Why does the variant virus strain Delta spread faster than the original version in Wuhan?
In fact, this is related to evolution. Evolution refers to the results of random mutations or errors when the viral genome is replicated. Some of these gene mutations can bring advantages to the virus. Through the process of natural selection, copies of these favorable genes are more likely to survive to the next generation; and when viruses obtain genes from other viruses or even hosts, new virus strains can also be generated through genetic recombination. Scholars expect that as the COVID-19 epidemic continues, there will be more cases and more evolution. There will also be two situations:
- The virus will become easier to spread. An infected person may infect more people, and its basic reproduction number (R) will be higher.
- To shorten the time between an individual being infected and infecting others is to have a shorter “continuous interval.”
These two changes also explain that Delta has swept the world and replaced the original virus strain. For the virus, this change is obviously “good news”, but for the host (human), it has to deal with a stronger virus.
The R value of the virus strain originally found in Wuhan is 2–3, but the R value of Delta is at least 5-6. Therefore, the number of people infected with Delta may be at least twice that of the original version.
Hamish McCallum, Director of the Centre for Earth Health and Food Safety, Griffith University, Australia The Converstaion At the time of writing, it was pointed out that there was additional evidence that the continuous delta interval was much shorter than that of the original version. He believes that this may be related to the fact that people infected with Delta have a higher viral load than those infected with the earlier version, allowing the patient to spread faster after being infected with Delta; and the higher viral load may also cause Delta to be in the open air. It is easier to spread after brief contact with people.
Will the vaccine affect the way the virus evolves?
Regarding whether the vaccine will affect the evolution of the virus, McCallum said that the vaccine is effective for Delta but the effect is poor. Evolution theory has predicted this, because the variant virus strain that can escape the vaccine has more advantages.
Therefore, it can be expected that the competition between pharmaceutical companies and viruses will allow vaccines to try to catch up with the evolution of the virus, and have the opportunity to regularly vaccinate boosters like flu shots to prevent future variant virus strains.
McCallum also reminded that the COVID-19 vaccine can reduce the chance of an unfortunately infected person from spreading the virus to others, but it cannot completely prevent the spread. Not enough people to vaccinate will also increase the risk of virus evolution.
He explained from an evolutionary perspective that a person needs a certain viral load to spread COVID-19. If the vaccine is not 100% effective in blocking transmission, it can be expected that the virus will evolve more virulent and infect the vaccinated.
What will happen to future variant virus strains?
McCallum predicts that in the short term, Delta or other versions of SARS-CoV-2 R values will continue to increase, continuous spacing will decrease, and vaccine effectiveness will decrease, but it is unknown how big and fast these changes will occur.
The British Government’s Emergency Scientific Advisory Group (SAGE) has also recently analyzed the long-term evolution of the virus. SAGE means that there will almost certainly be “antigenic drift” of the virus, that is, the virus accumulates enough mutations to reduce the effectiveness of the current vaccine, so the booster of the improved vaccine will be indispensable.
Antigen drift may also occur through recombination with other human coronaviruses, which will require redesign of existing vaccines.
SAGE also believes that there is a real possibility of “reverse zoonosis”, that is, the situation where SARS-CoV-2 infects animals and then spreads back to humans, making SARS-CoV-2 more pathogenic to humans. SARS-CoV-2 infection of mink, cats and rodents has also occurred.
Because humans are not reproducing fast enough to accumulate enough favorable gene mutations, it is difficult to lead the virus in the evolutionary arms race. However, if the global medical system has sufficient resources, there is still a chance to protect most people from the threats of SARS-CoV-2 and Delta.
source:
The Conversation
