Variant Generation and Vaccine Efficacy

3 min readOct 10, 2021

Mu Variant

Columbia has detected Mu since January 2021 and has recently been the subject of various articles. Examining the data on variants in Columbia, it can be seen that Delta is actually outcompeting Mu, meaning that it is unlikely that Mu reaches global dominance. [1]

Variants detected in Columbia over time. Source: nextstrain.org

Variant Generation

It is a rather common fallacy to think that vaccination will drive the emergence of new and worse variants. Analogies are drawn between this situation and antibiotic resistance. There exist many differences mechanistically between the two situations, however the case of variant generation requires one thing: transmission.

Vaccines curb transmission and reducing viral load, meaning that they will not act as an evolutionary pressure. [2,3]

In simple terms, evolutionary pressure for variant selection requires a large number of viruses to be produced and from that large number selection will occur. Vaccines drastically reduce the number of viruses produced and so do not drive evolution in such a direction. [4]

Boosters

The FDA has authorised booster shots for people aged 65 and above and for people whose occupation exposes them to high risk of contracting SARS-CoV-2. [5]

Since the initial readouts of the clinical trials for the vaccines, many observational studies have been carried out (sources that use non-technical language often refer to this as “real-world data”; a slight misnomer that is partially adopted here).

These have reported both varying levels of vaccine efficacy (VE) and disagree whether and how much immunity is waning. There are many confounding variables in such studies, making it very hard to get accurate and precise readings on VE. [6]

In most contexts, VE is measured against symptomatic disease. It can be argued that VE against transmission or against hospitalisation are more important. Regardless, the best conducted studies so far have shown a very modest waning of VE for hospitalisation/severe disease. VE for symptomatic disease and transmission is much harder to assess outside of a randomised controlled trial setting. [7,8]

Antibody levels seems to drop over time, however this is expected and normal after vaccination. In addition, T-cells are also important when it comes to disease and their relationship to VE is unclear. [9]

The third shots definitely boost antibodies and will increase protection to some extent for some time. The exact extent is not known. [10]

An important and often overlooked point about the FDA booster approval is the excess doses the USA has on its hands. It is unfortunately not necessarily a case of third shots in the USA vs. first shots elsewhere in the world. For example, COVAX has secured 19 billion doses, but only ~300 million have been shipped around the world. [11]

Antibodies in the blood do not correlate with VE against infection, but with VE against severe disease, hospitalisation and death. A hypothesis has been put forward that VE for infection is controlled by antibodies in the mucous membranes, which current vaccines produce but most likely transiently. [12,13]

References

Variant Generation and Vaccine Efficacy

Written by Michael Bogdos