One test detects signs of past infection and the other finds current viral load, also known as viral burden, which is the numerical expression of the quantity of virus in a given volume.
Researchers have revealed, that only the implementation of carefully controlled programmes that utilise two very different Covid-19 test kits will allow a sound prediction of how Coronavirus will impact a country.
Scientists have emphasised the need to understand not only where and when new cases of infection are appearing but also the need to pin point individuals who have already been infected, maybe even without realising it (which is the case with asymptomatic carriers). This will enable scientists to understand Covid-19’s behaviour over the coming months.
The tests which are needed to achieve these separate goals are:
1. Test kits which detect new infections
The detection of newly infected individuals is done using a polymerase chain reaction (PCR) test by medical staff, which will detect viral particles in a person. A PCR test will locate a particular coronavirus gene sequence and create multiple copies of it that can then easily be detected.
The PCR test is in itself very effective in detecting the virus but that efficacy depends on how well healthcare workers take samples from patients, from the nose and the back of the throat, states Andrew Preston, of Bath University.
“If a virus is not picked up on the swab, the result will be negative. Thus, how effectively the swab is taken, and the amount of virus present at the sampling sites, will determine whether the virus is detected from an infected person,” he said.
2. Test kits which detect past infections
While new infections can be tested using PCR tests, to identify individuals who have been infected in the past who should now be immune to reinfection, doctors need to use a test that will show antibodies generated in response to the past infection of Covid-19.
“Testing people across the country to find if they have been infected by Covid-19 will tell us precisely how the disease is behaving,” said Professor Adam Finn, of Bristol University. “This will create certainty about where we stand and about the measures we need to take to limit the spread of the virus. At present we are in the dark. That should stop once we get the antibody test up and running.”
Currently, the focus remains mainly on PCR testing for detecting individuals infected with Covid-19, but as the disease continues to spread, antibody tests will become more common. The UK government has already bought 3.5m antibody tests for coronavirus.