Record numbers of people in England and Wales are testing positive for covid-19. Here’s what you need to know about how lateral flow tests work, why symptoms may linger even if a person is no longer testing positive, and how long you can test positive after you have recovered from your symptoms.

What is the current advice in the UK if you have covid-19?

Although people in England no longer legally have to self-isolate if they have covid-19 symptoms or test positive, it remains UK government advice that they should for at least five days, although they can be infectious for up to 10 days and so should avoid contact with people who are at higher risk for that period. “The focus of this new phase [of the pandemic] is on protecting those who are most at risk from the virus,” said a spokesperson for the UK Health Security Agency (UKHSA) in a statement. In Scotland, Wales and Northern Ireland, people should only stop isolating before 10 days if they have two negative results from a lateral flow test (LFT) over two days.

In England, people are no longer advised to take LFTs to check when they become negative, and the tests are no longer free for the general population, although they can be bought at pharmacies. “The fact that legally it’s not enforced anymore doesn’t mean that people shouldn’t still be careful,” says at Imperial College London.

How have the rules in England changed for children?

The UKHSA no longer advises people under 18 to get tested for covid-19, unless it is on a doctor’s advice. For those who do have a positive test, the recommended self-isolation period has been cut to . “There is some evidence that children have a shorter duration of illness compared to adults,” said UKHSA head in a statement. “Ideally children would return to school as soon as they turn lateral flow negative,” says at the University of Liverpool in the UK. “But at some point, political decisions need to be taken, over cost and priorities. Prioritising children’s education and social development is important.”

How do I count how long I have been infected?

The first day someone experiences symptoms or tests positive is counted as day zero. Someone trying to self-isolate until day five would actually stay home for six days.

Does the intensity of a line on an LFT reveal anything?

Lateral flow tests aren’t approved to be used in this way, but people usually see the line on their test changing in intensity from faint to dark, and back to faint again, over the course of their infection. Some studies do show that the intensity of the line correlates with the amount of . “These tests actually are very quantifiable based on the darkness of the line,” says of eMed, a US testing firm. But even if the line is faint, there must still be replicating virus present in someone’s body in order to be making enough protein that it gives a positive result.

Why might I still have symptoms even though I test negative?

Some symptoms may continue after someone is no longer infectious. “In general, people have a cough for a long time,” says at the University of Reading in the UK. “There are two reasons for having a cough. One is because you’re infected, and that’s causing damage, and that makes you cough. The other reason for having a cough is because your respiratory tract gets damaged by the viral infection and it’s healing.”

Can you have false positives from LFTs after a covid-19 infection?

Schools in the UK are being told by health services that children may have a positive LFT for up to three months after their infection. This is “theoretically possible but it would be very unusual”, says Buchan, who ran the first mass community study of LFTs in Liverpool. LFTs test for virus protein, which is produced by replicating virus, and so are less likely to give a false positive than PCR tests. PCRs detect the virus’s genetic material, fragments of which can remain for several weeks after there is no viable virus left.

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The UK is at war, a cold civil war. Even many scientists, who are supposed to be smart and are among the most affected by it, fail to fully appreciate the consequences. This is because we live inside our societal bubbles, either supporting or loathing Brexit. Compromise has become a dirty word even for the very people who praise their flexibility and openness.

We need to snap out of this mindset. If we don’t, things are only going to get worse, especially for UK science.

I voted remain in the 2016 Brexit referendum because I have lived and worked in many European countries and simply feel European. As a scientist, I cannot possibly appreciate the importance of keeping the imperial units some backward-looking Brexiteer “Mogglodytes” treasure. So I am alright when people have derided me as an “ungrateful immigrant” . On the other hand, I cannot support calls for a second referendum. That has led some remainers to express their “deep discontent with my lack of vision”.

Why is my personal compromise so hard to understand? I am no longer against Brexit, only because I am against the disorderly version of it we’re now sleepwalking into. Maybe the problem is that I am too much of a researcher for my own good. I try to analyse things logically rather than emotionally.

Here is the logic bit. Imagine that the UK’s new prime minister Boris Johnson and the fanatic fringe push through a no-deal or similar Brexit on 31 October. Would this stop the civil war as many hope? No chance. The 48 per cent on the losing side of the referendum will continue to feel that their views and rights have been tossed aside, that they are being treated by the victors as prisoners of war. As for science, the likely economic hardship that will follow a no-deal Brexit would be a disaster, exacerbating the loss of EU funding.

You can appreciate how bad things are going to become by looking at the recent government announcement about speedy visas for top foreign scientists. The vice chancellors of some universities welcomed the move. I got only the chills. It was never hard for high-flying scientists to get work permits anywhere. The competition for the best minds is global and fierce. The countries that offer the best research opportunities and competitive funding win it, not those who offer the easiest visas.

So why did the prime minister focus on something that is nowhere near being a top priority for UK science? Because it is a promise that requires only hot air and not a penny. Spurring truly innovative scientific research of the sort that will contribute to the UK’s economic well-being requires a more far-sighted immigration policy and, most importantly, continuous funding at a level comparable to that in the US, Germany and other developed nations.

But imagine now that a divided Parliament blocks Brexit, calls a second referendum and remainers win, as many of my colleagues hope. What a nightmare. Even moderate Brexiteers will feel utterly betrayed. The cold war will become hotter: as big a disaster for the economy, and hence science, as any no-deal scenario.

We are in a terrible impasse. The lack of smart people listening to the needs of the country, let alone science, in our populist government terrifies me even more. Three years ago, the then prime minister Theresa May had a chance to make a truce between the warring parties. She could have offered to leave the EU, as the outcome of the referendum explicitly required, but also offer a follow-up referendum on leaving the common market or the customs union or both, the options never voted on.

Enacting this compromise now could lead to a well-informed vote and orderly Brexit, whatever the outcome of the second referendum. The economy could then evolve and adjust, and science and universities would be better prepared, too. This isn’t my ideal scenario, but a compromise in the search for a better outcome for science and the country.

Parliament returns from its summer recess on 3 September, with barely eight weeks to find a compromise. But all parties to the debate are just hardening their positions. It seems that only when the economy is in ruins and everyone is worn down will they be ready for a compromise – the way civil wars tend to end. The sooner we realise there will be no winners, the better. Optimism, even baseless, is always loved but helps only political careers. Compromises and U-turns are decried, but get things sorted.

Blame game