COVID-19 mutant variants and herd immunity
Definitions & Key takeaways
Several different mutant variants of the COVID-19 virus (SARS-CoV-2) have been identified. Some of the known variants of the COVID-19 virus include variant B.1.351(Beta), which was first identified in South Africa in October 2020; P.1(Gamma) discovered in Japan in late 2020; and B.1.1.7 (Alpha), which was first discovered in the UK in late 2020.
The spread of new variants implies that more people will need to be vaccinated to achieve herd immunity. Herd immunity is the resistance to the spread of an infectious disease within a population, which occurs when a sufficient percentage of the population has been immunized, or vaccinated against the disease. For covid19, its currently estimated that herd immunity can be achieved if a population is vaccinated at above 66%.
This video aims to explain what is known about the different strains and how they may affect achievement of herd immunity.All viruses mutate.
As more people get infected with a virus, the virus has more opportunities to multiply and there are more chances that a mutation may occur.
A mutated virus can be considered a new strain when the virus has enough mutations to make it distinct from the original virus.
So, often new strains appear in places with uncontrolled outbreaks. The new strains can become a problem when the mutation gives the virus an advantage, such as making it easier to quickly spread or increasing the infection severity.For each of the COVID-19 variant strains, it’s likely the mutations took place within a single patient who was infected with the virus for a long period of time.Most relevant COVID-19 mutations affect the spike protein, which is a protein located on the outside of the virus that can bind to the host cell, helping the virus enter the cell.
The genetic code for the spike protein is within the “conserved” region, meaning the spike protein tends to be consistent across each new generation of the virus.
Most of the developing vaccines have been targeting proteins on the viruses, one of which is the spike protein, so alterations in the spike protein may make vaccines somewhat less effective.As of early March 2021, there are three clinically important strains of COVID-19: B.1.1.7, also called the UK strain, B.1.351, also called the South African strain, and P.1, also called the Brazilian strain.
While there are a number of other strains that exist, these three strains are clinically important because they potentially may be more contagious and more virulent than the original COVID-19 strain.B.1.1.7 was first discovered in the United Kingdom in late 2020 and contains multiple mutations, including those within the spike protein.
By December of 2020, it was reported to be present in numerous countries including the US. This strain is considered to be one of the most transmissible, and it spreads between people 25 to 40% faster than the other COVID-19 strains.
It’s still unclear why this higher transmission rate occurs, however, continued compliance of social distancing and personal protective equipment need to be taken to reduce the spread of B.1.1.7.
There is some concern that the B.1.1.7 may also have a higher rate of severe COVID-19 symptoms, as well as an increased fatality rate.
However, research supporting these concerns is very new, and more evidence needs to be collected to confirm these concerns are true.
There is also no current evidence that shows B.1.1.7 increases rates of reinfection with COVID-19 due to this strain. Studies have shown that the current COVID-19 vaccines are still effective against this strain, even with the mutation in the spike protein.
It’s also been found in samples from other countries, including the US, as of January 2021. B.1.351 has several of the same mutations that the B.1.1.7 has, however, it has enough unique mutations to be considered its own strain.
Some early research suggests convalescent plasma and the current COVID-19 vaccines may be less effective against this strain.
However, just like the vaccine studies with the B.1.1.7 strain, these are preliminary studies, and more research is needed to confirm these concerns.
That said, the current COVID-19 vaccines still show prevention of severe COVID-19 symptoms and hospitalizations.P.1. was first found in Brazilian travelers in Japan in late 2020 and continues to be a major strain within Brazil.
In the spring of 2020, the original COVID-19 strain infected 75% of the Brazilian city Manaus. It was thought by some epidemiologists that the city reached herd immunity given the high-percentage of infections in the spring.
However by December 2020, another wave of COVID-19 infections began, and the new wave was being caused by the P.1 variant strain.
The variant strain has been reported in several other countries as well and was found in the US in late January 2021. P.1.
has a number of mutations, including some in the spike protein region. Just like B.1.1.7, there are concerns this strain may be more transmissible and may also be potentially resistant to existing COVID-19 vaccines.
That said, just like the other variant strains, there is not enough information to confirm if these concerns are true.The potential increased transmissibility of the new strains may affect the ability of regions to reach herd immunity.
Herd immunity is usually calculated by reaching a threshold defined by the equation: 1-1/R-naught. For most infectious diseases, herd immunity is usually achieved when a majority of the population is immune through vaccination.
Let’s look at the herd immunity equation and use measles as an example. Measles has an R-naught value of about 15.
So, one minus one over fifteen equals 0.93, meaning 93% of the population must be vaccinated to achieve herd immunity from the measles.
For COVID-19, the WHO estimates the R-naught value is between 2 and 4, so if we choose a middle value of 3, then, one minus one over 3 equals 0.66, meaning that 66% of the population must be vaccinated to achieve herd immunity from COVID-19.But the fact is that a herd immunity threshold for COVID-19 is fairly challenging to calculate because the disease is still relatively new, and COVID-19 data is currently volatile.
For example, early on in the outbreak it was hard to track down true positive cases because COVID-19 testing was unreliable.
Another issue relates to the wide variances of R-naught values between geographical locations. Populations with high adherence to COVID-19 precautions such as consistent mask wearing, social distancing, and implementation of stay at home orders have lower COVID-19 R-naught values than populations who do not adhere to these precautions.
We calculate these R-naught values by regularly running epidemiological studies in populations, where researchers track how the disease is moving through the given population.Looking at our herd immunity calculation again, if one region had an R-naught value of 3.5, the equation would be one minus one over 3.5, meaning that region would need to vaccinate 70% of its population to achieve herd immunity.If another region had an R-naught value of 10, then the equation would be one minus one over 10, meaning that region would need to vaccinate 90% of its population to achieve herd immunity.
But there’s a complication. Many people travel between regions frequently, which makes the true herd immunity number hard to calculate.
R-naught values within a region also change over time. As more people are vaccinated, transmission of the disease drops, which drops the R-naught value.
There have been cases of people being reinfected by the disease. Other factors that complicate calculating the herd immunity number even more is the demographics of a population, and which groups of people are being prioritized to receive vaccination.
So as the variant strains become more prevalent in the United States, more people will need to be vaccinated to achieve herd immunity.
Achieving herd immunity may become a challenge not only due to the new variant strains, but also due to the large number of people in the United States that are hesitant to receive the COVID-19 vaccines, which is estimated to be about 43% of the population.As a quick recap, we currently know there are at least three new strains of COVID-19 which were all first identified in 2020 in the United Kingdom, South Africa, and Japan, and the UK strain can spread the fastest between people.
Calculating a percentage of the population which needs to be vaccinated to achieve herd immunity is complicated by a number of factors including the different vaccines produced, population demographics, and compliance to COVID-19 precautions.
If the new strains are all more easily spread then more people in the population will need to be vaccinated to achieve herd immunity.
population demographics and compliance to covid-19 precautions. If the new strains are all more easily spread than more people in the population will need to be vaccinated to achieve
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