JUST months after the coronavirus pandemic began, 10 vaccines designed to prevent covid-19 are already being tested in people, and another 114 are in development.
A vaccine that provides effective, long-lasting protection against the coronavirus would be a game-changer, far better than any treatment. 鈥淒o we need a vaccine? Absolutely we do. It鈥檚 really better to prevent,鈥� says Peter Horby, who is leading a UK trial evaluating several covid-19 treatments.
However, we don鈥檛 yet know whether it is possible to induce long-lasting coronavirus immunity with a vaccine. When people are infected by other kinds of coronaviruses, their immunity seems to fade rapidly 鈥� although subsequent infections are milder. There are concerns this could mean that any protection from a vaccine would fade too. 鈥淚t may be that we don鈥檛 get a one-dose vaccine that lasts for a lifetime,鈥� says Martin Hibberd at the London School of Hygiene & Tropical Medicine.
Advertisement
A vaccine that ensures people only become mildly ill would still be good, says Hibberd. 鈥淲e would be pretty happy with that.鈥�
Vaccines work by teaching your immune system to recognise part of a pathogen. There are a variety of ways to do this and just about every approach is being tried for the coronavirus.
Four of the 10 already being tested in people are inactivated vaccines, which administer the coronavirus in a chemically inactivated form that is unable to replicate. Another of the front runners is a subunit vaccine, consisting of the spike protein on the outside of the coronavirus, which the virus uses as a key to gain entry to our cells.
Inactivated and subunit vaccines tend not to provoke a big immune response, so chemicals often have to be added to boost their effects. Many vaccines we use today are one of these two types, including many flu vaccines.
The other five front runners use various methods 鈥� such as fatty droplets or the shell of another virus 鈥� to deliver genetic code for a viral protein, such as the spike protein, to human cells. This RNA or DNA code is then used by the cells to make the protein. Using DNA or RNA for vaccines in this way is a relatively new idea, and none has yet been approved for any disease.
None of the coronavirus vaccines currently in trials are live attenuated vaccines. This kind of vaccine uses a mutated version of the virus that is only capable of causing very mild disease, if any symptoms at all, and is the method used for many of the most effective vaccines we have, including the measles, mumps and rubella vaccines that are usually given together. Two groups in India are working on live attenuated coronavirus vaccines, but experimental vaccines of this kind have a higher risk of giving people covid-19, so it will be a while before human trials are ready to begin.
So far, the 10 experimental coronavirus vaccines that have been tested in people appear safe, based on the preliminary announcements from several teams, the fact that none of the trials have been stopped by regulators yet and one published peer-reviewed study (The Lancet, ).
For a few, there have also been studies of vaccinated people鈥檚 immune response, or tests to see if vaccinated animals are protected. These early results, most of which haven鈥檛 yet been published, suggest that these vaccines could provide at least some protection, although they have many further tests to pass yet.
Short-lived protection?
It is still far too early to pick a winner, says Danny Altmann at Imperial College London, who says different experimental vaccines will have different strengths and weaknesses. Some might not work as well in older people, for example, or provide only short-lived protection. 鈥淲e need all of these contenders,鈥� says Altmann. 鈥淲e don鈥檛 want the first, we want the best.鈥�
The only way to find out for sure how well these vaccines work is to give them to thousands of people of all ages. A University of Oxford team trialling a vaccine that uses the gene for the spike protein inside a viral shell is now expanding its initial trial of 1000 people to 10,000 people, including children and people over the age of 56. It is at this second, larger stage of human trials that vaccines usually fail, says Hibberd.
It can also take a long time to get results 鈥� and the falling numbers of new coronavirus infections in many countries will make it harder. As outbreaks decline, vaccinated volunteers are less likely to be exposed to the virus, providing less opportunity to see if it works.
This has led to proposals to deliberately infect vaccinated volunteers, to speed up the trial process. Such 鈥渉uman challenge鈥� trials would be controversial because we have no effective treatments for covid-19 yet. If the experimental vaccine doesn鈥檛 work, volunteers could die.
Advocates of the idea, such as bioethicist Nir Eyal at Rutgers University in New Jersey, if they involve young volunteers with no known health conditions who have a high risk of getting coronavirus. For the average person in their twenties, the risk of dying from covid-19 is less than 1 in 3000. The idea seems to be gaining momentum, with more than 26,000 people worldwide volunteering via the website 1daysooner.org, but it remains to be seen if any country will allow such trials. 鈥淎t this point, I would put it only a bit over 50-50 in favour of challenge trials,鈥� says Eyal.
Such trials wouldn鈥檛 reveal whether an experimental vaccine protects the most vulnerable, however. And if you want to know whether immunity lasts for, say, a year, a trial would have to take at least that long.
Even if trials do find effective vaccines, the immense challenge of making enough doses for up to 7 billion people will be a big bottleneck. This is true even for those vaccines for which manufacturing capacity is already being created before it is even clear if they work.
No one can predict how quickly a vaccine could be made. Some kinds are much harder to manufacture than others, says Altmann, and there can be unexpected hiccups that hold up production. For instance, there is currently a global shortage of the glass vials used to store vaccine doses.
