As airlines ground planes, cities are locked down and infection rates rise, many are asking how long the coronavirus pandemic will last. While the world has been comparatively successful in limiting previous viral outbreaks, the window to contain Covid-19 is now firmly closed. This new outbreak is in stark contrast to the spread and ultimate curbing of Severe Acute Respiratory Syndrome, which emerged in China in late 2002. Sars spread to 26 countries and resulted in 8,098 infections. But it was stamped out successfully over 18-months through measures including isolating infected individuals and airport screening. There have been no new cases since 2004. Today, the coronavirus is unlikely to be eliminated quite so quickly as it appears to spread much more easily from person to person. There are hundreds of thousands of cases in more than 175 countries and territories, causing tens of thousands of deaths. The rapidly climbing statistics make finding a vaccine for Sars-CoV-2 - to use this coronavirus's scientific name - all the more critical. Despite measures to hasten research, such as allowing tests on humans without initial animal trials, a vaccine is thought to be between about one and one-and-a-half years away. A global immunisation programme would be required for any vaccine to prove successful. “If you have a vaccine it will be a game-changer,” said Dr Bharat Pankhania, a senior consultant on communicable disease control and senior clinical lecturer at the University of Exeter in the United Kingdom. “It’s not easy to create a successful one.” Until a vaccine emerges, or in the absence of one, 40 to 70 per cent of the world’s adult population could become infected with Covid-19, according to Marc Lipsitch, a Harvard University epidemiologist. But if infected people develop long-term protection, this could result in “herd immunity”, in which a pathogen finds it harder to spread because fewer people are vulnerable. In this scenario, Covid-19 would have less impact during potential, subsequent outbreaks. However, it is still unclear if infected people will develop immunity. “If you had a sufficient number [of infected cases] in the world and they’re protected, that would be wonderful, but that’s a very long-term thing,” said Dr Pankhania. Another possibility, said Dr Pankhania, is that the virus “attenuates” or becomes less potent as it evolves. This can happen when deadlier forms die out because they kill their host, who can no longer pass on the virus. Viruses often do become less virulent, but typically not in the short term. “The ten-thousandth generation is usually less potent than the first generation. This is long term, several years. There is no hope in the first few months,” he said. Seasonal changes, such as warmer weather in temperate climates, could also reduce the volume of case numbers, it has been suggested. But it remains unclear if Covid-19 will follow this pattern seen with influenza. But the news isn’t all bad. As the UAE and other Gulf nations announce growing numbers of cases, and as western Europe faces an escalating crisis, some Asian nations including China, Singapore and South Korea have seen sharp falls in local transmissions. In South Korea, for example, the number of new cases has been falling for almost a month. In these countries, governments – employing experience from the outbreaks of Sars and Middle East Respiratory Syndrome (Mers) – acted fast. They introduced social distancing and tested those suspected of being infected before identifying and isolating social contacts when tests proved positive. “They deployed all means possible immediately,” said Dr Pankhania. “In the UK, you can deploy all means possible, but it won’t work because the virus is already in widespread circulation.” Because such strict control efforts achieved their intended results, China, for example, has been able to ease some social distancing measures. Now, most new cases in the country are from people arriving from abroad. “I feel we’re at least six months from anywhere near normal,” said Dr Pankhania. “After that it’s difficult to predict. But for the first six months I cannot see [normality returning]. “First there’s a shutdown and then, if things start to get better, there’s a ramping up, but it doesn’t start immediately.” Indeed, it may be about 18 months – when a vaccine might be in production – before people will no longer be expected to exercise some form of social distancing and carry out frequent handwashing. Over the same period, health services will to continue to have to test heavily and isolate positive cases if the number of infections is to be kept under control.
