Four days ago, Boris Johnson was heralding a ramp-up of testing as “the way through the coronavirus puzzle”. His health secretary, Matt Hancock, was even floating the idea of immunity passports for people who could be confirmed as having recovered from the virus, so that they could return to work. But on Monday the government’s message was very different, following multiple reports that antibody tests were showing poor reliability. One government adviser, Prof Sir John Bell of Oxford University, said testing was at least a month away. Dominic Raab, the foreign secretary, said it was too early yet to be talking about an exit strategy from the lockdown. Even discussing ways out could “confuse the messaging” about the importance of sticking to physical distancing rules, he added. While ministers and their advisers might not want to discuss exit strategies openly, the Guardian here explores four options. Mass testing and contact tracing When coronavirus first reached Britain, each suspected case was tracked down and tested. Those found positive self-isolated while their recent contacts were traced and asked to do the same. The strategy was abandoned in early March when the government changed tack from containing to delaying the outbreak. The move unleashed a wave of criticism. The World Health Organization has stressed throughout that testing, contact tracing and quarantine are vital steps towards bringing the pandemic under control. “We have got to be able to show that we can go after the virus, because lockdowns alone will not work,” Dr Michael Ryan, the WHO’s director of emergencies, said last week. Hancock has talked of scaling up tests to 100,000 a day, but there has been no official commitment to contact tracing. Despite this, both are more than likely to feature in the exit strategy. Prof Neil Ferguson, whose outbreak modelling team at Imperial College London is advising the government, said this weekend that if the lockdown sufficiently reduced new cases then mass testing and contact tracing would “almost certainly” be introduced to try to keep a lid on the pandemic. The strategy has its challenges. The UK is desperately building up its testing capacity but the expansion needed is unprecedented and other countries are competing for the same equipment and chemicals. Contact tracing is labour intensive, and scientists have called on Public Health England to recruit a volunteer army to help identify potential cases. One hope is that an NHS contact tracing app can help by sending alerts to users who come into contact with infected people. But the app has already raised privacy concerns: to be effective it would require about 40 million people in the UK to sign up and share their health and location data. Herd immunity and cocooning the vulnerable In the absence of a treatment or protective vaccine, the UK’s initial approach to weathering the outbreak was to keep the most vulnerable people “cocooned” while managing the spread of infections in the rest of the population. This would build the kind of “herd immunity” that is normally created through vaccination. If more than 60% of the population developed immunity, the outbreak could be brought under control. One of the problems with the strategy is that no one knows who is vulnerable. As the deaths of doctors, nurses and young children have shown, it is not only older people or those with underlying conditions who fail to recover from the virus. This means acquiring herd immunity by letting the virus sweep through puts a staggering number of lives at risk. With the lockdown and physical distancing in place, the number of new infections should steadily fall, and unless millions of infections have gone undetected, herd immunity is unlikely to develop in the current outbreak. According to Mark Woolhouse, a professor of infectious disease epidemiology at Edinburgh University, one way out of the lockdown is to beef up protection around those who are known to be at risk. With intense testing of NHS workers, care home staff and others, the most vulnerable could be better shielded from the infection, drastically cutting the number of people who end up in intensive care. “That is where testing could really help get us out of this,” Woolhouse said. Alternating between tighter and looser lockdowns The lockdown and physical distancing are intended to spread the epidemic out so that hospitals do not face thousands of sick patients at once but rather a steadier stream over time. This “flattening of the curve” can save lives if intensive care units can treat and discharge the most seriously ill patients before new cases arrive. The Imperial College team that is modelling the outbreak found that the government may need to alternate between lockdown and looser rules, relaxing and then imposing the restrictions again if case numbers rebound as expected. This could potentially go on for months, depending on whether new antiviral drugs are found or a vaccine becomes available. “There is not going to be a cure for this, but if we can find a drug that works, and if we can give it to people early enough, you can stop them progressing to serious disease and needing a critical care bed,” said Paul Hunter, a professor in medicine at the University of East Anglia. Antibody tests and immunity passports The government has ordered 17.5m antibody home-testing kits, but none have yet proved reliable. Some senior scientists say the tests may pick up only half of those who have had the virus, in part because people with milder infections tend to have lower levels of antibodies in their blood. The poor performance appears to scupper hopes for using the tests soon to issue “immunity passports” so that the immune can return to work – an idea under active consideration in the UK and Germany. Even if accurate tests can be obtained, they may not be the “game-changer” that Johnson has claimed. No one knows whether antibodies in the blood mean full or only partial protection against the virus, nor how long any protection would last, making immunity passports a shaky reassurance. But while antibody tests might not be that useful for individuals, they could still be extremely valuable for tracking the outbreak and deciding on the best way to exit the lockdown, according to Prof Eleanor Riley, of Edinburgh University. “If antibody testing suggests that, say, 40 or 50% of the population has already been exposed, any relaxing of the social distancing rules is less likely to lead to a second wave of serious infections than if only 1% of the population has been exposed,” she said.