Norovirus Epidemic – Prospects and Vaccine Development

 

'Norovirus' (otherwise known as the 'winter vomiting bug') is the term in general use to describe the symptoms of an unpleasant stomach complaint caused by a virus. 

This isn’t a new virus, as was the causative agent of Covid i.e SARS-CoV-2. Many of us will already have been exposed to it during our lifetimes. It’s certainly not a ‘nice to have’, particularly for the very young and the elderly. The incidence is to some extent seasonal, and the virus does seem to be gaining the upper hand at present, with significant numbers catching it in UK this winter, hence the recent reports in the news media. There have been quite a few consequent hospital admissions over the last few weeks, hence the use of the term 'epidemic' in the media. The NHS is concerned about a rapid influx of new patients, at a time when it's already stretched to the limit,  if the situation continues to worsen. The recent surge in admissions hospitals are already facing due to an emerging 'flu epidemic certainly won't help.

First, a bit of background on the virus and its effects.

Noroviruses are non-enveloped, single-stranded, positive sense RNA viruses in the Caliciviridae family. Unlike Covid, which is a respiratory RNA virus, which in most people  commonly shows no or very mild respiratory symptoms, Norovirus is rarely 'symptomless'. It affects the digestive tract,  causing diarrhoea and vomiting, usually of sudden onset. Having suffered from it myself in the past, I can testify to one thing – you definitely know if you’ve got it…and there’s no escape! Fortunately most people clear the worst of the symptoms within a day or so, but if you do succumb, be prepared for at least 12-24 hours spent in obligate close proximity to a toilet bowl !

Is there a reliable vaccine available ? So far, unfortunately not – like Covid and other RNA viruses, this virus is adept at ‘changing its spots’ and new variants occur from season to season. It’s less adaptable at this than the influenza virus, however, and a single genotype, GII.4, has been responsible for more than 70% of all human outbreaks since the mid-1990s. This lack of variability may be due to its incredibly high infectiousness, making it unnecessary for it to evolve further to achieve its ends.

Consequently, in terms of medical relevance, GII.4 noroviruses are the key strains being targeted by the vaccine developers, and effective vaccines against capsid proteins and other elements of the virus should be possible. Help will thus probably be at hand eventually, and Moderna have already made good progress with an mRNA vaccine, which has now reached Phase 3. A large phase 3 long-term placebo-controlled study has already started and is scheduled to read out in 2027. Unfortunately, even if this first mRNA vaccine gets approval, it probably won't be available in UK before early 2028. Given the virus’s ability to mutate, thereafter it may be necessary to ‘top up’ immunity at frequent intervals and/or upgrade the vaccine to cope with any new variants. The mRNA ‘platform’ is ideally suited to this, as we saw with Covid vaccine evolution in the early ‘20s.  A good account of the state of vaccine development as of 2023 for those interested can be found at the following link.

For now, then, we’re ‘on our own’. As already discussed, the virus is highly infectious and transmits largely via the faecal/oral route. It has a seasonal pattern of infection, and spreads most readily when large groups of people congregate in confined spaces (e.g concerts, public transport, etc.). The virus survives on, and transmits well via, contaminated surfaces. Thus, the usual precautions of frequent hand-washing, avoiding crowded areas and exposure to 'communal' surfaces, and in some situations, wearing facemasks, should help reduce your susceptibility to infection. Self-isolation to prevent infecting others is not normally indicated – for one thing, given the symptoms, it’s very unlikely anyone with an active infection would take part in social activities, thus limiting transmission risk to those they actually live with. However, some individuals do continue shedding virus for some time after symptoms have resolved, thus it is advisable for them to refrain from actions most likely to spread infection (e.g. food preparation) for a few days after symptoms have disappeared.

Fortunately Norovirus is not usually a killer – only severe complications, usually in children under 5 and elders in their 80s and 90s are likely to present a real risk to life. Dehydration and electrolyte imbalance due potassium loss via the vomit is the main problem, and this can be readily and effectively treated by appropriate fluid supplements. The downside is that this may need to be done in hospital if IV infusions are required.

Are we immune from further infections once we’ve had the virus ? Again, unfortunately not, for the same reason – the virus is too good at infecting our GI tract, and thus there is little, if any, protective effect of pre-exposure. Norovirus is extremely infectious, with as little as 18 virus particles being required to establish itself in gut cells, which probably also contributes to the lack of antibody protection.

Thus prevention is definitely better than cure…for now, and until we get an effective vaccine.

Updates to follow....

First published 7.12.24

Revised 19.12.24