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New research suggests that new coronavirus variants may spread more easily than the regular, or wild type coronavirus.
Fifty-five countries have now reported the presence of the coronavirus variant B.1.1.7, originally identified in the UK, and 23 countries have identified the 501Y.V2 variant, originally identified in South Africa.
It’s important to note that most of the research characterising the new variants has been published as “preprints”, which means that the studies have not yet gone through the usual peer review and journal publication process.
Mutations in the variants change the structure of the “spike” proteins, which is the mechanism by which the coronavirus attaches to cells.
Two separate studies have looked at the “transmissibility” of the B.1.1.7 variant, that is how easily it spreads. One paper from researchers at the Centre for Mathematical Modelling of Infectious Diseases (CMMID) in the UK, used modelling to explore different explanations for the surge in prevalence of the B.1.1.7 variant. They found “strong evidence of higher relative transmissibility estimated at 56% higher than preexisting variants”.
They also acknowledge that there are other mechanisms that might produce similar outcomes, such as an increase in the duration for which the virus is infectious.
Another study, with researchers collaborating from several institutions, estimated transmissibility for B.1.1.7 in the UK to be approximately 47% higher than other coronavirus types.
So what does this mean?
One the most important characteristics of viruses and other pathogens is how contagious or transmissible they are. One key measure is the R0, or basic reproduction number, which indicates how many new cases one infected person generates.
So for an R0 of three we would expect each new case of a disease to produce three other infections. This is not just a measure of the inherent infectiousness of a disease. It also depends on other factors, including the rate of contact within a population and the duration of the infectious period. It’s a situation-dependent value, so in one city the R0 might be higher and in another lower. It also assumes that the entire population is susceptible to the disease.
Earlier in the pandemic, with fewer interventions like social distancing and masks, the mean for various estimates of R0 for the coronavirus was around 2.6. Given a 50% increase in transmissibility, the R0 for a more infectious variant in the same situation might be around 3.9:
But the R0 is not the only important number. The effective reproduction number, R, is a value that takes into account the susceptibility of the population. With any R value greater than 1 the infection will increase, spreading through the population.
But if some people are not susceptible to infection – because of immunity through vaccination, because they have previously been infected or because of other biological reasons – or if transmission is curbed due to part of the population being isolated, or through the use of masks, then the effective R value declines.
If the effective R is reduced below one the spread can be halted.
So, for example, one of the papers published on B.1.1.7 found that the effective R for wild type coronavirus was around 0.85 during lockdowns in various parts of the UK. This means that with these interventions, new cases were decreasing. Here you can see how an effective R of 0.85 results in cases trending to zero:
However, at the same time the B.1.1.7 variant had an effective R of around 1.25. In the same chart you can see how an effective R of 1.25 results in cases increasing, despite the lockdown conditions still being effective against the wild type.
However, when lockdown and other interventions are tightened, the effective R can be reduced below 1 even for the more infectious variant, lowering new case numbers.
This all means that in areas where more infectious variants are established in the community current controls are likely to be less effective and need to be strengthened to prevent the risk of an increase in cases, deaths and long-term illness.
In countries such as Australia, Vietnam or New Zealand, where potentially more infectious variants have been found only in quarantined travellers, existing controls may be sufficient unless it is transmitted into the community, according to Hassan Vally, associate professor in epidemiology at La Trobe University, Australia.
“We just don’t want this virus to get established, because if it does get established it can spread throughout the population quicker, and be harder to control,” he said.
“But if you’re coming from a low base, then you should be able to cope with it using much the same strategies as we are using now.”
However, in countries such as the UK and the US, the situation is more concerning.
“The change from a virus circulating to having a higher R value, because of the multiplicative effect, and exponential growth, you’re going to see the threat to the population be much greater,” Vally said.
Stuart Turville, an associate professor in virology and immunology at the Kirby Institute, said the findings of the preprint studies would need to be verified by further work, but any increase in transmissibility from a coronavirus variant would “raise the bar” for controls.
“If this thing becomes fitter, you raise the bar for antibodies, you raise the bar for quarantine, you raise the bar for lockdowns, it becomes a harder target,” he said.
Turville said the most important question with emerging coronavirus variants is the effect any mutations will have on the vaccine response.
Early research, again published as preprint studies, does suggest that vaccines are effective against the B.1.1.7 variant, but there may be complications from the 501Y.V2 variant.
Source: The Guardian
Keyword: New coronavirus variants may spread more easily, so what does this mean for the fight against Covid? | News