Sunday, January 16, 2022
Covid-19 testing in the time of omicron
With omicron infections surging around the world, many countries are changing their coronavirus testing guidelines to better deal with the new variant and the huge number of cases it is causing. Here's what you need to know
Can you test positive for covid-19 without being infectious?
Even if you have had three doses of coronavirus vaccine, a positive lateral flow test (LFT) result means you are infectious to other people because virus protein is present in large quantities in your nose or throat. For that, the virus must be actively multiplying inside your cells.
However, PCR tests continue to give positive results for days to weeks after an infection, because they can detect tiny quantities of the virus’s genetic material, which aren’t necessarily infectious.
How have testing rules changed?
Many countries have lessened their restrictions for people with covid-19 since the start of the surge caused by the omicron variant. In the UK, the isolation period for infected people has been cut from 10 days to seven – as long as you get a negative result on two LFTs, also known as rapid antigen tests. These must be done on days six and seven, and carried out at least 24 hours apart. People should remain cautious around others and avoid those who are vulnerable, though.
Could the isolation period be shortened further?
In the US, the isolation period has been cut to five days for people who have no symptoms or whose symptoms are on the wane, although you should still wear a mask around other people for a further five days. The UK Health Security Agency (UKHSA) says it has no plans to follow suit.
Why do some people still test positive on day seven even though they feel well?
Symptoms may not reflect how much virus is present in a person’s throat or nose – they could have replicating virus but no symptoms and vice versa. “There’s huge variation in the length of infection, and huge variations in viral load,” says Al Edwards at the University of Reading, UK.
The UKHSA estimates that between 10 and 30 per cent of people will still be positive at day six – and that 5 per cent of people will still be positive at day 10, although the guidance says you no longer have to isolate on day 11, no matter what your LFT results show.
How about confirmatory PCR tests?
In the UK, people who test positive by LFT will no longer need to take a follow-up PCR test, a temporary change coming into effect on 11 January. This is because background levels of covid-19 are so high – with about 1 in 15 people infected in the last week of December – that a positive LFT result is currently less likely to be false.
Does this mean we can just rely on LFTs now?
No. Anyone in the UK with covid-19 symptoms but a negative LFT result must still take a PCR test to rule out an infection, because LFTs have too high a rate of false negatives – telling someone they are covid-19 free when they really are infected – to rely on them if you have symptoms. There are several reasons why LFTs are prone to false negatives, including people failing to swab their nose or throat properly and failing to mix the swab well with the testing fluid, says Edwards. “LFTs are only able to detect large amounts of virus.”
Are false negatives more likely with omicron?
Opinions differ. The UKHSA says initial investigations suggest that LFTs are as sensitive to omicron as they are to the delta variant that was predominant in most countries until December, although it is continuing further tests. But the US Food and Drug Administration has said LFTs may be less sensitive at detecting omicron.
It is possible that LFTs that only involve swabbing the nose may be more likely to give false negative results for omicron, because some studies have suggested that this variant is more likely to reach high levels in saliva before it does in nasal mucus. One very small US study put online last week suggests that in omicron infections, virus levels peaked in saliva one or two days before they did in nasal mucus, although this analysis included only five people.
“Omicron might be exacerbating that differential, where you have your throat and your salivary specimens turning positive earlier,” says Michael Mina at US testing company eMed. A study from South Africa also found that saliva swabs were generally more sensitive than nasal swabs for omicron, whereas it is the opposite pattern for the delta variant.
Should we switch to using throat swabs over nasal swabs?
Opinions differ there too. In the UK, LFTs made by Innova instruct users to take throat and nasal swabs, while others only use nasal swabs. In the US, only nasal LFTs are available, so people are less used to taking throat swabs. “If at all possible, put your swab in both your throat and nasal cavities,” Deenan Pillay at University College London said at last week’s meeting of Independent SAGE, an independent group of scientists in the UK. “If the swabs are shorter, stick your fingers in more to get to the back of the throat.”
But Edwards says people should only use tests exactly as instructed. “If you change the way you use a test, it doesn’t meet the manufacturer’s requirements. [Lower levels in the nose] are probably not going to make that much difference to how accurate the tests are. Most people will be either not infected or will have tons of virus. We should stick to doing tests the proper way.”
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Repeat COVID-19 Vaccine Booster Shots Trigger Regulator Warning About Immune-System Risks
The EU’s drug regulator has expressed doubts about whether a second booster dose of the currently available COVID-19 vaccines would be a sustainable long-term approach.
“There is an emergency discussion around the possibility of giving a second booster dose with the same vaccine currently in use. Data has not yet been generated to support this approach,” Marco Cavaleri, the European Medicines Agency’s (EMA) head of vaccines strategy, told a media briefing.
He added later, “We would like to see this data before we can make any recommendation, but at the same time we are rather concerned about a strategy that [involves] repeated vaccinations within a short term.”
An additional vaccine booster shot “could be considered as part of a contingency plan,” but “repeated vaccinations within short intervals will not represent a sustainable long term strategy,” according to Cavaleri.
