-related disease. GSK has been working to broaden use of its shot in younger adults aged 50 to 59 years and, for that group, the CDC has not yet issued guidance.

GSK also has a new competitor in Moderna’s Mresvia, which earlier this year was approved by the Food and Drug Administration.

Months after winning approval of a new vaccine for respiratory syncytial virus, Moderna acknowledged that wresting market share from its two competitors may be more difficult than it thought.

Moderna’s RSV shot secured Food and Drug Administration clearance for older adults in late May, joining vaccines from GSK and Pfizer on the U.S. market. But uptake of Moderna’s product, called mResvia, has been slower than the biotechnology company anticipated.

“Maybe we were overly optimistic about our ability to compete in the first year of RSV,” said Moderna CFO Jamey Mock at an “R&D Day” conference held by the company Sept. 13. Looking ahead, Mock said, Moderna is being “more realistic” about the size of the RSV market and the share it anticipates holding.

Stéphane Bancel, Moderna’s CEO, cited difficulties in contracting, especially going against GSK and Pfizer, as well as the month or so it had to wait before obtaining usage recommendations from the Centers for Disease Control and Prevention.

“We were, I think, maybe naive or too optimistic about the start of the launch of RSV and I take full responsibility for it,” Bancel said.

GSK, which sells Arexvy, has dominated the RSV market since becoming the first to gain approval last year. But Pfizer and Moderna aim to establish their rival options and expand into younger age groups. Both companies plan to ask the FDA to clear their shots for use in adults aged 18 to 59 years, for instance.

In the meantime, though, Moderna again tweaked its financial guidance, forecasting on Sept. 13 between $2.5 and $3 billion in 2025 sales and pushing out its expected break-even date by two years.

Moderna also disclosed cuts to research spending and the discontinuation of several pipeline projects. The biotech plans to reduce R&D spending by $1.1 billion annually by 2027. It’s cut five programs, including two cancer treatments, a heart failure therapy and vaccine candidates for endemic human coronavirus and RSV in infants.

“As we've gone through and done our semiannual prioritization process, these [programs] didn't meet the bar for carrying forward,” said Stephen Hoge, Moderna’s president, during the conference.

Moderna is counting on expanding its respiratory disease business with a next-generation COVID-19 shot, as well as a combination influenza and COVID vaccine. A standalone flu vaccine, which Moderna will now test in a confirmatory efficacy study, would round out the company’s portfolio.

But the company expects that it will complete the majority of its planned respiratory R&D investment by 2026. Going forward, it intends to pour more resources into oncology while “pacing” investments in other vaccines and rare diseases, it told investors Thursday. It’s expecting to launch five new products by 2027.

A melanoma vaccine it’s been developing with Merck & Co. leads those efforts. Moderna also highlighted an experimental shot for cytomegalovirus that’s in late-stage testing and that some analysts believe to be a future blockbuster. A candidate for norovirus could also begin a Phase 3 trial shortly.

Still, pressure from investors is building. “Lofty financial expectations followed by guidance walk-backs” have caused shares to fall more than 40% since the start of August, wrote William Blair analyst Myles Minter. The FDA also appears unlikely to consider an accelerated approval for its Merck-partnered cancer shot, leaving a “long road” for the company to traverse, he wrote.

Leerink Partners analyst Mani Foroohar added that the cuts Moderna outlined aren’t enough to sway investor sentiment. More “are necessary to get the company back to sustainability,” Foroohar wrote on Sept. 13.

Vaccine maker GSK unveiled new data in early October showing its respiratory syncytial virus vaccine Arexvy protected older adults over three seasons against disease caused by infection.

Across the entire time period, one dose of Arexvy was 63% effective against RSV broadly, and 67% effective against severe disease, GSK said. However, the shot’s efficacy waned, falling to an estimated 48% in the third season alone.

Currently, the Centers for Disease Control and Prevention doesn’t recommend a second RSV vaccine dose. While GSK described the three-season data as evidence of the shot’s “significant health impact,” it said that “over time, revaccination is expected to be required to maintain an optimal level of protection.”

A common respiratory infection, RSV typically peaks during winter, causing the hospitalizations of approximately 100,000 to 160,000 older adults in the U.S. each year.

Arexvy was the first shot to gain U.S. approval last year. It has since been joined on market by Pfizer’s Abrysvo and, most recently, Moderna’s mResvia.

Despite the competition, GSK has so far won a dominant share of the market. The evidence it disclosed in October could further bolster its shot’s advantage.

