By Nana Dadzie Ghansah
One question I hear often from doubters of the COVID-19 vaccine efforts has to do with the flu vaccine:
“How come we do not have a good flu vaccine, but in 9 months, we already have a COVID-19 vaccine?”
Blame the sneakily elusive Influenza A virus.
There are four Influenza virus types — A, B, C, and D. Out of the four types, A and B are the ones that mostly cause disease in humans. The reservoir of these viruses are usually birds, but they have also been isolated from pigs and bats.
Of the two types, Influenza A is the more virulent and the one that can cause pandemics. Type B can lead to epidemics but not pandemics. We will find out shortly why.
Like most viruses, the viruses gain access to the human cell with the help of a protein. Influenza viruses use two different proteins. They are hemagglutinin and neuraminidase. Hemagglutinin gets it into the cell, where it replicates. After replication, it needs neuraminidase to get it out to invade other cells. Hemagglutinin is the protein vaccines target.
Now the Influenza A virus has sixteen subtypes of the hemagglutinin (H1 to H16) and nine types of neuraminidase (N1 — N9) proteins. (Recently, subtypes H17 — H18 and N10- N11 were isolated from bats ).
This means for Influenza A, there are potentially 198 different subtype combinations. Luckily, only 131 subtypes have been detected in nature. In humans, the subtypes that afflict us so far are H1, H2, and H3 and N1 and N2. So, for instance, in 2009, we had an outbreak of H1N1. This was genetically different from the H1N1 that caused the 1918 pandemic. At any point in time, we could have a different combination of subtypes circulating.
Where type A has so many subtypes, Influenza B has only two genetic lineages — B/Yamagata and B/Victoria.
Another factor that makes Influenza A a problem is the nature of its genetic material. It is an RNA virus that comes with its RNA polymerase to help it replicate. The problem is that the polymerase has no proofreading function like that of SARS-CoV-2. So when there is a mutation during replication, it does not get fixed. Thus over time, the Influenza virus collects many mutations that make it…