There are about 1.2 million immunocompromised people in Britain today – the exact number depends on the precise definition. But these are people whose immune systems are compromised in some way and so they are more likely to fare worse if they catch Covid-19.

If someone tells you in March 2022 that they've had three 'primary vaccinations' followed by a booster, then you'll know that the NHS counts them as being in the immunocompromised cohort – as everyone else who wanted it have had just two 'primary vaccinations' followed by the booster.

The range of medical reasons for being immunocompromised is extremely wide. It may be because of an auto-immune disease (one in which the immune system attacks the body's own tissues), or because of a recent organ transplant, or because of a blood cancer – and many other reasons besides.

Amongst the vaccinated immunocompromised cohort there is a huge range of immune response effectiveness against Covid-19. At one end of the spectrum, it is exactly as if the person has not been vaccinated – and worse, because their immune system overall is not working properly. At the more positive end of the spectrum the person has immune responses to Covid that overlap with those of the 'normal' population. The problem is that the person involved doesn't know which end of the spectrum they're on – although their doctor might be able to give them a rough idea.

Each person's immune system is unique because every person has a unique history and a unique set of genes (yes, even identical twins can have differences in their DNA). That is an amazing thought when you stop to think about it. But it makes it difficult for immunocompromised people to know how careful to be. For them, as for many, the hardest times during a pandemic are at the beginning and near the end. At the beginning no-one really knows what's going on and immunocompromised people at that stage sometimes don't even know that they should be extra careful.

For example, in the first Covid wave in 2020, one out of every three patients with certain forms of blood cancer died after being infected with the virus. But near the end of the pandemic the problem is that many people stop taking any precautions at all, so it's hard for the immunocompromised person to travel freely in crowded conditions – or sing loudly and happily in a crowded church, when all they're thinking about is the Omicron aerosol around them.

In early March 2022, the number of new Omicron infections in the UK is around 40,000 – 60,000 per day. There are more than 10,000 people in hospital with the Omicron variant of Covid-19. The number of daily deaths of those with Covid-19 is in the range 100 – 200. Many of these are unvaccinated people, but some also are the vaccinated immunocompromised.

So if we imagine the 1.2 million immunocompromised people being evenly spread around the country, then if your congregation has 120 people present each Sunday morning, then two of them are likely to be immunocompromised (if they come to church physically!).

Back in December last year many immunocompromised people became very excited because AstraZeneca had produced a vaccination-substitute called Evusheld. This consists of two antibodies that block infection by the Covid Delta variant very effectively. The antibodies are modified to make them more stable so that they provide very effective protection against Delta for at least six months.

They are given by intramuscular jabs – just like a vaccine. Having such 'ready-made' antibodies in the body means that it's just as if that person has been vaccinated, although normal vaccination in parallel remains important also as the body's T cells need to be trained in how to resist infection.

In the USA Evusheld was very rapidly authorized for use in the immunocompromised, leading to a literal lottery in which, so far, only relatively few of the 7 million Americans in that cohort have yet been able to have the jab.

And then to complicate matters the Omicron variant also came along in December, and Evusheld is less effective in protecting against Omicron – though how much less is still being worked out.

In the UK it currently remains under consideration by the Medicines and Healthcare products Regulatory Agency [MHRA], and it's hard to know which way they will eventually jump. Without MHRA approval, no new medication can be used in this country.

So how should the Church respond to this situation, knowing that they are very likely to have some immunocompromised people in their congregations? Here are a few practical tips:

• Keep the online option going as long as you can as that will enable the immunocompromised to keep joining in services from home until the general infection levels have declined further.
• When people show up at your church still wearing a mask, they should be treated with respect and perhaps found a place to sit which is not in the most crowded area and, if at all possible, near an open window.
• Try and keep the church building well ventilated – that will make it much more likely that immunocompromised people will feel comfortable about attending.
• Church leaders shouldn't pretend to be medics, but it's quite useful if they can keep somewhat up-to-date with the latest NHS medications that might be helpful for the immunocompromised. The elderly who are still shielding at home might just not be aware of what's available and at least can be encouraged to discuss a new medication with their GP.
• General church education is useful. It's good for Christians with healthy immune systems to realise that it's not lack of faith that is preventing an immunocompromised person from coming to church, but just trying not to be stupid. It's not a question of a lack of faith when someone looks both ways before crossing the road. It's also good to remember how Satan tempted Jesus in the wilderness by telling Him to throw Himself down from the Temple because the angels "will lift you up in their hands, so that you will not strike your foot against a stone" [Matt. 4:6]. Christians have no promise from God that He will protect them from the consequences of their own stupid actions, or actions that demonstrate hubris rather than true faith.
• Having said all that, clearly fellowship and worship with other Christians is a key aspect of what being part of the body of Christ, His Church, entails. After two years of keeping away from church, it may well be hard for the immunocompromised person to start attending once more. Sympathy and understanding are important in such situations – but even more important is to take practical steps to ensure that their decision doesn't, for them, feel stupid. How high is the infection rate in your area? How much aeration does the church have in its services? How crowded is it? The immunocompromised person simply wants to keep looking both ways before crossing the road – that's all.

Dr Denis Alexander was previously Chair of the Molecular Immunology Programme at The Babraham Institute, Cambridge. He is a member of the immunocompromised cohort. He is the Emeritus Director of The Faraday Institute for Science and Religion and a contributor to its Wonders of the Living World project helping Christians engage with science.