The results come from a large Phase 3 trial that supported Arexvy’s approval. Approximately 25,000 people in 17 countries were enrolled in the study, which compared Arexvy to placebo at several time points.

Researchers calculated Arexvy’s efficacy against RSV-caused lower respiratory tract disease as 83% during the first season. That figure fell to 56% during the second season, before hitting 48% in the third. Safety data was consistent with previous results, GSK said.

In a statement, GSK’s Chief Scientific Officer Tony Wood said Arexvy is “the only RSV vaccine with efficacy and safety data available through three full seasons.”

“We will continue to provide data on longer term follow-up to help recommending bodies determine future revaccination schedules,” Wood said.

During a summer meeting, advisers to the CDC tweaked their vaccination guidance for older adults, focusing it more tightly on individuals 75 years or older, and those who are at higher risk of severe disease. 

Investors have watched CDC recommendations closely, as any change in vaccination scheduling could affect uptake. While RSV shot developers are remaining optimistic, sales are tracking lower than they did last year, as those who received one then are not recommended to get another.

The Food and Drug Administration on Oct. 23 expanded the approval of Pfizer’s RSV vaccine Abrysvo to include adults aged 18 to 59 years who are at an increased risk of disease from respiratory syncytial virus.

The vaccine was previously cleared in adults aged 60 years and older, as well as in pregnant women who are between 32 and 36 weeks gestation. With the latest expansion granted by the FDA, Pfizer claims its vaccine now holds the “broadest” indication for adults.

In June, the Centers for Disease Control and Prevention tightened its guidance for RSV vaccination in older adults, and delayed making recommendations for adults younger than 60.

The U.S. is entering the second RSV season in which vaccines for the virus are available for older adults.

Yet, despite three options on the market from Pfizer, GSK and Moderna, uptake has been slow so far this season. In a note to clients earlier in October, Jefferies analyst Michael Yee noted how vaccination is both tracking slower than last year and lower than analysts had expected.

One factor could be recommendations from the CDC, which doesn’t currently advise previously vaccinated individuals get another shot just yet. The agency also narrowed its guidance to focus on higher-risk adults who are over the age of 75 years.

The new FDA approval broadens the number of people who are eligible for Abrysvo, and could spur new uptake among younger adults who haven’t yet received a vaccine.

GSK also recently received an expanded approval of its RSV shot Arexvy in adults aged 50 to 59 years who are at an increased risk of disease.

However, it’s unclear when the CDC might update its recommendations, or whether it will urge previously vaccinated adults to eventually get another dose.

The FDA based its decision on data from a Pfizer trial dubbed MONeT, which studied adults who were at risk of RSV-related disease due to their chronic medical conditions. The company also recently disclosed fresh data from a MONeT substudy that showed vaccination led to strong immune responses in immunocompromised adults.

Pfizer plans to publish MONeT results in an academic journal and present them at a future medical meeting.

Derek Wallace was in a dengue-focused intensive care unit in Thailand in 2009 when he first saw the devastating, impact of the disease, also known as “breakbone fever.” Facing a shortage of space, children shared beds while parents slept together on mattresses tucked below. 

“That’s been the case for decades in some countries,” said Wallace, who was a clinical team leader for Sanofi's dengue vaccine studies at the time and is now president of Takeda Pharmaceutical’s global vaccine business unit. “But what’s really important is that it’s getting worse. There’s 30 times more dengue than there was 50 years ago, and there’s eight times more dengue now than there was 20 years ago.”

The mosquito-transmitted virus is among the top 10 global health threats designated by the World Health Organization. There were a record 6.43 million cases of dengue and nearly 7,000 deaths worldwide in 2023 — the largest outbreak ever recorded. Dengue is also spreading faster in places where it hasn’t before thanks to factors like climate change, urbanization and increased global travel, according to the WHO.

“Dengue is moving, and we are starting to get a ton of locally acquired dengue fever cases in the U.S., specifically in Puerto Rico, Virgin Islands and Florida,” said Katelyn Jetelina, an epidemiologist and data scientist known for a popular newsletter. “And we expect this to continue increasing over time.”

Despite the rapid global spread, there is no specific treatment for dengue, and worldwide vaccine availability is limited.

Sanofi’s Dengvaxia is currently the only FDA-approved dengue vaccine. But the company is discontinuing the shot in the third quarter of 2026 “due to low global demand for this product,” a Sanofi spokesperson said via email.

