Work continues to develop Covid-19 vaccines effective against new coronavirus variants. And some researchers are eyeing an even more ambitious goal: to create broad-spectrum vaccines protective against new types of virus - even before they emerge. Researchers have warned, however, that there are significant technical hurdles to overcome before such “pan-virus” or “pan-coronavirus” vaccines could be released. Here's what we know so far: Events in recent decades – and not just the latest pandemic – have highlighted the possible need for such widely applicable jabs. In 2002, a novel coronavirus sparked the Severe Acute Respiratory Syndrome (Sars) epidemic, while the coronavirus responsible for Middle East Respiratory Syndrome (Mers) was first identified in 2012. And the concern is that more deadly viruses could emerge. Bats, for example, play host to hundreds of coronaviruses, some of which could cross the species barrier and infect humans. Such a scenario is thought to be behind the current pandemic – and it could happen again. Writing in the journal <em>Nature </em>this week, two US-based researchers, Prof Dennis Burton and Prof Eric Topol, called for the development "pan-virus vaccines" that could be developed and deployed "before the next emerging infection becomes a pandemic". The hope is that emerging pathogens could be snuffed out before they get the change to take hold globally. “We call for an investment now in basic research leading to the stockpiling of broadly effective vaccines,” they wrote. While it took less than a year to design, test and approve a vaccine against Covid-19, no vaccines developed against Sars or Mers have ever been approved, and any new pathogens that emerge may prove harder than Sars-CoV-2 (the pathogen causing the current pandemic) to create vaccines against. So, having vaccines pre-developed that are effective against a range of coronaviruses (for example) could be a useful safety measure. Broadly neutralising antibodies, effective against multiple strains of particular types of virus (such as different strains of coronavirus or multiple types of influenza viruses) could be “first-line drugs” or be used to design vaccines. Widely applicable vaccines have been suggested before, said Prof Ian Jones, a professor of virology at the University of Reading in the UK, but they represent a “very long-term” project. He warned that it could be difficult to secure continued funding to develop them once the pandemic is over. "Even then there could be no guarantee it would work for a new virus until that virus emerged and was tested," he told <em>The National.</em> “For many viruses, the creation of a vaccine is not the time-limiting step; it is the scale-up and clinical trials, both of which would still be needed in the case of a new outbreak”. As well as the emergence of all-new strains of coronavirus, widely applicable vaccines may also help to protect against variants of the coronavirus behind the current pandemic. Vaccines recently developed appear to be less effective against the South African strain of the coronavirus in particular, causing scientists to scramble to develop tweaked vaccines or booster shots to cope with them. This highlights the potential value of having a ready-made vaccine able to cope with new variants before they evolve. Despite the challenges, efforts to develop a pan-coronavirus vaccine are already underway. Last month, VBI Vaccines, based in Massachusetts, US, provided an update on trials of two vaccine candidates, one a pan-coronavirus vaccine candidate that uses the spike proteins of Sars-CoV, Mers-CoV and Sars-CoV-2, the last of which is the pathogen causing the current pandemic. The company said that it was hoping to begin clinical trials later this year. “The Covid-19 challenge we face as an industry is two-fold: first, how do we get the ongoing pandemic under control, and second, how do we ensure long-term protection against known and emerging coronaviruses,” Jeff Baxter, the company’s president said in a statement in January. News reports have suggested that mice injected with the pan-coronavirus vaccine candidate developed antibodies effective against, not just the three coronaviruses used to design the vaccine, but also a fourth coronavirus that causes colds in people. The suggestion is that the immune system was prompted by the myriad antigens it was presented with to produce these broadly neutralising antibodies. Other ways to develop broad-spectrum vaccines are also being pursued, including by synthesising tiny nanoparticles that include sections of multiple coronaviruses. Experts acknowledge the difficulties involved in developing vaccines that have a wide spectrum of effectiveness. “If we could have a vaccine that protects against variant strains, that would be hugely helpful,” said Prof David Salisbury, former chairperson of the World Health Organisation’s Strategic Advisory Group of Experts on immunisation and former director of immunisation at the UK Department of Health. “Whether this can be the way with one single cross-protective vaccine is a huge challenge. Alternatively, we may have to vaccinate with combinations of coronavirus vaccines, like we do with flu, or against four separate strains.” With flu, people are sometimes given with a trivalent vaccine, which protects against three flu viruses, or a quadrivalent vaccine, which protects against four. With Sars-Cov-2, it is “perfectly viable” to develop a vaccine effective against variants that might emerge in future, said Prof David Taylor, professor emeritus of pharmaceutical and public health policy at University College London. The spike protein of Sars-CoV-2 latches on to the ACE2 receptor of human cells to gain entry to them, and there is a limited number of ways in which this spike protein could change and still be able to do this, said Prof Taylor. The spike protein is the part of the virus vaccines target, as they stimulate the production of antibodies that recognise it. “You could theoretically work out the options it could go to and create an escape-proof vaccine with enough different sorts of antibodies that there’s no way the virus could escape,” he said.
