Helminth infections, including schistosomiasis, are widespread in tropical and subtropical regions, where infectious diseases frequently overlap. Because these parasites influence immune function, researchers have been concerned that they might impair vaccine-induced immunity.

To address this question, the German-Swiss research team, led by scientists of the German Center for Infection Research (DZIF) at the Technical University of Munich (TUM), investigated in a mouse model, how chronic Schistosoma mansoni infection affects immune responses to two different platforms: the mRNA-based COVID-19 vaccine BNT162b2 (known as "Comirnaty") and an alum-adjuvanted recombinant SARS-CoV-2 spike protein vaccine.

Different immune responses depending on vaccine platform

The researchers observed clear differences in how the two vaccine platforms stimulated the immune system. The mRNA vaccine induced strong spike-specific antibody responses and CD4 T-cell immunity in Schistosoma-infected mice, which was comparable to that of uninfected controls. Although multifunctional CD8 T-cell responses were reduced in infected animals, overall vaccine-induced immunity remained strong. The spike protein-based vaccine also elicited robust antibody responses, but generated weaker cellular immune responses than the mRNA vaccine. Nonetheless, immune responses were also comparable in infected and non-infected mice.

"Our findings demonstrate that helminth-induced immune modulation changes certain aspects of the vaccine response but does not necessarily reduce protective immunity," says Prof. Dr. Clarissa Prazeres da Costa, a professor of infection and immunity in global health at TUM and a scientist in the DZIF central research theme Neglected Tropical Diseases. "This is encouraging, particularly for regions where parasitic worm infections are highly prevalent."

Protection against SARS-CoV-2 was maintained

To determine whether the altered immune responses affected vaccine performance, the researchers infected vaccinated mice with SARS-CoV-2. For this purpose, they used the BSL-3 infrastructure at Helmholtz Munich, a state-of-the-art biosafety facility that enables research into airborne pathogens. The results showed that both vaccine platforms effectively protected both infected and non-infected animals. Vaccinated mice showed markedly reduced viral loads and minimal lung pathology after infection, suggesting that protective immunity persisted despite chronic schistosomiasis.

"This study demonstrates that the quality of the immune response varies between vaccine platforms, yet both approaches effectively prevented severe disease in our experimental model," states DZIF virologist and co-corresponding study author, Prof. Ulrike Protzer.

Relevance to global health

More than a quarter of the global population lives with helminth infections. This makes it essential to understand how these parasites influence vaccination strategies. The new findings suggest that both mRNA- and protein-based vaccines can effectively protect against SARS-CoV-2, even in populations with prevalent helminth infections. However, the researchers note that the study was conducted in a mouse model. Further clinical studies are needed to determine if similar immune mechanisms occur in humans.