Takeda’s two-dose dengue vaccine, Qdenga, is approved in 40 countries excluding the U.S, and Takeda withdrew its U.S. application in 2023.

“Some additional data was requested that we couldn't provide,” Wallace said, but declined to provide details.

“There are no specific updates to share at this time about the timing of supplying additional data or resubmission,” a Takeda spokesperson said via email.

The vaccination challenge

Contracting most viral diseases for the first time will arm the body with antibodies that fend off subsequent infections. But that’s not the case with dengue, thanks to antibody-dependent enhancement that stems from dengue’s four closely related, but distinct, viral serotypes.

“It’s challenging because it's a very unique disease in which secondary infections are more severe than the first infections,” said Jetelina.

Sanofi’s vaccine has been controversial for this reason. Receiving Dengvaxia could act as a first dengue infection, resulting in a more severe illness after contracting the virus a second time. As a result, Dengvaxia can only be administered to people who’ve had dengue before, and people must be screened for a previous infection before getting the shot.

But that’s not how Dengvaxia’s initial Philippines rollout went — a mass vaccination program didn’t take this screening step, leading to more severe disease among some patients and potentially some deaths.

The onerous logistics of needing a pre-vaccine screening combined with a three-dose regimen — not to mention erodeing public trust in vaccines — has curbed demand for Dengvaxia so substantially that Sanofi is pulling it from the market. 

“While we have made consistent efforts to facilitate its access and the implementation of the ‘Screen & Vaccinate’ approach as recommended by WHO in 2018, uptake and demand has remained low,” the Sanofi spokesperson said. “Despite an increased prevalence of dengue in different parts of the world, there’s only one Dengvaxia immunization program in place due to the complexity of implementing this product.”

Qdenga doesn’t have these limitations. According to Takeda, the two-dose jab is “the only vaccine approved for use regardless of previous dengue exposure.” The WHO doesn’t recommend pre-vaccination screenings for Qdenga administration in settings with high dengue transmission, although local approvals may vary. Qdenga has been shown to be 61% effective against symptomatic disease and 84% effective in preventing hospitalization. Still, it’s not approved in the U. S.

Other vaccines are in development, including the single-dose Butantan–Dengue vaccine that showed positive Phase 3 results.

Dengue’s spread

These vaccination and treatment challenges only make dengue’s spread more worrisome.

“Dengue is spreading to areas where it was not prevalent, and it’s affecting more susceptible populations that have no immunity whatsoever,” said André Siqueira, head of the Dengue Global Program at the nonprofit Drugs for Neglected Diseases.

He points to southern Brazil, where dengue’s recent and rapid spread has overwhelmed health systems in an area that previously didn’t have any infections.

“What has happened the last few years in Brazil may mirror what can happen in these places where dengue transmission is still picking up,” Siqueira said.

The U. S. is one of those places. In Puerto Rico, a record-high dengue surge sparked a public health emergency in March, and in the Florida Keys, public health officials issued an alert last summer.

Dengue thrives in warm urban areas, and the mosquitoes responsible for its spread can efficiently reproduce even in small pockets of water. Therefore, a warming climate with heavier rainfalls, along with increased urbanization, are all fueling the spread. Moreover, these mosquitoes have evolved resistance to insecticides and are adapting to different conditions, including more temperate climates, Siqueira said.

That’s why public health organizations are taking action. DNDi kick-started its Dengue Alliance in 2022; the WHO launched a global strategic plan against dengue earlier this month; and Takeda partnered with the Indian pharma Biological E. Limited earlier this year to accelerate access to the vaccine in endemic areas.

But public health officials and local health systems are still racing against the clock, calling for more vaccines, dengue-specific treatments and improved diagnostics. 

“There is a perception that we’ll find one solution for dengue,” Siqueira said. “What we probably need in the most affected areas is an integrated approach.” 

The Food and Drug Administration in mid-June approved a new vaccine from Merck & Co. that protects against 21 types of the bacteria that causes pneumococcal disease.

The vaccine, cleared for use in adults 18 and older, will be sold by Merck as Capvaxive. Pneumococcal disease can lead to severe infection in the lungs or sometimes in the blood and spinal cord, when it is known as meningitis. Adults older than 65 or who have compromised immune systems are at particular risk for the disease.

Merck currently sells two pneumococcal vaccines. One, dubbed Pneumovax 23, is for adults at least 50 years of age and children older than two who are increased risk of infection. The other, Vaxneuvance, is for those aged six weeks and older.

