Friday, October 29, 2021

‘Immunity wanes’: Study finds vaccinated people easily transmit Delta in households

London: The Delta coronavirus variant can transmit easily from vaccinated people to their household contacts, according to a British study, although contacts were less likely to get infected if they were vaccinated themselves.

The Imperial College London study illustrates how the highly transmissible Delta variant can spread even in a vaccinated population.

The researchers underlined that this did not weaken the argument for vaccination as the best way of reducing serious illness from COVID-19 and said booster shots were required.

They found infections in the vaccinated cleared more quickly, but the peak viral load remained similar to the unvaccinated.

“By carrying out repeated and frequent sampling from contacts of COVID-19 cases, we found that vaccinated people can contract and pass on infection within households, including to vaccinated household members,” Dr Anika Singanayagam, co-lead author of the study, said.

“Our findings provide important insights into... why the Delta variant is continuing to cause high COVID-19 case numbers around the world, even in countries with high vaccination rates.”

The study, which enrolled 621 participants, found that of 205 household contacts of people with Delta COVID-19 infection, 38 per cent of household contacts who were unvaccinated went on to test positive, compared to 25 per cent of vaccinated contacts.

Vaccinated contacts who tested positive for COVID-19 on average had received their shots longer ago than those who tested negative, which the authors said was evidence of waning immunity and supported the need for booster shots.

Imperial epidemiologist Neil Ferguson said that the transmissibility of Delta meant that it was unlikely Britain would reach “herd immunity” for long.

“That may happen in the next few weeks: if the epidemic’s current transmission peaks and then starts declining, we have by definition in some sense reached herd immunity, but it is not going to be a permanent thing,” he told reporters.

“Immunity wanes over time, it is imperfect, so you still get transmission happening, and that is why the booster programme is so important.”


How much less likely are you to spread covid-19 if you're vaccinated?

People who are fully vaccinated against covid-19 are far less likely to infect others, despite the arrival of the delta variant, several studies show. The findings refute the idea, which has become common in some circles, that vaccines no longer do much to prevent the spread of the coronavirus.

“They absolutely do reduce transmission,” says Christopher Byron Brooke at the University of Illinois at Urbana-Champaign. “Vaccinated people do transmit the virus in some cases, but the data are super crystal-clear that the risk of transmission for a vaccinated individual is much, much lower than for an unvaccinated individual.”

A recent study found that vaccinated people infected with the delta variant are 63 per cent less likely to infect people who are unvaccinated.

This is only slightly lower than with the alpha variant, says Brechje de Gier at the National Institute for Public Health and the Environment in the Netherlands, who led the study. Her team had previously found that vaccinated people infected with alpha were 73 per cent less likely to infect unvaccinated people.

What is important to realise, de Gier says, is that the full effect of vaccines on reducing transmission is even higher than 63 per cent, because most vaccinated people don’t become infected in the first place.

De Gier and her team used data from the Netherlands’ contact tracing system to work out the so-called secondary attack rate – the proportion of contacts infected by positive cases. They then worked out how much this was reduced by vaccination, adjusting for factors such as age.

De Gier says they cannot calculate the full reduction in transmission due to vaccination, because they don’t know exactly how much vaccination reduces the risk of infection. But even assuming vaccination only halves the risk of infection, this would still imply that vaccines reduce transmission by more than 80 per cent overall.

Others have worked out the full effect. Earlier this year, Ottavia Prunas at Yale University applied two different models to data from Israel, where the Pfizer vaccine was used. Her team’s conclusion was that the overall vaccine effectiveness against transmission was 89 per cent.

However, the data used only went up to 24 March, before delta became dominant. The team is now using more recent data to work out the impact of delta, says Prunas.

The idea that vaccines are no longer that effective against transmission may derive from news reports in July claiming that vaccinated people who become infected “can carry as much virus as others”. Even if this were true, however, vaccines would still greatly reduce transmission by reducing infections in the first place.

In fact, the study that sparked the news reports didn’t measure the number of viruses in someone directly but relied on so-called Ct scores, a measure of viral RNA. However, this RNA can derive from viruses destroyed by the immune system. “You can measure the RNA but it’s rendered useless,” says Timothy Peto at the University of Oxford.

Read more: How mRNA is transforming the way we treat illnesses from flu to cancer
There are now several lines of evidence that Ct scores aren’t a good measure of the amount of virus someone has. Firstly, the fact that infected vaccinated people are much less likely to infect others. Peto has done a similar study to de Gier using contact tracing data from England and gotten similar results.

