Boris Johnson delivered the government’s coronavirus action plan under the new “delay” phase, flanked by the UK’s chief medical officer, Chris Whitty, and chief scientific adviser, Sir Patrick Vallance, on Thursday. Here are the next steps in different areas, and the justifications they gave for them.

Schools



While school closures can be effective in the case of a flu pandemic, large-scale shutdowns are not thought to be an obvious next step in dealing with the virus in the UK, the government said. Closures would have to be at least 13 weeks long to reduce the peak of Covid-19 by 10-15%. Measures such as self-isolation for seven days for those with symptoms, as advised by the government, have been modelled and are shown to be much more effective. Experts also believe it would be difficult for school closures to work in practice, as children off school would end up socialising anyway or spending time with grandparents, who would be worse-affected by the virus. Schools will be asked to stop foreign trips.

Self-isolation



The updated guidance asks people to self-isolate at home for seven days if they have one or both of a new, persistent cough (one that continues over three or four hours), and a temperature of 37.8C and above. These are considered to be mild symptoms of coronavirus and people do not need to ring 111 for advice unless their condition dramatically worsens, the government said. Following this advice is thought to be an effective way of reducing the peak number of cases by up to 20%. The seven-day period is based on people being infectious just as their symptoms start to show and for a week afterwards. In the future, the government may ask a whole household to isolate for two weeks if one person is affected.

Mass gatherings



The government believes that banning large gatherings is one of the least effective measures a country can take, reducing the peak of the coronavirus by less than 5%. The virus is just as likely to spread within a smaller group such as those watching football in the pub as it would in a large crowd. Scotland has taken a different decision, banning events of more than 500 people from Monday to free up emergency services.

Older people



The illness especially affects elderly people. Most people experience five days of a viral illness but a small proportion of people, including older people and those with underlying health conditions, may have a far more serious immune response. At the moment, individual care homes will make their own decisions based on frequent government advice on how to best to protect residents. The government accepts that both care homes and nursing homes will be difficult to defend from the virus as people circulate in and out of hospital so frequently. The overall mortality rate is 1% but could be higher among elderly people.

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Public fatigue



Experts have warned consistently about the importance of not moving ahead too quickly with dramatic lifestyle changes to try to deal with the virus. Anything too onerous suggested by the government – such as a two-week isolation period for a whole household – might be adopted enthusiastically for a few weeks but then people get bored and leave their homes just as the peak of the illness hits, the government fears. A complete and immediate “lockdown” on movement could suppress the virus for a short time but it would return once measures are lifted, the government believes. Instead, the aim is to push the peak back toward the summer months and bring in more stringent measures down the line.

Flights



Donald Trump has banned citizens from 26 European Schengen area countries from travelling to the US for 30 days. The decision will not be replicated in the UK following the advice of the chief medical officer and chief scientific adviser. The measure is not effective unless 95% of flights are stopped, the government said, when in reality only 50% stoppage is likely to be achievable. If you are to fly, the World Health Organization guidance suggests the highest-risk area is the two rows in front, behind or next to an infected person.

Testing



There will now be a shift in testing. The contain phase was about isolating individual cases, getting a diagnosis and then “contact-tracing” the people they have spent time with and asking them to self-isolate. Many people will no longer be tested if they are showing mild symptoms. Instead, those with the most serious symptoms will be given a blood test in a hospital, and the NHS will move into a phase of prioritising the most seriously ill.

The peak



Scientists and medics are using this phrase a lot, and it means the highest potential rate of cases. For the UK, the peak is expected to fall in three months’ time, likely in the summer months, and tail off throughout the autumn, the government said. Vallance said that the UK is around four weeks behind Italy, where there have been 1,000 deaths and more than 15,000 cases. The peak also brings the biggest period of challenge for the NHS. There are 5,000 ventilated beds but the service is looking to increase that number. Without a cure, the main treatment is oxygen therapy, which can be provided through a mask, and the NHS is looking to increase supplies.

• This article was amended on 13 March 2020. Updated guidance asks people to self-isolate at home if they have either or both of the following symptoms, not only both as an earlier version said: a new and persistent cough, and a temperature of 37.8C and above. This has been corrected.