There are 3 reasons behind the difficulty answering that question
Many people are curious about the percentage of the population that must be vaccinated to achieve “herd immunity” as we try to manage COVID-19.
It’s a fair question. People are curious as to when lockdowns will be lifted when they will be allowed to rejoin with loved ones living abroad, when their companies will be safer, and when COVID-19 will no longer dominate the news.
Expert modellers are currently entering figures into spreadsheets and examining various scenarios to predict the level of protection that varying levels of vaccination coverage will provide. The Doherty Institute’s modelling results should be available as early as possible.
However, it’s crucial to note that determining a single magic number regarding herd immunity is challenging.
What exactly is herd immunity?
Herd immunity occurs when a population’s immunity is high enough to prevent the disease from spreading further. The word “herd immunity” is derived from the idea that buffalo creates a loop, with the strongest on the exterior sheltering the weaker and more sensitive on the inside.
Although vaccination gives direct protection against disease for each of us, herd immunity allows even unvaccinated persons to benefit from the restricted transmission pathway.
Various diseases have varying immunity thresholds. For example, the threshold of herd immunity for measles is 92%-94%. There were different estimates for COVID-19, some estimated at 85% or above.
Many people, however, are hesitant to disclose a single number. The following are three explanations for this.
- Vaccine variations, as well as the disease itself
When the infectiousness of SARS-CoV-2 (the virus that produces COVID-19) is so varied, estimating a single herd immunity statistic is challenging.
We can determine a disease’s infectiousness by looking at the reproduction number, or R0-which is the average number of persons infected by one case when no preventive measures are in place. SARS-CoV-2 ancestral strains had an R0 of 2-3, whereas Delta is predicted to be twofold as infectious, with an R0 of 4-6.
The kind of vaccination, the number of doses administered (either one or both), and the way vaccines protect the various variants all play a role.
The United Kingdom estimates reveal that two doses of Pfizer vaccination are efficient between 85% and 95% against symptomatic Alpha variant, whereas two doses of AstraZeneca are effective around 70% to 85%. The overall effectiveness of the vaccine with the Delta variant seems to be decreasing by approximately 10 percentage points.
The poorer the efficiency of the vaccine, the greater the degree of immunization/protection required to effectively reduce COVID.
- We are not yet able to cover the whole population.
In Australia, the Pfizer vaccination is now provisionally licensed for children aged 12 to 15. Even if it becomes frequently recommended for this age group, vaccinating children will take time. Even if that happens, there would still be a loophole in our population protection for young children.
Adult immunization should assist children in some ways. Where overall doses of vaccine in England for two doses are 48.5 percent, the number of infections among infants under the age of 10 decreased apparently. This is mainly because of the indirect protection provided by individual adults who have been vaccinated.
- The protection of populations will differ throughout time and space.
There is hardly a clear-cut point at which all changes for the better. Protection from vaccines in people is expected to decrease over time. With this and the emergence of new variants, boosters will almost definitely be required to maintain the protection of the populations from COVID-19.
We rarely talk about herd immunity with influenza vaccines, because the period of protection from influenza vaccination is limited. Immunity from the current season’s vaccine will be substantially less effective against the newest viral strain until the next flu season.
Protection might vary geographically between locations and population areas. Even in a country that has achieved a herd immunity threshold for immunization against measles, minor outbreaks can occur in places of lesser coverage in children or when a cohort of teens and adults were not fully vaccinated as children.
The ability to establish herd immunity is also influenced by population density and the degree to which persons in a population mix with many other people – a phenomenon known as “heterogeneity of mixing”.
A COVID vaccine for children under the age of 12 has yet to be licensed.
As more people get immunized, life will gently improve
Under these considerations, it’s reasonable that specialists frequently resist providing a single value for herd immunity.
We require extremely high immunization rates because of Delta infectiousness. Then, lives will be transformed, especially if this occurs on a worldwide scale. Australia’s border restrictions will be loosened. For individuals who have been fully vaccinated, we will most certainly see milder types of isolation, such as home isolation.
Outbreaks of COVID will take place but are less dangerous since fewer people will be vulnerable to get a serious infection. Outbreaks that affect a whole city or state will be replaced by outbreaks that affect a smaller area.
Good public health measures, such as timely contact tracking and isolation, will still be required. Immediate testing may be done more frequently in the future. Novel treatments may be discovered.
Ultimately, we must be equally concerned with worldwide coverage of vaccines as we are for local coverage. Because everyone, irrespective of resources, has a right to the liberties and safety afforded by COVID-19 protection.
And, as world leaders have stated, ” until everyone is safe, no one will be safe “.