Viruses naturally change over time through the process of mutation. When this happens, new variants can develop. SARS-CoV-2, the new coronavirus that causes COVID-19, is no exception to this. The genetic material of SARS-CoV-2, the coronavirus that causes COVID-19, is called ribonucleic acid (RNA). To replicate, and therefore establish infection, SARS-CoV-2 RNA must hijack a host cell and use the cell’s machinery to duplicate itself.
Errors often occur during the process of duplicating the viral RNA. This results in viruses that are similar but not exact copies of the original virus. Viruses use an enzyme called a polymerase to copy their genetic material. However, polymerases aren’t perfect, and they can make mistakes. These mistakes can result in a mutation. These errors in the viral RNA are called mutations, and viruses with these mutations are called variants. Variants could differ by a single or many mutations. Mutation rates are typically higher in RNA viruses than they are in DNA viruses. Two RNA viruses with high mutation rates that we have heard of are human immunodeficiency virus (HIV) and influenza (flu). SARS-CoV-2 is also an RNA virus, but it generally mutates more slowly than other RNA viruses.
A variant is referred to as a strain when it shows distinct physical properties. Put simply, a strain is a variant that is built differently, and so behaves differently, to its parent virus. These behavioural differences can be subtle or obvious. For example, these differences could involve a variant binding to a different cell receptor, or binding more strongly to a receptor, or replicating more quickly, or transmitting more efficiently, and so on. Essentially, all strains are variants, but not all variants are strains.
Four of the most common SARS-CoV-2 variants are what we’ve come to know as the UK variant (B.1.1.7), the South African variant (B.1.351), the Brazilian variant (P.1), and the Indian variant (B.1.617). Each contains several different mutations. Let’s look at the UK variant as an example. This variant has a large number of mutations in the spike protein, which aids the virus in its effort to invade human cells.
Some recently licensed vaccines appear to protect well against the UK variant but recent data from Novavax, Johnson & Johnson and Oxford/AstraZeneca indicates possible reduced protection against the South African variant. From what we know so far, it appears that the current vaccines may be less effective for B.1.351, the variant first identified in South Africa. This is currently an area of ongoing, intense research. Mutations to the spike protein have concerned researchers because the vaccines are designed to identify and go after the viral spike protein. The spike protein is thousands of amino acids long, so a mutation would alter only a minor piece of a large protein and hence the efficacy of the vaccine won’t be totally compromised. Consequently, scientists believe these variants won’t evade the vaccine.
It’s also important to remember that no vaccine is 100 percent effective. The Pfizer-BioNTech vaccine is 95 percent effective 7 days after the second dose. The Moderna vaccine is 94.1 percent effective 14 days after the second dose. After vaccination, it’s important to continue practicing precautions such as mask wearing, physical distancing, and hand washing.
Niranjan Koirala., M.Sc., Ph.D., Researcher
Pokhara, Gandaki Province, Nepal