More than 31 million people in the UK have now received their first dose of the coronavirus vaccine, with five million vaccinated with their second dose. 

Yet as we hear about the programme’s progress at home, elsewhere in Europe countries including Italy and France are facing a third wave – and we’ve been warned the same could happen here if we’re not cautious. 

“We can’t be complacent,” Boris Johnson said in a press conference on Easter Monday. “We can see the waves of sickness afflicting other countries and we’ve seen how this story goes. We still don’t know how strong the vaccine shield will be when cases begin to rise, as I’m afraid that they will – and that’s why we’re saying: please get your vaccine or your second dose when your turn comes.” 

But if so many people in the UK are vaccinated, how would a third wave even take hold? We asked three experts to explain the risk factors. 

The vaccines aren’t perfect 

Vaccination won’t completely eradicate Covid-19, explains Paul Hunter, a professor of medicine at the University of East Anglia and an expert in infectious diseases. “People generally tend to think in binaries: it stops infection or it doesn’t,” he tells HuffPost UK. “But the reality is the vaccine stops many infections but not all.” 

The vaccines available in the UK vary in whether they stop infection, stop symptomatic infection (ie. stop you getting ill), and stop severe disease, he adds. 

“All of them are pretty jolly good at stopping severe disease, but nothing is 100%. They are less good at stopping mild illness, and they’re even less good at stopping infection generally. Even if you don’t get sick – if you have an infection that is asymptomatic – you can still spread the infection on.” 

Professor Gabriel Scally, a public health physician and member of Independent SAGE (which provides independent science advice to the government and public), adds that a vaccine’s effectiveness is sometimes greater in medical trials than it is “in the field”. 

“When a vaccine [is] operationalised, there’s usually a decline in effectiveness because of a whole range of things, such as how the vaccine is handled and what temperature it’s stored at,” he explains. Although that decline is likely to be small, it’s one of a number of factors that could increase the risk of a third wave. 

Not everyone is vaccinated 

Although the UK’s vaccine programme is ahead of many other countries, there’s still a long way to go – and this is another major third wave risk factor. 

“Virus spread is mostly driven by lack of immunity and so far under-50s are still largely non-immune,” explains Dr Julian Tang, a consultant virologist and expert in respiratory sciences at the University of Leicester.

“If the vaccination has not reached those susceptible (non-immune) before further social mixing is allowed, case numbers could rise again.” 

We also have to take into account people who can’t – or choose not to – take the vaccine, adds Prof. Scally. This includes people who might not be able to take it because of serious allergies or because they’re pregnant. There will be some people who are ill or housebound, who haven’t had an opportunity to have the vaccine yet. And there are people who are worried about taking the vaccine, plus people who simply don’t want to take it and can’t be forced to. 

As lockdown eases, it’s likely we’ll see a “prevention paradox”, says Prof. Scally – it’s a term used when cases of a disease come from a population at low or moderate risk of that disease, rather than high risk. 

“What we’ve managed to do quite successfully is vaccinate those in the most vulnerable groups, the very elderly and those in residential care,” he explains. ”But it [the vaccine programme] hasn’t been so good in reaching ethnic minorities and there’s a real social class divide in distribution.”

If you’ve got a lot of cases among low and moderate-risk groups, that still poses a problem – even if deaths do not return to previous peaks. 

“Chile is a good example of a county that’s vaccinated a lot of people – not to the same level as the UK, but still a high level among those most at risk – and they’re having an absolutely terrible time now,” says Prof. Scally. 

Variants are a big factor

Another reason why we might be faced with a third wave despite vaccine progress is the fact that we’re dealing with a different beast to March 2020. 

“The UK variant that’s dominant now is much more infectious than the variant we were facing last year,” says Prof. Scally. “It could infect a very large number of people in a very short space of time, because that’s what we know this variant is capable of doing.”

Mutations from elsewhere in the world also pose a problem. “The more the virus is spreading, the more risk we have of some of the more dangerous variants taking hold, such as the South African variant or the Brazilian variant, which we know may be able to dodge the vaccines to some extent,” Prof. Scally adds. “Also, the more the virus takes off, the more risk we have of producing another homegrown UK variant, which could be dangerous as well.”

But don’t we keep reading reassurances that the vaccines work against mutations? Again, it’s time to forget the binary, says Prof. Hunter. 

“They are still effective and valuable, but they’re not quite as effective,” he emphasises. “It’s a gradual thing, not a cliff edge thing.”

New variants may also make things more difficult if they possess an “escape mutation,” adds Prof. Hunter.

An “escape mutation” is a mutation where a vaccine or previous infection won’t provide as much protection against you becoming ill again. 

“The one that’s circulating is called E4A4K, which is present in the South African variant, the Brazil variant and also in daughters of the Kent variant.  If you’ve got that mutation, vaccines aren’t as effective and indeed, neither is previous infection at protecting you against another illness,” says Prof. Hunter. 

“The Californian variant also has a different escape mutation than the E4A4K, and worryingly, there’s been a new variant described in India, which has both the Californian escaped mutation and the South African E4A4K escape mutation – it’s got two, which is more concerning, because  presumably vaccines would be even less effective against that, compared to those with a single mutation.”

As lockdown eases in the UK there’s the risk of escape mutations spreading, and this risk is heightened further if foreign travel is extended after May 17. 

“Of all of the things, the one I’m most worried about is that our very imperfect quarantine system will not stop dangerous variants reaching our shores,” says Prof. Scally. “If there is a summer tourist system and if people are allowed to go on foreign holidays, they may go on holiday to Spain or Portugal, for example, but the people they’ll be mixing with could have come from all over the world.” 

A third wave will look different 

When we talk about this potential third wave, we’re not necessary talking about a return to the outcomes of winter 2020 / early 2021, which can make things a little confusing. All three experts agreed it’s unlikely we’ll see a return of the horrific death figures we saw after Christmas. However, that doesn’t mean the burden on health services should be underestimated. 

“Younger adults can still get severe Covid-19, needing ICU care, and long Covid may be more frequent in younger non-immune adults if the virus starts spreading before they are vaccinated,” says Dr Tang. 

More than one million people in the UK are experiencing symptoms of long Covid, according to recent ONS figures. If infections rise as lockdown eases, the healthcare burden could shift to GPs as they work to help those impacted, predicts Dr Tang. 

“Depending on how much long Covid we start to see in this population, the burden on community services – and social/unemployment services – will need to be seen,” he says. 

Young people remain unvaccinated 

The trial of the Oxford/AstraZeneca vaccine in children has been paused while regulators investigate reports of a rare form of blood clot among adults. In the meantime, unvaccinated children “could act as a reservoir for new infections of non-immune/unvaccinated adults,” says Dr Tang. 

Prof. Scally agrees, saying more needs to be done to limit transmission between under 18s (and their adult family members) in order to avoid a third wave. 

“We still haven’t made the changes we need to make in schools about ventilation, or about creating more distance between pupils by taking over other premises and expanding school premises into playing fields with marquees and temporary buildings,” he says. “We know that it’s much less transmissible out of doors, so we should be moving classes outside as much as we possibly can and improving ventilation.”

Despite the vaccination programme, all three experts agreed Covid will certainly disrupt our lives for some time – but that its presence won’t always be so prominent. 

“At some point we’ve got to live with this and it will continue to circulate,” says Prof. Hunter. “Our grandchildren’s grandchildren will be getting Covid, but it probably won’t be any worse than the common cold by then.”