Even with a vaccine, fast Covid tests will be crucial

The writer is assistant professor of population health science and policy at the Icahn School for Medicine on Mount Sinai

When it comes to clinical medicine, we value precision. But when it comes to public health testing for coronavirus, less may turn out to be more.

As infections rise, European countries find themselves at varying degrees of blockade. On Saturday, the United States got a new president-elect and counted a new daily record of 134,000 cases of Covid-19. Joe Biden has already appointed a Covid-19 task force that will work to keep the virus under control.

While it’s encouraging to read information about the vaccine from Pfizer and BioNTech, which was found to be 90% effective in a late stage study, there are no guarantees that it will stop the spread of the virus. We must also consider the logistical nightmare of distributing a vaccine that must be kept at minus 80 degrees Celsius until the injection point and requires two doses.

Short supplies (and a lack of trust) that limit absorption mean it is unlikely to protect the entire world population. Nor do we know how long immunity lasts for people who have been infected. Putting all of our eggs in one biomedical basket works against us at a time when we need not just all the tools, but all the hands on the deck.

We must continue to take other protective measures. Yet blockages and social distancing integrated by masks are blunt instruments. A better way to proceed is to identify and isolate contagious people. An effective test is essential to check for an airborne virus that spreads rapidly and often silently from presymptomatic and asymptomatic people.

The testing regimes have so far been inadequate. Covid-19 becomes contagious days before symptoms appear (if they do). But most people don’t look for a test until they feel sick, and many wait days later. Some never worry, and the asymptomatic ones slip through the net.

Even once tested, people often have to wait extra days for a result. PCR (polymerase chain reaction) tests, the gold standard of diagnostic sensitivity, cannot provide real-time results. They require specialized medical personnel to perform them and laboratory equipment to analyze them. They are also expensive. They may be ideal for DNA forensics and clinical diagnosis, but are not suitable for screening for a rapidly spreading virus.

The best alternatives are lateral flow or rapid antigen tests, which work similarly to home pregnancy tests. They are inexpensive, easy to administer on their own, give results in 15 minutes and require no laboratories. Most suitable for the pandemic are paper-based tests, designed to turn positive when someone is contagious. Such “strip” tests could be implemented cost-effectively and on a large scale to allow for frequent home testing.

Some oppose these tests because they are less sensitive than PCR. But this is not the point. A fast and frequently usable test is more useful than a highly sensitive one. Reduced sensitivity is actually an advantage, returning positive results only in those with virus levels high enough to pose a risk to others. PCR tests can be positive for weeks.

At a minimum, rapid strip tests can be used to create Covid-19-free spaces through negative test screening. In Germany, rapid tests are used to allow safe visits to loved ones in nursing homes and hospitals. In the UK, Durham University is experimenting with rapid self-administered swab tests.

In the United States, taking rapid tests on residential college campuses builds trust. Biden said it will be a priority to increase testing capacity “by many orders of magnitude,” even with home testing and instant testing. In Madrid, where rapid tests have been used for several weeks, the case rate now appears to be falling faster than in the rest of the country. Rapid antigen tests can also be readily adapted as new strains arise, as has been observed in mink in Denmark.

But the greatest potential of strip tests is their ability to stop the epidemic altogether. Testing large proportions of the population every few days would reduce the risk for everyone. Slovakia, which used rapid tests to examine two-thirds of its 5.4 million population on serial weekends, can provide evidence that mass testing can work.

Regardless of whether a vaccine is available soon or not, it’s easy to imagine how this can change the rules of the game. With Covid-19 controlled, millions of jobs would return and millions of students could go back to school. Stadiums and theaters, churches and mosques could reopen. Restaurants and pubs would be safe again. Emergency powers and intrusive surveillance apps would no longer be justified and extended lockdowns would be a thing of the past.

We could reopen our societies and keep them open.