But it’s Pfizer’s Prevnar shots that have dominanted the market. The company’s Prevnar 20 gained approval in 2021 for adults 18 years or older and is now also cleared for infants and teenagers. The vaccine protects against 20 serotypes, while Merck’s Vaxneuvance covers 15.

Capvaxive could have an edge there, as it targets 21 serotypes, including eight not covered by other shots.

“[Capvaxive] will be the first approved pneumococcal conjugate vaccine specifically designed to help protect against the serotypes that cause the majority of invasive pneumococcal disease in adults,” wrote Paula Annunziato, vice president of vaccine clinical development at Merck, in an email to BioPharma Dive. “It covers the serotypes responsible for ~84% of cases of [invasive pneumococcal disease] in adults 50 years and older.”

The comparator number for Prevnar 20 is 52%, per Merck. And according to the company, the eight unique serotypes covered by Capvaxive alone account for more than one-quarter of invasive pneumococcal disease cases in adults 50 years and older.

Merck set the price of Capvaxive at $287 per the single dose used for immunization. In a statement, Merck said most people in the U.S. would have access at no out-of-pocket cost following a CDC recommenation.

Shares in vaccine developer Vaxcyte soared in early September after the company unveiled results from a large study testing its experimental pneumococcal shot that analysts described as a best-case scenario.

Data from the Phase 1/2 trial showed Vaxcyte’s vaccine matched the effectiveness of Pfizer’s market-leading Prevnar 20 in protecting against 20 common strains of the bacteria that causes invasive pneumococcal disease, the company said.

Vaxcyte’s shot covers an additional 11 strains than Prevnar 20, for a total of 31. The company plans to advance its vaccine into a Phase 3 trial program in adults. Initial data from the first study in that program could come by 2026, Vaxcyte said.

Investors and analysts have been closely tracking Vaxcyte’s candidate. While the September results are from a mid-stage test, the stock market reaction indicated Wall Street sees it as a potential competitor to pneumococcal vaccines from Pfizer, Merck & Co. and GSK.

Pfizer, in particular, has been dominant with its Prevnar 20 shot. In an Aug. 14 note to clients, Mizuho Securities analyst Salim Syed noted how Vaxcyte could “disrupt Pfizer’s 20-year [plus] near monopoly” on an $8 billion market.

Approved in 2021 for adults 18 years or older, Prevnar 20 was more recently cleared to include use in infants and children. It has become the go-to option over others, including an earlier shot from Pfizer and two others from Merck.

New competitors have advanced, however. In June, Merck gained approval from the Food and Drug Administration for its latest shot, called Capvaxive. That vaccine protects against 21 serotypes, including eight that are not covered by other approved shots. Advisers to the Centers for Disease Control and Prevention later recommended Capvaxive in adults 65 years and older and young adults who have not previously received a shot and who have certain underlying health conditions.

While Vaxcyte’s competing product has a ways to go before reaching market, the early data has set high expectations. “Essentially, what we got today was the best-case scenario with zero misses,” Syed wrote in a September note to investors.

Vaxcyte’s study enrolled 1,015 healthy adults 50 years or older and tested three doses of the company’s shot against placebo.

The highest dose produced the strongest immune response, matching the efficacy of Prevnar 20 on all serotypes covered by that shot. Across seven of those serotypes, the immune response spurred by Vaxcyte’s product was statistically greater than those produced by Pfizer’s.

The middle and low doses also performed well against Prevnar 20, but were superior on fewer serotypes. All three doses outperformed Prevnar 20 on the 11 serotypes not covered by Pfizer’s vaccine.

Vaxcyte also said its vaccine appeared safe and tolerable. Local and systemic reactions to vaccination were “generally mild-to-moderate,” the company said, and resolved within days. There were no serious adverse events that study investigators judged to be related to the vaccine.

Pfizer and BioNTech in mid-August said a combination flu and COVID-19 shot they’ve been developing met one of its main goals in a Phase 3 trial but missed another, leaving the vaccine’s future in doubt. 

The study tested Pfizer and BioNTech’s vaccine against separately administered, marketed COVID and flu shots in more than 8,000 people between the ages of 18 and 64. While the combination vaccine spurred a comparable immune response against COVID and influenza A, it didn’t meet that mark against the “B” strain of the flu.  

As a result, two companies are “evaluating adjustments” that would improve the vaccine’s performance against influenza B while discussing next steps with health authorities.

