Scimex: A vaccine for norovirus may be available in the future, thanks to new
research by US scientists. The researchers have developed a candidate
vaccine that boosts the body's defences against a broad range of
norovirus strains.
A multivalent candidate vaccine elicits broad antibody responses to a
range of norovirus strains, including strains not included in the
vaccine or previously encountered by participants, according to a new
study published this week in PLOS Medicine. The results of the
study, led by Lisa Lindesmith and Ralph Baric of the University of North
Carolina at Chapel Hill, indicate that a vaccine to norovirus may be
available in the future.
Worldwide, noroviruses cause one
in five cases of viral gastroenteritis. An estimated annual 300 million
cases of norovirus infection contribute to roughly 260,000 deaths,
mostly in low-income countries. Over time, noroviruses evade natural
immunity by antigenic drift, which allows them to escape from antibodies
produced in response to earlier infections.
Recent efforts to
develop a norovirus vaccine have focused on virus-like particles (VLPs),
which are constructed from molecules of the virus's capsid (outer
shell). In a phase I clinical trial, one multivalent VLP vaccine
elicited antibody generation, but did not confer immunity to the tested
strain of virus. In the current study, Lindesmith and colleagues
characterized serum specimens from ten multivalent VLP vaccine clinical
trial participants for antibodies to vaccine VLPs and also to VLPs
representing viruses that were not contained in the vaccine.
The
researchers found that VLP vaccine can rapidly elicit antibody responses
to a broad range of vaccine and non-vaccine VLPs, including to two VLPs
representing human noroviruses that they could not have previously
encountered. Overall, antibodies to norovirus strains to which
participants had previously been exposed dominated the immune response.
These
findings provide evidence that, if achieved,
VLP-vaccine-induced norovirus immunity may overcome the ability
of noroviruses to evade immunity by antigenic drift. These results must
be interpreted cautiously. The study is small, and the assays used may
not replicate how the immune system of a vaccine recipient will respond
to true norovirus infection. Additionally, the study participants were
all adults aged 18 to 49 years, while a vaccine is most needed for young
children (who account for the majority of severe infections) and the
elderly (who are most likely to die from infection). Next steps include
further development of VLP-based vaccines and additional clinical
trials. The authors state: "These data reveal new information about
complexnorovirus immune responses to both natural exposure and to
vaccination, and support the potential feasibility of an efficacious
multivalent norovirus VLP vaccine for future use in human populations."