UK variant, Ro and herd immunity

The new SARS-CoV-2 variant first appearing in southern England has a transmission advantage of 0.4 to 0.7 points higher in reproduction number, also known as R0, compared to the initial strain, British researchers found.

From the study itself:

There is a consensus among all analyses that the VOC has a substantial
transmission advantage, with the estimated difference in reproduction numbers between VOC and non-VOC ranging between 0.4 and 0.7, and the ratio of reproduction numbers varying between 1.4 and 1.8.

The researchers published their findings on the school’s website. VOC means “variant of concern”.

In other words, this new variant has an Ro which is 1.4 to 1.8 times higher than the previously circulating predominant strain.

CDC has concluded that based on genetic studies (discussed in a previous post) and reactivity to antibodies found in the blood of vaccinated individuals it appears unlikely to impact COVID-19 vaccine effectiveness. This conclusion has been reached by multiple immunologists who did those studies. (See https://practical-evolutionary-health.com/2020/12/31/new-uk-sars-cov-2-variant-we-see-no-evidence-that-the-reported-mutations-would-substantially-increase-reinfection-risk-or-decrease-vaccine-efficacy/)

So what is the reproduction number? Ro is the average number of individuals infected by one person. A Ro of 2 means that every infected person on average infects 2 other people.

When a critical proportion of a population becomes immune, called the herd immunity threshold (HIT), the disease no longer spreads exponentially in the population. The disease reaches an endemic steady state. It neither grows nor declines exponentially.

From Wikipedia:

This threshold can be calculated from the effective reproduction number Re, which is obtained by taking the product of the basic reproduction numberR0, the average number of new infections caused by each case in an entirely susceptible population that is homogeneous, or well-mixed, meaning each individual can come into contact with every other susceptible individual in the population,[and S, the proportion of the population who are susceptible to infection, and setting this product to be equal to 1:

Ro X S = 1

S can be rewritten as (1 − p), where p is the proportion of the population that is immune so that p + S equals one. Then, the equation can be rearranged to place p by itself as follows:

Ro x (1-p) = 1, 1-p = 1/Ro, so {\displaystyle p_{c}=1-{\frac {1}{R_{0}}}.}

When the effective reproduction number Re of a contagious disease is reduced to and sustained below 1 new individual per infection, the number of cases occurring in the population gradually decreases until the disease has been eliminated.

An assumption in these calculations is that populations are homogeneous, or well-mixed, meaning that every individual comes into contact with every other individual, when in reality populations are better described as social networks as individuals tend to cluster together, remaining in relatively close contact with a limited number of other individuals. In these networks, transmission only occurs between those who are geographically or physically close to one another. The shape and size of a network is likely to alter a disease’s HIT, making incidence either more or less common

But transmission is not just affected by the characteristics of the virus, it is also affected by the behavior of the population in which the virus is observed. So it is complicated. As stated by the authors of the transmission study.

We note that these estimates of transmission advantage apply to a period
where high levels of social distancing were in place in England; extrapolation to other
transmission contexts therefore requires caution.

So if social distancing is relaxed, fewer people wear masks, more people congregate, then this variant could have a much higher Ro.

Ro for measles is 12-18 rendering HIT at 92-95%

Ro for SARS CoV-1 (2002-2004 pandemic) was estimated at 2-5 rendering HIT 50-80%

Ro for SARS CoV-2 (COVID-19) has been estimated at 2.5-4 giving and HIT of 60-75%.

This is not the first variant to demonstrate increased transmission. A new variant emerged in February of 2020 called D614G which had a higher Ro compared to the previously circulating predominant strain. Such strains with higher transmission rates eventually become the predominant strain circulating in a population.

So just as more people suffer from pandemic fatigue and drop their guard we have a more easily transmitted virus. Now is not the time to loosen up on precautions.

In the context of the COVID 19 pandemic I will close with the usual summary.

  1. Avoid alcohol consumption (alcohol wreaks havoc with your immunity)
  2. Get plenty of sleep (without adequate sleep your immune system does not work well )
  3. Follow good sleep habits
  4. Exercise, especially out of doors in a green space, supports the immune system
  5. Get some sunshine and make sure you have adequate Vitamin D levels.
  6. Eat an anti-inflammatory diet rich in micronutrients.
  7. Practice stress reduction like meditation and yoga which improves the immune system
  8. Eliminate sugar-added foods and beverages from your diet. These increase inflammation, cause metabolic dysfunction, and suppress immunity.
  9. Eliminate refined-inflammatory “vegetable oils” from your diet, instead eat healthy fat.
  10. Clean up your home environment and minimize your family’s exposure to environmental toxins by following recommendations at EWG.org with regards to household products, personal care products, and organic foods. (https://www.ewg.org/)

THIS WEBSITE PROVIDES INFORMATION FOR EDUCATIONAL PURPOSES ONLY. CONSULT YOUR HEALTH CARE PROVIDER FOR MEDICAL ADVICE.

Eat clean, drink filtered water, love, laugh, exercise outdoors in a greenspace, get some morning sunlight, block the blue light before bed, engage in meaningful work, find a sense of purpose, spend time with those you love, AND sleep well tonight.

Doctor Bob

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