mRNA-based vaccines, as shown by licensed COVID-19 vaccines, are immunogenic and can offer protection from severe disease with high efficacy.1,2 With the recent approval of a novel mRNA-based vaccine against human respiratory syncytial virus (mRESVIA; Moderna, Cambridge, MA, USA) by the US Food and Drug Administration and European Medical Agency, it is clear that mRNA-based vaccines will remain part of the future vaccine landscape.

Boosting mRNA-immunised adults with ARCT-2301 induced superior immunogenicity compared with Comirnaty BA.4-5 against both Wuhan-Hu-1 and omicron BA.4/5 variant COVID-19, and elicited a higher response against omicron XBB.1.5. Both vaccines had similar tolerability profiles. Self-amplifying mRNA vaccines could provide a substantial contribution to pandemic preparedness and response, inducing robust immune responses with a lower dose of mRNA to allow wider and more equitable distribution.

In 2021, RTS,S/AS01 became the first human parasite vaccine approved by WHO for the prevention of Plasmodium falciparum malaria in children from 5 months of age living in regions with moderate to high transmission.1 The vaccine consists of the NANP-repeat and C-terminal regions of the circumsporozoite protein (CSP), the most abundant sporozoite surface antigen, fused with the hepatitis B virus surface antigen and formulated with the liposome-base adjuvant AS01.2–4 RTS,S aims to limit the ability of the parasite to infect, mature, and multiply in the liver.

Interference between passive immunity and vaccine response is clinically significant and might affect the implementation of next-generation CSP-based vaccines for young infants and mothers as well as passive immunisation with human monoclonal antibodies.

We detected OROV IgM in six of 68 newborns with microcephaly of unknown cause. One infant who died had OROV RNA and antigen in several tissues, including the brain. The possibility of OROV vertical transmission and potential fetal harm must be investigated with urgency. The evidence presented here does not completely confirm vertical transmission or congenital malformations due to OROV, but thorough case finding and detailed investigation of maternal or fetal OROV infection is a priority.

These findings provide a comprehensive assessment of Oropouche fever in Brazil and contribute to an improved understanding of the 2023–24 Oropouche virus re-emergence. Our exploratory in-vitro data suggest that the increased incidence might be related to a higher replication efficiency of a new Oropouche virus reassortant for which previous immunity shows lower neutralising capacity.

Since early 2024, an unprecedented spread of the Oropouche virus has been observed in Brazil and beyond in Latin America. Severe clinical consequences have been described, including early reports of deaths in adults with acute neurological disease and congenital infection associated with malformations, such as microcephaly. Oropouche virus is not a new pathogen. This arthropod-borne orthobunyavirus was discovered in 1955 and has three known reassortants: Iquitos virus, Madre de Dios virus, and Perdões virus, the first two of which can cause disease in humans.

As this Editorial goes to press, The Lancet Infectious Diseases is publishing two papers with early results on the pathogenic potential of Oropouche virus (OROV), which is causing an unprecedented outbreak in the Americas. While such early data are key to understand and tackle outbreaks, they come with considerable uncertainty and raise questions about how to responsibly report and publish them.

We detected OROV IgM in six of 68 newborns with microcephaly of unknown cause. One infant who died had OROV RNA and antigen in several tissues, including the brain. The possibility of OROV vertical transmission and potential fetal harm must be investigated with urgency. The evidence presented here does not completely confirm vertical transmission or congenital malformations due to OROV, but thorough case finding and detailed investigation of maternal or fetal OROV infection is a priority.