Steady march of science brings hope

That knowledge is key to the huge effort under way to develop a vaccine to stop you getting Covid-19 in the first place, and therapies to stop you getting sick or even dying should you catch it. More than 165 vaccines are being tested. We are starting to win the war when it comes to therapies, with drugs like dexamethasone keeping alive some people who would otherwise die. And more than 1,000 trials are running with a huge range of medicines, some of which will definitely help, decreasing the fear.

While all that is going on, immunologists are also trying to provide answers to one big question when it comes to Covid-19: If I have had Covid-19, then will I get it again?

Evidence in monkeys indicated the answer was no, you won't. Once monkeys were infected, scientists were unable to infect them again. Good but what about humans? Anecdotal reports suggested some people had become reinfected. These reports were hard to explain or confirm.

But now we have a chink of light in the gloom. The US's Centres for Disease Control have said there is no compelling evidence that once you've been infected, you will get infected again. And a study on a fishing vessel where there was a major outbreak has revealed that fishermen who had been infected previously did not get reinfected.

Before departure, the entire crew was tested for the virus or antibodies against the virus, both of which indicate that they would have had it. Some 104 of the 122 people on board became infected. This is known as a 'high attack rate' and reminds us how contagious Covid-19 is. Three people, however, did not test positive. And guess what? All three had tested positive for antibodies prior to departure. Those antibodies had protected them from re-infection. It's a small study that needs further scrutiny but hopeful enough for Nature, the world's leading science journal, to report on it.

If it all holds up - and remember that science is a process that can take time to reach a definite conclusion - it will also take some of the fear away. Something we badly need.

Governments need it too, as it should inform their decisions and stop them from being too draconian.

Immunologists had worried that infection might not confer protection as coronaviruses that cause the common cold don't. Previous studies had shown that people can get reinfected, although second time around, the cold is milder. The lack of protection is most likely because it is a mild disease anyway and the immune system doesn't really care about it. If Covid-19 was like that, it would mean a virus that would go on forever, just like the common cold.

Imagine that for a moment: Covid-19 forever. This would be OK if Covid-19 was like the common cold. A nuisance. But we now know that it's not like a cold in 20pc of people. It causes a much more severe disease. In those who survive, many become what are now called 'long haulers' with persistent symptoms such as chronic fatigue and so-called 'brain fog', meaning difficulty concentrating. Of those 20pc, one in five die because they are elderly or are obese or have other conditions such as heart disease.

One in three of us is in that vulnerable category. However, if infection were to mean protection, and even if it were to mean a much less severe disease next time around, then the picture would brighten.

HOPE

This is where the vaccine comes in. The history of infectious diseases on Earth tells us that most come back. There was never total immunity to measles or polio or influenza. They kept coming back. There were always children vulnerable to the viruses coming along to infect, some of whom got really sick, going deaf from measles or paralysed from polio or dying of flu. And some people got reinfected because they didn't get sick enough the first time around, mainly because the virus can switch off your immune system in order to survive.

Vaccines are, in fact, the only sure-fire way to limit infections in a population and achieve what is called 'herd immunity' - a term that only applies to vaccines and should never have been used for natural infection with Covid-19.

The vaccine is either a part of the virus or a weakened form. They've been disabled and so can't switch off our immune systems like a live virus can. And they come with a chemical called an adjuvant, which really wakes up the immune system. Like a souped-up version of the natural infection, vaccines drive antibody production, which can mop up the virus, and also T cells, a cell type in the immune system that kills cells infected with a virus. And they don't cause disease because they are not the intact virus.

If we were not able to show that natural infection can protect even a little bit, then it might mean that a vaccine would not be able to achieve this either. But now we have confidence that infection does indeed confer protection - and so we are more hopeful that a vaccine will really help. It will train the troops who will then protect you if you get infected with the real bad guy.

These initial indications that protection will endure is therefore important. Your immune system is doing what it should do: fighting the virus and then, remembering that fight, preparing it for the next fight. And the vaccine will make sure this happens in those who are vaccinated without harming them.

Memory

Something that was never a worry for immunologists was antibody levels waning after the infection. This is how it should be, otherwise your blood would be chock-full of antibodies against all the infections you've had. It's why measuring antibody levels isn't that informative. What remains are more of the cells that made them. These are called memory cells because should the infection re-emerge, then they will remember it from the first time and eliminate it. They live in your bone marrow, which is like the barracks for the troops, and they come out in their droves when you are infected again, rushing into your blood to go to your lungs and fight the virus that you have inhaled. There are also memory T cells. You won't even know you've been infected. This will happen with natural infection, as happened with those fishermen, but may not be as strong in some people who will remain infectious. It won't have happened in those not infected, 20pc of whom are at risk of severe disease or death. Hence the need for a vaccine.

This is the scenario that immunologists were hoping for, and the scientific evidence is that it is happening with Covid-19. The immune system in the protected fishermen did its job. It protected them, but more importantly, a vaccine will mean it will protect all of us, especially vulnerable people and children.

The more people we vaccinate, the lower the number of hosts for the virus to live in, bringing the viral load right down and protecting everyone. Three cheers for your immune system. And three cheers for all the immunologists doing their best to do great science that will without doubt eventually defeat Covid-19.

Luke O'Neill is professor of biochemistry in the school of biochemistry and immunology at Trinity College Dublin