COVID-19 vaccine: reasons to be optimistic
THE first coronaviruses known to infect humans were discovered more than half a century ago — so why are there no vaccines against these viruses? Should we be optimistic that an effective vaccine will be developed now?
SARS-CoV-2, the recently discovered coronavirus that causes COVID-19, is similar enough to other coronaviruses, so scientists make predictions about how our immune system might deal with it. But its novelty warrants its own careful study.
Similar to Sars and Mers that cause severe acute respiratory syndrome, the novel coronavirus has emerged from animals and can cause damage to the lungs and sometimes other organs.
Why don’t we have a vaccine against other human coronaviruses? The emergence of Sars and Mers, in 2002 and 2012 respectively, were either quashed relatively quickly or affected small numbers of people.
Despite the interest from keen virologists, there was no economic incentive to develop a vaccine for these diseases as they posed a small threat at the time. Virologists with an interest in coronaviruses were struggling to secure funding for their research.
In contrast, COVID-19 has caused huge disruption around the world. As a result, at least 90 vaccines are under development, with some already in human trials.
How a vaccine works
A vaccine gives our body a harmless flavour of the virus, alerting the immune response to generate antibodies and/or cellular immunity (T cells) ready to fight the infection.
The idea is that we can then deploy a ready-made defence system next time we encounter the virus, and this spares us from severe symptoms. We know that most people who have recovered from COVID-19 have detectable antibodies in their blood.
We don’t know if these antibodies are fully protective, but a vaccine still has the potential to elicit powerful neutralising antibodies and scientists will evaluate these following vaccination.
Researchers will also look for potent T cell responses in the blood of vaccinated people. These measurements will help scientists predict the efficacy of the vaccine, and will be available before a vaccine is approved.
The best way to evaluate a vaccine, of course, is to judge how well it protects people from infection. But exposing vulnerable groups to the virus is far too risky, so most vaccines will be tested in younger people with no underlying health problems.
There are ethical considerations for deliberately infecting a healthy person with a potentially dangerous virus for a vaccine trial, and these need to be considered carefully.
In the course of a pandemic, a vaccinated volunteer may become infected with the novel coronavirus, especially if they are a healthcare worker. It will take time to gather data on protection following infection and compare them to people that received a placebo vaccine.
Vaccine challenges
The ideal vaccine should protect everyone and cause lifelong defences with a single dose. It would be quick to produce, affordable, easy to administer (nasal or oral administration) and wouldn’t need refrigeration, so non-specialists can distribute it to hard-to-reach parts of the world.
In reality, we don’t fully understand how to produce a vaccine that induces long-lived protective immunity for different viruses. For some infections, we need to administer booster vaccinations.