Of the many things brought by Covid-19, there is one that has left researchers baffled: the disappearance of the classic flu, or almost.
This “oddity” is highlighted in an interesting article in the scientific journal Nature, written by Nicola Jones.
From the data available, says Jones, it appears that seasonal influenza hardly struck at all in the Southern Hemisphere, which is now past its winter, whereas the SARS-CoV-2 virus, responsible for Covid-19, has hit hard, like in the rest of the world.
Is this due to the anti-Covid measures (i.e. lockdown, masks and social distancing), which have kept even the most traditional flu viruses away?
This is likely, but not certain, because other types of respiratory viruses on the other hand, such as those of the common cold, have thrived in the Australian and New Zealand winter, and in the rest of the Southern Hemisphere. Why is this?
First of all, we have to bear in mind that rhinoviruses, which are responsible for the majority of colds, do not have a lipid coating (i.e. a coating made up of fatty molecules that can be dissolved fairly easily by soaps and disinfectants), unlike influenza viruses or SARS-CoV-2. This could be an advantage, coupled with the fact that rhinoviruses possess a greater ability to transmit asymptomatically from one person to another (so, at least, it is believed), and can therefore circulate more freely (schools).
But let’s go back to the flu viruses. Nature reports that from April to July 2020 there were astonishingly few cases of seasonal flu in Australia, Chile and South Africa. Experts detected only 51 cases of flu in more than 83,000 tests performed. Even in some South American countries that had not done such a great job of controlling Covid, the instance of influenza still remained low.
The reasons for this debacle of influenza viruses during the austral winter are still not entirely clear. Perhaps an important contribution was made by the drastic decline in travel from one country to another, which represents a significant vehicle of contagion, for all microorganisms. In addition, the strong increase in influenza vaccinations (in Australia in particular) also played a part for sure.
Experts are now wondering if something similar will happen, or is already happening, even in the Northern Hemisphere, with possible implications that are unprecedented.
First and foremost, this situation would make it much more difficult to identify the strains to put in the 2021 flu vaccine (researchers start working to prepare this type of drug many months in advance). Furthermore, Nature adds, a low-flu season could make less common variants of the disease disappear permanently but, at the same time, could also leave room for other more resistant and aggressive forms in the coming years.
All these doubts, however, lead to a final disturbing understanding: despite the very long history that links humans to colds and flu, the viruses that cause these ailments are still a great mystery to us…