Concerns Over Immune Response
When asked to expand on his statements, Cavaleri said that for a hypothetical approach of giving vaccine booster shots frequently, such as every four months, “we will end up potentially having problems with immune response and immune response may end up not being as good as we would like it to be, so we should be careful in not overloading the immune system with repeated immunization.”
He also noted that continuous administration of boosters can also lead to fatigue in the population.
“It will be much better to start thinking about an administration of boosters that is more spaced in time,” Cavaleri said.
The EMA is in conversation with vaccine developers in case there’s a need to update the current vaccines, according to Cavaleri. But he said any change “would have to be coordinated globally.”
More data on the effect of the Omicron coronavirus variant on vaccines and a better understanding of the evolution of the current wave are needed to decide whether an Omicron-specific vaccine was needed.
“While a monovalent Omicron vaccine would represent an obvious candidate to be investigated, other options such as a multivalent vaccine cannot be ruled out as potential alternatives,” Cavaleri said.
A Strategy to ‘Anticipate the Next Move’
“It is important that there is a good discussion around the choice of the composition of the vaccine to make sure that we have a strategy that is not just reactive after the virus changes, but try to anticipate what could be the next move and try to come up with an approach that will be suitable in order to prevent a future variant that, in any case, will emerge,” Cavaleri said.
The EMA has called for a meeting with global regulators on Jan. 12, which will include officials from the U.S. Food and Drug Administration.
“Tomorrow we will be looking at all the evidence that we have so far with the current vaccine, so the extent by which they are still providing vaccine effectiveness and whether indeed we should still think that giving a booster shot at this point in time is the best strategy,” Cavaleri said.
He noted that the World Health Organization “will play a critical role” in decision-making.
Cavaleri noted that the CCP (Chinese Communist Party) virus, which causes COVID-19, “is still behaving as a pandemic virus, and the Omicron emergency is currently showing that.”
“So we should not forget we are still in a pandemic,” he said. “Nevertheless, with increase of immunity in the population and with Omicron there will be a lot of natural immunity taking place on top of vaccination, we will be vastly moving toward a scenario that will be closer to endemicity.”
Separately, he noted, “Ideally, if you want to move toward a scenario of endemicity, then such boosters should be synchronized with the arrival of the cold seasons in each of the hemispheres, similarly to what we’re doing with influenza vaccines.”
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Anti-viral chewing gum?
University of Pennsylvania scientists used saliva samples of COVID-19 patients to test a chewing gum laced with a plant-grown protein.
The protein traps the SARS-CoV-2 virus to reduce viral load in saliva and potentially hamper transmission.
According to the team of researchers, the chewing gum contains the ACE2 protein to neutralize the virus.
EurekAlert! noted:
The work, led by Henry Daniell at Penn’s School of Dental Medicine and performed in collaboration with scientists at the Perelman School of Medicine and School of Veterinary Medicine, as well as at The Wistar Institute and Fraunhofer USA, could lead to a low-cost tool in the arsenal against the COVID-19 pandemic. Their study was published in the journal Molecular Therapy.
“SARS-CoV-2 replicates in the salivary glands, and we know that when someone who is infected sneezes, coughs, or speaks some of that virus can be expelled and reach others,” says Daniell. “This gum offers an opportunity to neutralize the virus in the saliva, giving us a simple way to possibly cut down on a source of disease transmission.”
Since the experimental COVID-19 injections don’t prevent transmission, Daniell’s work provides an innovative solution to potentially reduce viral load.
Recent research indicates vaccinated and unvaccinated individuals can carry similar viral loads.
EurekAlert! explained how the scientists tested the chewing gum:
To test the chewing gum, the team grew ACE2 in plants, paired with another compound that enables the protein to cross mucosal barriers and facilitates binding, and incorporated the resulting plant material into cinnamon-flavored gum tablets. Incubating samples obtained from nasopharyngeal swabs from COVID-positive patients with the gum, they showed that the ACE2 present could neutralize SARS-CoV-2 viruses.
Those initial investigations were followed by others at The Wistar Institute and Penn Vet, in which viruses, less-pathogenic than SARS-CoV-2, were modified to express the SARS-CoV-2 spike protein. The scientists observed that the gum largely prevented the viruses or viral particles from entering cells, either by blocking the ACE2 receptor on the cells or by binding directly to the spike protein.
Finally, the team exposed saliva samples from COVID-19 patients to the ACE2 gum and found that levels of viral RNA fell so dramatically to be almost undetectable.
After the positive findings, the researchers have sought permission to conduct a clinical trial with COVID-19 positive patients.
The research remains in the beginning stages, but clinical trials proving the gum is safe and effective can potentially be a game-changer to prevent transmission.
The peer-reviewed study was published in the journal Molecular Therapy.
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Also see my other blogs. Main ones below:
http://edwatch.blogspot.com (EDUCATION WATCH)
http://antigreen.blogspot.com (GREENIE WATCH)
http://pcwatch.blogspot.com (POLITICAL CORRECTNESS WATCH)
http://australian-politics.blogspot.com/ (AUSTRALIAN POLITICS)
http://snorphty.blogspot.com/ (TONGUE-TIED)
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