Clover Biopharma SCB-1022 combination respiratory vaccine illustration showing protection of older adults against RSV, hMPV and PIV3.

Clover Biopharma’s RSV-hMPV-PIV3 Combination Vaccines Deliver Encouraging Phase 2 Results in Older Adults

September 8, 2026 6 Min Read

Clover Biopharmaceuticals has reported positive preliminary Phase 2 data for SCB-1022 and SCB-1033, two next-generation combination respiratory vaccines designed to protect older adults against multiple major respiratory viruses with a single shot.

The results provide an important clinical validation of Clover’s strategy of using its Trimer-Tag® platform to build multivalent protein vaccines around prefusion-stabilized F antigens — and, notably, suggest that adding a third viral target does not come at the expense of immune responses against the other components.

Shanghai-based Clover Biopharmaceuticals announced positive preliminary results from an ongoing Phase 2 study in Australia evaluating SCB-1022, which targets respiratory syncytial virus (RSV) and human metapneumovirus (hMPV), and SCB-1033, which adds protection against parainfluenza virus type 3 (PIV3). (Clover Biopharmaceuticals)

The study enrolled 420 adults aged 60 to 85 years and randomized participants to receive SCB-1022, SCB-1033 or placebo. Both candidates are protein-based vaccines built from prefusion-stabilized F, or PreF, antigens using Clover’s proprietary Trimer-Tag vaccine technology platform. (Clover Biopharmaceuticals)

Phase 2 reproduces the strong immune responses seen in Phase 1

Perhaps the most important feature of the Phase 2 readout is its consistency.

At Day 28 after vaccination, geometric mean antibody titers were generally in line with — and in some cases trended above — those observed in Clover’s earlier Phase 1 study. That matters because promising immunogenicity in a small first-in-human trial does not always hold up once a vaccine moves into a larger and more representative population.

Here, the responses remained robust across all three targeted viruses. (Clover Biopharmaceuticals)

Compared with baseline, Day 28 neutralizing-antibody geometric mean fold rises (GMFRs) were:

Viral target	Day 28 neutralizing-antibody response
RSV	~6–9× increase
hMPV	~6–8× increase
PIV3	>3× increase overall
PIV3 — low baseline titers	~5× increase

The PIV3 response is particularly interesting. Among participants whose baseline PIV3 neutralizing-antibody levels were in the lowest tertile, responses rose by approximately five-fold. Clover said this was driven by increases of as much as ~20-fold in PIV3 PreF-specific antibodies. (Clover Biopharmaceuticals)

The results broadly reproduce Clover’s earlier Phase 1 findings, where SCB-1022 and SCB-1033 generated roughly six- to eight-fold increases in RSV neutralizing antibodies, six- to nine-fold increases against hMPV, and around four-fold increases against PIV3.

Adding PIV3 did not weaken RSV or hMPV responses

For combination vaccines, generating antibodies against multiple pathogens is only part of the challenge. Developers also need to show that adding additional antigens does not dilute or suppress the immune response against the original targets.

On that front, SCB-1033 produced an encouraging result.

Clover reported no evidence of immune interference against RSV or hMPV when the PIV3 PreF antigen was added to create the three-component SCB-1033 vaccine. RSV and hMPV neutralizing-antibody responses remained comparable between SCB-1033 and the two-component SCB-1022. (Clover Biopharmaceuticals)

That finding could prove important for the broader Trimer-Tag platform. If Clover can repeatedly combine multiple PreF antigens without sacrificing immunogenicity, the technology could potentially support increasingly broad respiratory vaccines rather than requiring separate vaccinations against individual pathogens.

Strong responses also held up in adults 75 and older

Another encouraging finding was the absence of an obvious age-related decline in immune response.

Participants aged 75 years and older showed antibody responses comparable to those seen in adults aged 60–74, according to Clover. (Clover Biopharmaceuticals)

This is clinically relevant because immune responses to vaccination can weaken with advancing age — precisely the population in which RSV and other lower respiratory infections can have their greatest consequences.

A combination vaccine that maintains immunogenicity into the 75+ age group could therefore have practical advantages if the program eventually demonstrates protection against disease in larger efficacy studies.

An intriguing — but very preliminary — respiratory infection signal

Clover also reported an exploratory observation that deserves attention, although it needs to be interpreted cautiously.

During the first 28 days following vaccination, the combined SCB-1022 and SCB-1033 groups experienced an approximately 62% lower rate of reported respiratory tract infections compared with placebo. The study took place during a period of substantial RSV circulation in Australia, with hMPV and PIV also circulating. (Clover Biopharmaceuticals)

That number should not be viewed as a 62% vaccine-efficacy result.

