How much more contagious are the Covid-19 variants? The dangers of a more communicable disease, he explained.

A most contagious SARS-CoV-2 virus is the most deadly. Not because it makes any individual sicker, but because it affects more people. More illness means more cases: more mild cases, more severe cases, more long-term complications, more hospitalizations and more deaths.

There is no perfect estimate of how much more contagious the SARS-CoV-2 variant called B.1.1.7, which was first discovered in the UK, can be. There needs to be more careful laboratory work on animals to get it right, which can take a few more weeks. But preliminary estimates consider it to be among 30 percent and 70 percent more contagious. This variant is emerging all over the world: in the United States, Europe, Asia and elsewhere. It is especially worrying, considering that in the United States and elsewhere, the spread of the pandemic is still reaching new heights.

There is also a variant called 501Y.V2 that was found for the first time in South Africa; it seems less widespread than B.1.1.7, but it is also more contagious than the older variants. It is still possible that other more transmissible variants may emerge in the future. Scientists just don’t know.

Regardless of how transmissible any new variant is, any possible increase in transmissibility is extremely worrying for epidemiologists and other public health professionals. This means that now, more than ever, our collective and individual actions to prevent the spread are extremely important.

Here are some main reasons.

A more transmissible virus simply means more cases

The reason for concern about a more contagious variant of the virus is simple. “Once [the variant] become common, it will speed up transmission considerably, ”said Harvard epidemiologist Marc Lipsitch in a press call. Accelerated transmission means more boxes.

That’s because the virus grows exponentially. Any increase in its inherent transmissibility causes an increasing number of cases along the line, if control measures also do not accelerate to keep up.

With a 50% increase in infectiousness, “in less than two weeks, you have twice as many cases,” says Lipsitch. “And in a month or more, you have four, five times more cases. But this is very close. “It could be bigger, he says.

A more transmissible virus means that we need to work harder to stop the spread

Epidemiologists think of the transmissibility of a virus with a number called R, or the basic reproduction number. Describes how many new cases, on average, will follow a case of the virus.

At the beginning of the outbreak, before the world took action, epidemiologists estimated R to be about 2 or 3. Since then, thanks to our efforts (implemented inconsistently) – mask use, social distance, closing deals, etc – the R has been reduced in many states to about 1.1 to 1.2. But as long as the R value is greater than 1, the virus can spread exponentially.

Let’s say that a community has reduced its value from R to 1. Then, a 50% more transmissible variant appears. This may mean that the same mitigation effort that reduced the old virus variant to 1 now only reduces it to 1.5.

What it means: to fight a more transmissible version of the virus, communities need even tighter controls.

A virus 50 percent more transmissible, says Lipsitch, means “we need to reduce our contacts by a third more compared to the already tight restrictions [already in place] in order to return to the same place where we were. ”This could mean closing companies that have partially opened, closing schools and other blocking measures.

If communities do nothing in the face of a more contagious variant, the numbers can increase very quickly. Bill Hanage, another Harvard epidemiologist, led me through the following mental experiment.

Let’s say a community has the virus more or less under control. The R value in the area is 1, which means that the number of cases in the area remains constant, month by month.

In this scenario, “you have 1,000 cases now, and you will have 1,000 cases per month from now on,” says Hanage (his scenario assumes that it takes about five days for one infection to cause another). “Now let’s imagine that the virus is 50 percent more transmissible. …. 1,000 cases of this virus would now translate into more than 10,000 cases per month from now on, if you did nothing! “

Christina Animashaun / Vox

A more transmissible virus increases the number of people who need to be vaccinated

A more transmissible virus also raises the threshold for herd immunity, or the approximate estimate of the percentage of people in a population who need to obtain immunity, ideally through vaccination, in order for the outbreak to decrease in size.

The herd’s immunity limits depend on the value of R. The higher the value of R, the greater the limit. If a more transmissible variant becomes dominant around the world, pressure on vaccination campaigns will increase to vaccinate even more people. It appears that more than 70 percent of the population will need to be immune to achieve herd immunity (although the exact number needed is unknown). This is already an extremely high bar and difficult to overcome, given the slow early distribution of vaccines.

There is also the unrealized possibility that the virus may mutate into a form that reduces the effectiveness of current vaccines.

A more transmissible virus means more death

Good news about variant B.1.1.7: so far, it doesn’t seem to be more deadly than the older virus variants. In other words: any individual who receives it is no longer likely to end up in the hospital or die, according to the first data.

But more infections mean more deaths. “In general, the more people are infected, the number of hospitalizations and deaths increases in proportion to that number,” says Emma Hodcroft, molecular epidemiologist at the Swiss Institute of Preventive and Social Medicine. “So more cases are also bad news.”

A virus that is 50 percent more contagious is an even more deadly concern than one that is 50 percent more lethal, as an epidemiologist at the London School of Hygiene & Tropical Medicine Adam Kucharski explains on Twitter.

If a city has an R value of 1.1 and there are 10,000 people infected in a month, you would expect to see 129 deaths, he says.

Increase virus mortality by 50 percent in this scenario and you would expect 193 deaths – an increase of 49.6 percent.

Increase the contagiousness of the virus in this scenario by 50 percent and you will have 978 deaths, Kucharski found. This is an increase of 658%. It is a theoretical calculation, but the central point is the exponential effect, as Kucharski explains.

It is not entirely clear if this will happen

Again, the 50 percent increase in transmissibility estimate is just an estimate. And even if the new variants are more transmissible, it can be difficult to predict how much more transmissible they will be in different locations.

Hanage emphasizes that the 50 percent most communicable number reported is based on how this variant behaves in the UK. In a different place – with different adherences to social distance, different mitigation measures in place – the new variant could behave differently. It is complicated, yes, but this is an outbreak for you.

But even the hypothetical threat of a more communicable variant is a call to action.

To prevent further mutations from happening, to prevent more potentially problematic variants from appearing, we need to stop the spread of SARS-CoV-2 in general. On the one hand, it helps us to deal with the pandemic in general. But “it’s also conveniently how we get fewer emerging variants,” Angela Rasmussen, a virologist at the Georgetown Center for Global Health and Safety, told me in an interview in December. “If the virus is not replicating, it cannot mutate. And if it cannot mutate, new variants cannot emerge. “

The new variant means that our individual actions are more important than ever. This variant spreads in the same way as other variants of SARS-CoV-2, and the same precautions apply. Social distance, wearing a mask and ventilation are as important as ever.

With the new variant available, Lipsitch says: “Your isolation, quarantine and contact tracking are considerably more important, even more than before. So you are doing more for the world ”.