Paul Klenerman is Wellcome Trust Senior Clinical Research Fellow and Professor of Immunology at the University of Oxford. He is also Immune Theme Lead at the Oxford Biomedical Research Centre. Here, he answers some of the most pressing questions we have about coronavirus (Covid-19) and the immune system.
Do children have weaker or stronger immune systems than adults? Is there a reason they seem to be less affected by COVID-19?
Generally, very young babies have weaker immune responses than adults. They are however protected for a while by antibodies they get from their mother during pregnancy, and after that through breast milk. After that they do catch up and they make good responses to the childhood vaccines for example. It is often the case that children and adults make different responses to the same infection. Chickenpox for example is often much more severe in adults than children. In adults, especially in those who smoke, it can cause a nasty pneumonia. So the responses to Covid-19 may be a bit like that – although we don’t know the exact reasons yet.
Do pregnant women have weakened immune systems?
They are certainly tuned differently. They have to do this to prevent them making immune responses against their unborn child. This can put them at risk of infections – but they are a bit specific, not just any infection. So, for example, pregnant women can get a severe infection from a bacterium called listeria – found in unpasteurised cheeses. This is usually dealt with quite well but the risk goes up in pregnancy, also in the immune suppressed (for example after a transplanted kidney) or in the elderly.
Is there a gender difference in the immune system?
Yes. This is a fascinating area of research. Overall women look like they have better immune responses than men. For example in the case of hepatitis C, only some people are able to clear this virus when they are infected initially. But women are three times as likely to do this as men. The downside of having better immunity to viruses is that the immune system is slightly more likely to trigger off when it is not needed – causing auto-immune diseases like arthritis and lupus. It is fascinating that evolution has set up the immune system like this.
Is there a way to 'boost' the immune systems? We are told about zinc, vitamin C and vitamin D: what are your thoughts on this?
It’s an interesting question and one I get asked a lot. Deficiencies of any of these, and other vitamins and minerals, can certainly weaken the immune system. But it is quite hard to make it better than normal by taking in more. It’s not to say it could never happen, but just now we don’t normally prescribe these to otherwise healthy people. To avoid a deficiency you need to be eating a healthy diet – generally that is the best advice. Vitamin D can be a bit low in the winter months and some doctors may test for this in certain circumstances and supplement that – but it is best done with your GP.
Is exercise good for the immune system?
Yes, exercise is good for your immune system. It is obviously good for you generally, together with a healthy diet – the type recommended for protecting your heart and maintaining a good weight. Exercise stimulates a process in cells called autophagy, which encourages all the body’s cells to tidy themselves up and get rid of any unwanted waste. This makes them much more efficient and is linked to better immune function. There are probably many other beneficial effects too.
What is herd immunity? And how will it apply during the coronavirus crisis?
Good question. When enough people in the population become immune to a virus, people who are not immune are less likely to be infected. Basically the virus has to work much harder to find an uninfected person to jump to and tends to die out. Herd immunity can be created by infection or by vaccination. In the coronavirus case this is a new virus with no real protective immunity in the population so there is no herd immunity but ultimately it will build up - a vaccine would be an ideal way of creating this.
What do you think people need to understand about the immune system and Covid-19?
Covid-19 causes infection of the respiratory system – starting in the lining of the airways. Once it starts growing, the immune response is triggered and eventually the virus will be eliminated. During this process the person infected will be more or less sick – that can be quite variable. A lot of the symptoms are caused by the immune response to the virus – and are common to many infections (like influenza). Some people – it seems especially the elderly and those with other health conditions – make a poor response to the virus and it is not eliminated, instead, continuing to grow. If it spreads into the lung tissues it can create substantial damage and that is when it can be lethal. This is the same process with other viruses like influenza. The difference is that usually with seasonal influenza there is some partial immunity and also a vaccine.
If you get Covid-19, are you immune to it afterwards?
If it works like other viruses, then yes. Usually, once a virus is eliminated you have immune memory – sets of cells that are specific for the virus and can protect you if it comes back.
Do all old people have less effective immune systems than younger people? Is that why Covid-19 is proving more fatal for the elderly?
Not all old people. But overall yes there are (very variable) changes in the immune system with age. On average, they respond less well to some vaccines for example. The reason why this virus is worse in the elderly is partly because of that and partly because some of those infected also have other health conditions associated with ageing, so they are less able to cope with the infection
The Immune System: A Very Short Introduction by Paul Klenerman is published by OUP Oxford
This advice was up-to-date as it was published on 13 March, 2020 at 3pm.