The infections were identified through adverse-event reporting, and the study did not conduct PCR sequencing to establish which viruses caused individual infections. The trial was primarily designed to assess immunogenicity and safety rather than provide a definitive estimate of protection against laboratory-confirmed respiratory disease. (Clover Biopharmaceuticals)

Still, the observation provides an interesting clinical signal that could help inform the design and powering of subsequent trials.

Safety remains favorable

The safety profile also appears supportive of further development.

Both SCB-1022 and SCB-1033 were generally well tolerated. Solicited local and systemic adverse events during the first seven days were mostly mild and transient, with fatigue, headache and injection-site pain among the most frequently reported events.

These events lasted an average of roughly two days, and unsolicited adverse events through Day 28 occurred at similar frequencies in the vaccine and placebo groups.

Importantly, Clover reported no vaccine-related serious adverse events, adverse events of special interest, or adverse events leading to discontinuation. (Clover Biopharmaceuticals)

Why Clover is pursuing a three-virus respiratory vaccine

RSV has already become a major commercial vaccine category for older adults, but RSV represents only part of the respiratory disease burden.

Human metapneumovirus can cause serious lower respiratory disease, particularly among older adults and other vulnerable populations, while PIV3 is another important cause of respiratory illness for which no widely available licensed vaccine currently provides routine protection.

Clover’s strategy is therefore broader than competing solely in the RSV market.

SCB-1022 combines RSV + hMPV, while SCB-1033 extends the concept to RSV + hMPV + PIV3. Both use prefusion-stabilized F proteins, which are designed to present viral fusion proteins in the conformation most relevant for eliciting potent neutralizing antibodies. (Clover Biopharmaceuticals)

The ultimate commercial proposition is straightforward: instead of vaccinating against one respiratory pathogen at a time, a single multivalent vaccine could potentially provide broader seasonal protection to older adults.

Trimer-Tag moves beyond proof of concept

The Phase 2 results are also important for Clover beyond these two individual vaccine candidates.

The company’s Trimer-Tag platform is designed to produce trimeric proteins that mimic the natural structure of biologically important targets. SCB-1022 and SCB-1033 give Clover an opportunity to demonstrate that the platform can accommodate multiple complex PreF antigens in the same vaccine while retaining strong immune responses.

Clover has now observed broadly consistent RSV and hMPV immunogenicity across Phase 1 and Phase 2, while the three-component SCB-1033 has so far shown no obvious immune-interference penalty from adding PIV3.

That makes this readout as much a validation of the platform as it is a milestone for the individual programs.

Manufacturing scale-up adds another piece to the story

Clover also disclosed a less eye-catching but strategically important development: the company has successfully scaled production of the RSV, hMPV and PIV3 Trimer-Tagged PreF antigen components to 2,000-liter commercial-scale bioreactors.

Multiple batches have been produced at this scale. (Clover Biopharmaceuticals)

For vaccine programs, manufacturing is often one of the biggest hurdles between encouraging clinical data and a commercially viable product. Demonstrating scalable production while clinical development is still underway could reduce some of the manufacturing risk ahead of larger late-stage studies.

What comes next?

The Phase 2 results move Clover closer to answering the larger question: can a multivalent respiratory vaccine deliver meaningful protection against several pathogens in older adults while remaining practical to manufacture and administer?

The current data cannot answer that yet. The study primarily establishes immunogenicity and safety, while definitive evidence of clinical protection will require larger and appropriately powered trials with virologically confirmed disease endpoints.

But several pieces are now lining up in Clover’s favor.

The Phase 2 immune responses broadly reproduced Phase 1 findings; responses remained strong among participants aged 75 and older; adding PIV3 did not appear to compromise RSV or hMPV immunogenicity; tolerability remained favorable; and commercial-scale antigen manufacturing has already been demonstrated.

Clover said it will now evaluate further mid- and late-stage development plans as well as potential global collaboration opportunities for the programs. (Clover Biopharmaceuticals)

That last point may be worth watching. Advancing a multivalent respiratory vaccine through large efficacy trials and into global commercialization requires substantial capital, manufacturing infrastructure and commercial reach. A development or commercialization partnership could therefore become an important part of the next phase for SCB-1022 and SCB-1033.

For now, the Phase 2 readout gives Clover something increasingly valuable in the crowded respiratory-vaccine field: evidence that its multivalent approach can generate strong immune responses against RSV, hMPV and PIV3 simultaneously without an obvious immunogenicity trade-off.