Secondly, Peto’s team specifically showed that there is little connection between Ct scores and infectiousness. “It appeared people who were positive after vaccination had the same viral load as the unvaccinated. We thought they were just as infectious. But it turns out you are less infectious,” says Peto. “That’s quite important. People were over-pessimistic.”

Yet another line of evidence comes from a study by Brooke. His team took samples from 23 people every day after they first tested positive until the infection cleared and performed tests, including trying to infect cells in a dish with the samples.

With five out of the six fully vaccinated people, none of the samples were infectious, unlike most from unvaccinated people. The study shows that vaccinated people shed fewer viruses and also stop shedding sooner than unvaccinated people, says Brooke.

The one bit of bad news is that Peto’s study shows that the protection a vaccine provides against an infected person infecting others does wane over time, by around a quarter over the three months after a second vaccine dose. “This has made me a believer in boosters,” he says. “They ought to get on with it, given that we are in the middle of a major outbreak [in the UK].”


China problems: Europe and US face magnesium supply crisis

China's state-run tabloid Global Times says it is "unrealistic" for China to meet the urgent demand for magnesium from Europe, where stocks of the raw material could run out next month.

The paper said the magnesium shortage was not a simple issue that could be resolved by increasing production from China. "Global supply chains face challenges of climate change targets, high inflation and logistics obstacles," it noted in an editorial on Monday.

"China's efforts to tackle these challenges at its own pace are responsible and should be respected.

"It is essential to establish an economic and trade consultation mechanism on the supply chain between China and the EU [European Union]."

The European market is almost entirely (95 per cent) dependent on China for the supply of magnesium, a key ingredient in aluminium, which is used to make cars and in building supplies, among other things. Magnesium is also used in iron and steel producing.

Last Friday, a dozen industry groups issued a joint statement to urge European leaders to work towards immediate actions with their Chinese counterparts to mitigate the critical shortage issue.

"Supply of magnesium originating from China has either been halted or reduced drastically since September 2021, resulting in an international supply crisis of unprecedented magnitude," they said.

"This issue, if not resolved, threatens thousands of businesses across Europe, their entire supply chains and the millions of jobs that rely on them."

The remaining magnesium stocks in Europe were trading at $US10,000-$US14,000 a tonne, up from around $US2,000 per tonne earlier this year, the industry groups said.

The European Commission has reportedly been holding talks with China to resolve the shortage.

"Europe has none of its own supply and relies on China for imports," analysts at investment bank Morgan Stanley noted.

"With limited vessel availability and shipping times of at least two months, Europe could see limited supply until May."

Although the US is less reliant on China for magnesium, its aluminium producers are facing a similar supply issue. The largest US aluminium billet maker, Matalco, has warned of an upcoming output reduction, while the largest US raw aluminium producer, Alcoa, has expressed concerns about magnesium scarcity, Bloomberg reported.

China produces around 87 per cent of the world's magnesium, but that has been affected by the country's recent power crisis.

The Chinese government has been trying to curb domestic power consumption and regulate soaring electricity prices. Many magnesium plants have been either shut down or halved their production capacities due to the power cuts. Chinese state media has reported that China's magnesium exports are likely to drop 10 per cent this year.

"Magnesium production is the latest victim of China's power crunch as well as the government's increasingly hardline approach to emission reduction," Peter Cai, a China analyst from the Lowy Institute, told the ABC.

"Authorities are shutting down [power] plants to meet their emission reduction target."

China is still one of the world's largest carbon emitters, but President Xi Jinping is aiming for the country's CO2 emissions to peak before 2030 and to achieve carbon neutrality before 2060.

A magnesium shortage could have widespread impacts across autos, aerospace, iron or steel, chemicals, beer and soft drinks, and consumer goods.

Morgan Stanley analysts noted that many lightweight alloys relied on magnesium. "Magnesium's light weight and strengthening properties make it essential for aluminium alloys (eg sheet used in autos, beverage cans)," they wrote.

"It is also used for die-casting auto parts, as a desulphurising agent in steel, to make ductile iron, in chemicals and more."

While the analysts noted that there had been some production recovery in October, utilisation was capped at 40 per cent of capacity and that still created a big challenge for the global market.

Car-makers are set to be particularly hard hit, as they still struggle with shortages of computer chips.

"Depressed auto production levels have been masking the extent of the impact of the existing shortages; it may not be possible for auto production to recover as forecasters such as IHS anticipate."




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