Coronavirus cases are creeping down, and so too are hospitalisations and deaths. The nation is breathing a collective sigh of relief after what feels like the longest of winters.

At the time of writing, 24 million people in the UK have been vaccinated with their first dose of either the Oxford/AstraZeneca or Pfizer/BioNTech jabs, and lockdown measures are easing slowly, with children allowed to return to school.

People are hanging onto promises made by the government of a summer free of social distancing restrictions – and some kind of return to normality by June 21. But one question hangs in the back of our minds: will cases spike again this winter, marking a return to stricter lockdown measures? 

Some experts are cautiously optimistic, while others say there’s “no doubt” there will be a further wave of infections in autumn.

Professor Sir Ian Diamond, head of the Office for National Statistics (ONS), told The Andrew Marr Show in mid-March that people “need to recognise this is a virus that isn’t going to go away” and added: “I have no doubt that in the autumn there will be a further wave of infections.”

His comments came after England’s chief medical officer Professor Chris Whitty said there were still risks to reopening society. The UK will experience another surge of cases at some point, he said.

Different models suggest different outcomes come winter. The Imperial College models predict another wave before winter, says Professor Karl Friston, an Independent Sage panellist specialising in modelling, also of University College London (UCL), while modelling from Warwick University predicts there will be no summer resurgence and a reduced wave next winter.

Modelling from University College London (UCL) furnishes long-term forecasts that are more optimistic, he adds. Namely, a suppression of viral transmission into the winter.

Whether we’ll see another locked down winter – or a restriction-free one – will depend on many factors. One is the transmissibility of the virus and its variants. There are four variants of concern in the UK: the Brazil, South Africa, Kent and so-called Bristol variants. Some are thought to increase infectiousness and others don’t respond as well to the vaccines. 

Prof Friston says if the transmission risk during the summer is substantially lower than winter, we may attain “herd immunity”. With appropriate test, trace and isolate public health measures in place to suppress local outbreaks, it may be possible to avoid a resurgence in winter.

But if viral transmission remains high during the summer – and there’s a risk of this happening restrictions ending on June 21 – herd immunity would be more difficult to achieve “and a winter resurgence is almost inevitable,” he adds.

Other factors that would influence what winter looks like include how many people take up the vaccine, or develop natural immunity, and how effective the protection from these vaccines is in real life, says Dr Julian Tang, honorary associate professor and clinical virologist at the University of Leicester.

Children most likely won’t have had the vaccine by this point, which may impact transmission, he adds. And it’s worth noting he extent of travel come autumn, which may affect the import or export of virus variants in and out of the UK. 

“From a purely virological viewpoint, with more mixing in schools, workplaces, retail, hospitality, and leisure facilities as Covid-19 restrictions are relaxed over the summer, this will allow more mixing of any existing partial vaccine escape virus variants that are already here,” says Dr Tang.

This may lead to a reduced overall vaccine efficacy and an increase in Covid-19 cases scattered across various age groups, where the vaccine response may not be optimal or where vaccine uptake has been poor.

If the vaccine rollout goes to plan, the hope is that these numbers will be relatively small and manageable for the NHS, says Dr Tang. But it will depend on the degree of circulation of partial vaccine escape variants (virus variants that have a reduced efficacy to any vaccine). Vaccines minister Nadhim Zahawi said it’ll be likely we’ll need a booster vaccine come autumn to deal with variants.

Flu is another consideration. This year has seen very low numbers, which could mean we see a spike in winter. This, in combination with Covid cases, could be a problem. Professor Rowland Kao, an expert in epidemiology and data science at the University of Edinburgh, says both flu and Covid cases will have to be kept down next winter to stop the NHS from being impacted.

Ultimately, says Dr Tang, if the Covid-19 cases are low come winter, the UK government may not impose additional restrictions. But it’s likely we’ll still see people donning face masks in public, as well as hand sanitising stations. 

If cases are high, measures may be needed while vaccines are updated to deal with any increase in the number of circulating partial vaccine escape variants. How strict will these measures will be? Only time will tell. Boris Johnson has said he wanted England’s latest lockdown “to be the last”, which suggests he might be reluctant to tighten measures to that extent again.

The uncertainty around the impact of seasonal fluctuations should be resolved over the next few months, adds Prof Friston, enabling more precise long-term forecasts as winter approaches.