Pfizer and BioNTech are in a race with rival Moderna to develop vaccines that can simultaneously protect against multiple respiratory viruses, hoping the convenience of one shot will spur an uptick in flagging immunizations. 

The undertaking has proven difficult, forcing the makers of mRNA shots to search for doses that are potent against multiple pathogens while minimizing side effects. The eventual financial reward is also unclear, as the timing of COVID and flu spikes aren’t currently lining up, complicating the utility of a single shot at a particular time, Evercore ISI analyst Umer Raffat wrote in a research note. 

Both groups have found trouble with influenza B viruses, which are less common than their “A” counterparts.

For example, Moderna’s initial flu vaccine struggled against influenza B before adjustments led to the success of a combination shot in a Phase 3 trial earlier this year. Pfizer last year reported a flu-only shot also failed to generate a sufficient immune response against influenza B, and in August reported similar issues with its combination vaccine. 

Those stumbles could leave the door open for Sanofi and Novavax, which this year partnered to develop a protein-based combination vaccine. Leerink Partners analyst David Risinger noted that “dose optimization is well-characterized” with those shots, potentially making their path through testing less complicated. 

Still, Pfizer and BioNTech intend to press forward with combination shots. Executives from both companies have claimed they’re committed to pursuing multi-pronged vaccines. “[The] results provide insight and direction towards achieving this goal,” said Annaliesa Anderson, Pfizer’s head of vaccine R&D, in an August statement.  

“We are dedicated to developing combination vaccines which provide broader protection against multiple respiratory diseases,” added BioNTech CEO Ugur Sahin.

They’re also still working on a vaccine only directed at the flu. A Phase 2 study of a new “trivalent” shot spurred a meaningful immune response against influenza B. By that measure, it also surpassed an existing shot against influenza A, the companies said. 

Moderna in early June said a combination flu and COVID-19 shot it’s developing met the goal of a late-stage study, eliciting higher immune responses to the two viruses than did available vaccines when tested among adults 50 years or older.

Dubbed mRNA-1083, the shot is made up of Moderna’s second-generation COVID vaccine and a candidate for influenza, which have each been tested on their own in separate trials. The company pit mRNA-1803 against Spikevax, its approved COVID vaccine, and against flu shots from drugmakers Sanofi and GSK.

Moderna said the data showed a single dose of mRNA-1083 was statistically equivalent, or “non-inferior,” to giving those vaccines together.

Moderna’s combination vaccine is key to its growth plans, but could also prove important for future vaccination efforts against two viruses that account for a substantial share of the seasonal infectious disease burden.

The company hopes its combination shot could ease the burden on healthcare workers and the public. Combination vaccines, such as the Tdap and MMR shots, can help improve adherence as well as immunization coverage. A shot like mRNA-1083, if approved, could be a more convenient option, especially among older adults who may need several shots each fall.

In Moderna’s study, mRNA-1083 was tested in two groups of 4,000 adults. In one, adults aged 65 years or older were randomly given either Moderna’s candidate, or Spikevax and Sanofi’s Fluzone together. (Fluzone is a high-dose vaccine for influenza.) The second group was made up of adults aged 50 years to 64 years who received with mRNA-1083 or Spikevax alongside GSK’s Fluarix.

MRNA-1083 was judged by trial researchers to be non-inferior the comparator vaccines in both groups, spurring higher antibody responses to the influenza strains H1N1, H3N2 and B/Victoria, as well as to SARS-CoV-2.

Advisers to the Food and Drug Administration in March recommended that flu vaccines this year be updated to include those three strains.

Moderna also tested immune responses against the B/Yamagata strain of influenza. However, that strain is no longer commonly circulating and public health agencies have recommended its removal from updated flu shots.

Moderna said most adverse events in the study were mild in severity and comparable to the profiles of the licensed vaccines used. Common side effects were injection site pain, headache, fatigue and muscle pain.

The company previously forecast its combo shot could arrive on market in the U.S. next year, a timeline that looks possible given the trial findings. Michael Yee, an analyst at Jefferies, wrote in a note to clients that, while the company’s “pipeline is progressing nicely,” Moderna’s near-term focus should be on launching its newly approved RSV vaccine and meeting its 2024 guidance.

Moderna’s RSV shot, dubbed Mresvia, was cleared by the FDA in late May for use in older adults. It’s the third to be approved, following OKs for GSK’s Arexvy and Pfizer’s Abrysvo.