Viruses change constantly
Viruses evolve due to mutations in their genome leading to changes in the viral protein structures. The rate at which viruses mutate varies: some take more time, but for instance, the influenza virus is a good example of one that changes rapidly . Several variants of the SARS-CoV-2 virus that causes COVID-19 have also been detected.
Not all changes in viruses are significant to humans. The World Health Organization (WHO) classifies a new virus strain as a Variant of Concern (VOC) if, for example
- diagnosing the virus becomes more difficult
- the virus’s ability to cause infections increases
- the virus overcomes immunity despite vaccination or prior illness
- the disease caused by the virus becomes more severe
- the effectiveness of the treatments used is reduced
Infectiousness of the coronavirus variants and severity of the disease
Many of the coronavirus variants have been observed to be more infectious than the original strain. Some variants have also been observed to cause more severe symptoms than the original "wild type" strain. Rapid reproduction helps the virus to spread, but the increased severity of the disease it causes does not necessarily bring any advantage to the virus. If the disease leads to a rapid fatal outcome in the infected organism, the virus will not be able to spread as effectively.
Changes to the immune defence with the coronavirus variants
Coronavirus variants have been observed to affect the efficiency of the immunological defence mechanism in humans. If the coronavirus vaccine targets a specific structural part of the virus, a mutation in that part may impair the effectiveness of the vaccine. When developing coronavirus vaccines, scientists try to reduce the effects of mutations by selecting the targets to be identified with care. The situation is similar to prior illness: if one has had COVID-19 caused by a certain virus strain, a new, mutated strain may be able to bypass the immune defence gained.
Several mutations, some of them similar
The genome of a coronavirus may have several mutations. Certain types of mutations are more beneficial for the virus than others. These mutations have become common in a number of different viral strains, independently of each other. Therefore, virus variants found in different geographical areas may have similar mutations, even if their mutual origin is unknown.
Changes in viruses – and in the tests
The entire genome of the original coronavirus found in Wuhan, China in 2019 was resolved through sequencing soon after the virus was detected. The new coronavirus variants are identified by sequencing the genome of the coronaviruses found in humans and comparing it with the original.
In a PCR-based test, a sequence in the virus’s genome is selected and its presence in a sample taken from a patient is monitored. If the mutation happens to be in the selected sequence and is big enough, the test may not necessarily be able to detect the mutated virus’s genome in the sample. To ensure that new virus variants are detected, it is necessary to ensure that the PRC tests are up to date.
Coronavirus infections are also monitored through antigen-detection and antibody tests, which differ from PCR tests by their application, operating principles, sensitivity and method development processes. Test manufacturers must stay up to date regarding these tests as well, and amend them as new virus mutations emerge.
COVID-19 tests under continuous development
To detect new coronavirus variants, scientists and healthcare operators are conducting continuous and regular sequencing of virus samples. Companies developing COVID-19 tests follow and utilise this data in their product development to ensure reliable operation of the tests and to detect new virus variants. Sequencing and the development of methods is laborious, so test manufacturers must have sufficient resources for continuous and up-to-date product development. Not all testing methods can easily and rapidly be amended to match the properties of the virus mutations.
As the number of virus variants increases, the number of targets to be detected in the tests also increases. One test may not be enough to detect all virus variants – several may be needed. A certain virus variant can also become rare and even disappear from a certain area, making it less important to follow in comparison to other strains. Continuous monitoring of the virus situation and the development of test methods is vital for both the users of these tests and test manufacturers to ensure their coverage and reliability.
In addition to commercial test manufacturers, laboratories with sufficient skills and equipment carry out their own development of COVID-19 tests. It is important to monitor significant virus variants in one's own your geographical area, along with the global situation. Efficient testing of large groups of people enables an overview of the situation in the area to be maintained. This resource-intensive work is supported by commercial tests that also enable comprehensive testing of the population for new virus variants.