Vaccination reduces the likelihood of new variants emerging

By Stuff reporter

The Whole Truth: Covid-19 Vaccination | By Stuff reporter Rachel Thomas. Image credit: Hingyi Khong/Stuff


Since Covid-19 first emerged in December 2019, more than 7000 single mutations of the virus have been detected through genome sequencing in the United States alone. 

Viruses mutate constantly, just like living cells. While this might sound alarming, these changes are normal, and often meaningless. Most of the changes don’t stick, or make the virus weaker, and the mutation dies.

But sometimes a mutation gives the virus an advantage, making it more resistant to mitigation efforts and a new strain or variant emerges. This is what we’ve seen with Delta, which has become the most dominant variant around the world. 

Large-scale research from cases in the US has found the Pfizer vaccine is 90 per cent effective against hospitalisation from Delta and 91 per cent effective against death.

However the key is in the viral load, or the amount of virus in a person, as University of Otago virologist Professor Miguel Quinones-Mateu explains. 

Anywhere a virus can set up camp and spread its viral load offers a possible source of mutation. 

If a person is vaccinated, the immune system is usually able to stop the viral load from growing, and therefore reduce the chances of the virus spreading and mutating.

The viral load has a greater risk of taking hold in immune-compromised people giving the virus a better chance of breeding mutations, even if those people have had two doses, due to their weakened immunity. The good news here is the Ministry of Health is approving a third shot of the Pfizer jab for this group.

If the virus takes hold in unvaccinated populations or immune-compromised vaccinated people, there is an increased chance of the virus adapting which would make the vaccine less effective, Quinones-Mateu says.

But it’s all a numbers game, University of Otago virologist Associate Professor Matloob Husain says, and it is unlikely mutations will arise if 90 per cent of the population is vaccinated.=

That’s because the 10 per cent may not get infected as they will be surrounded by 90 per cent vaccinated people.

“If those 10 per cent do get infected and generate some variants, those variants will not get a foothold in the 90 per cent vaccinated.” 

If everyone in a house or city has been vaccinated, the viral load can’t expand its campsite, and quickly runs out of places to go.

“In order to survive, and that mutation to remain within the population, the pressure needs to be maintained,” Quinones-Mateu says. 

Reporting disclosure statement: Professor Miguel Quinones-Mateu and Associate Professor Matloob Husain, both virologists at the University of Otago, provided expert advice for this post. It was reviewed by The Whole Truth: Covid-19 Vaccination expert panel member Dr Maia Brewerton, clinical immunologist, allergist and immunopathologist.