Can you test positive for covid-19 without being infectious? Covid-19 testing in the time of omicron: Everything you need to know Peak Infectiousness Of Covid-19 With Omicron is 3-6 Days After Symptom Onset, Says New Study

 

Covid-19 testing in the time of omicron: Everything you need to know

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

Health 10 January 2022

By Clare Wilson

Lateral flow tests may be less likely to detect the omicron variant

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.”

Article amended on 12 January 2022

We removed incorrect information about isolation rules in the US.

More on these topics:

How to recognize Covid-19 symptoms from the omicron variant

The list of symptoms of Covid-19 has grown longer and stranger throughout the pandemic. With so many people now vaccinated, the warning signs of an infection have grown more subtle and vague. That’s becoming especially evident as the omicron variant gallops around the world, squeezing through the nooks and crannies in the wall of immunity that’s been built over the past two years.

An international team of researchers has been tracking signs of infection throughout the pandemic with the Covid Symptom Study using a mobile app where users could self-report their symptoms. Data on the omicron variant is still preliminary, but a group of 171 app users in the United Kingdom, most of whom are vaccinated, recently reported that their top symptoms for omicron were a runny nose, headache, fatigue, sneezing, and a sore throat. These were also the top symptoms for people infected with the delta variant.

That’s a departure from “the classic three” Covid-19 symptoms of fever, cough, and loss of sense of smell or taste associated with earlier variants, researchers say.

“For most people, an omicron positive case will feel much more like the common cold, starting with a sore throat, runny nose, and a headache,” Tim Spector, a professor of epidemiology at King’s College London and the lead scientist for the symptom study, told the BBC this week. “We need to change public messaging urgently to save lives.”

Among the 171 people in the recent symptom data analysis who were suspected or confirmed to be infected with omicron by Britain’s National Health Service, the symptom study team found only half reported fever, cough, or a loss of taste or smell.

Researchers in Norway recently reported similar findings from an omicron outbreak among fully vaccinated guests of a Christmas party. In 87 confirmed or probable cases, the most common symptoms were cough, runny or stuffy nose, fatigue, sore throat, and headache. Just over half reported a fever, while 23 percent experienced a loss of taste and 12 had a decline in smell.

These cases are further evidence that the omicron variant is the most transmissible version of the virus so far, and it seems to be better able to evade prior immunity. Vaccines in the US still offer strong protection against severe illness, however, especially with a booster shot.

“We know we will continue to hear more about people who get infected who are vaccinated,” CDC Director Rochelle Walensky said at a White House press conference this week. “These people may get mild or asymptomatic infections and could unknowingly spread those infections to others.”

In South Africa, one of the first places where the omicron variant was detected, widespread vaccinations against the disease combined with some immunity from prior infection may explain why omicron seems to present with milder symptoms.

“We believe that it might not necessarily just be that omicron is less virulent, but we believe that this coverage of vaccination, also in addition to natural immunity of people who have already had contact with the virus, is also adding to the protection,” South Africa’s Health Minister Joe Phaahla told reporters last week. “That’s why we are seeing mild illness.”

In the US, 73 percent of the population has had at least one dose of a Covid-19 vaccine and more than 50 million people have been infected previously, so a significant portion of the population has some degree of protection against the disease.

Even so, some people with omicron will fall severely ill. According to the Centers for Disease Control and Prevention, the Covid-19 symptoms that demand emergency medical care include sudden confusion; inability to stay awake; persistent chest pain or pressure; trouble breathing; and lips, fingernail beds, and skin turning blue, pale, or gray.

While a smaller percentage of the infected get sick enough to go to the hospital, the overall increase in cases from omicron could result in enough illness to overwhelm the US health care system in the coming months.

In addition, severe illnesses often start out with mild symptoms, and many Covid-19 treatments are most effective in the early stages of the disease. The Food and Drug Administration recently granted emergency authorization to the drug Paxlovid from Pfizer, the first oral antiviral to get a green light from the agency. It’s recommended for “mild-to-moderate” Covid-19 cases in people with risk factors for severe disease.

The emergence of the cold-like symptoms with the omicron variant means that getting tested to confirm whether someone is infected with Covid-19 is more critical than ever to slow the spread of the virus. For people with preexisting health conditions, identifying infections early is key to deploying effective treatments in time.

Frequent rapid testing for Covid-19 can catch omicron cases, though they tend to have lower accuracy compared to more expensive and time-consuming PCR tests. Many local health departments are scaling up their public testing systems, and the FDA has increased the number of rapid rests authorized for use. But in some areas, rapid tests remain scarce and too costly to use regularly.

So it’s crucial to take mild Covid-19 symptoms seriously and just as important to prevent infections in the first place. That requires getting vaccinated against Covid-19, getting a booster dose if eligible, wearing an effective face mask in public settings, and social distancing. Despite the latest twists in the pandemic, these measures remain the best bets for keeping the virus in check

Peak Infectiousness Of Covid-19 With Omicron is 3-6 Days After Symptom Onset, Says New Study

A new Japanese study has shown that people have peak viral loads 3-6 days after the onset of ... [+] symptoms, raising further doubt about the CDC's decision to lower self-isolation time from 10 to 5 days.

getty

A new study conducted by Japanese researchers has shown that peak viral loads in people infected with omicron occur between 3 to 6 days after the onset of symptoms. The study raises further concerns about the CDC cutting the self-isolating time for people with Covid-19 to 5 days, not 10.

The report was published online on January 5th by the Japanese Institute of Infectious Diseases and looked at 21 people with Covid-19 caused by the omicron variant. 19 of the people in the study were vaccinated and 2 were unvaccinated. 4 people were asymptomatic and 17 experienced mild symptoms.

Graphs show the amount of SARS-CoV2 virus (omicron variant) as quantified by real-time PCR after ... [+] diagnosis and symptom onset.

Japanese National Institute of Infectious Diseases Disease Control and Prevention Center, National Center for Global Health and Medicine

The researchers took 83 respiratory samples from the 21 people and measured the amount of SARS-CoV2 virus present using a technique called real-time PCR, finding that levels were highest between 3-6 days since diagnosis and post symptom onset. Strikingly, levels remained high in almost all patients between 7-9 days, with some patients having significant levels of virus genetic material detectable even two weeks after their original diagnosis.

Using real-time PCR to detect virus is unable to conclude whether the viral genetic material detected actually comes from virus which is able to infect people, or dead or dying virus. But the Japanese researchers also did experiments to culture live virus from the samples, finding the results to be similar to the real-time PCR studies.

However, ten days post diagnosis, the researchers were unable to culture any live virus from any of the samples, strongly indicating that none of the study participants would be infectious at that stage, even if the genetic material was detectable.

The news will likely add to growing concern, after the CDC cut recommended isolation time from 10 days to 5 days on December 27th. On Friday, CDC Director Rochelle Walensky spoke to Today, saying: “We are now standing on the shoulders of years of science that has demonstrated that if you are infected, you are most contagious in the one to two days prior to your symptoms and the two to three days after your symptoms. So we know that the vast majority of your contagiousness by day five is really behind you.”

Despite low numbers of patients involved, the Japanese study would appear to contradict Walensky’s assurances. Since the announcement, concerned people have been sharing their rapid antigen test results on social media, many of them testing positive and remaining symptomatic well past the 5 days they would be required to self-isolate by the CDC.

With numerous previous SARS-CoV2 coronavirus variants, several studies have shown that in most people, a peak of infectiousness occurs before, or shortly after symptom onset. But it looks like omicron may be different and some experts have suggested that an urgent re-think of the CDC guidelines are needed, as well as recommending a negative test as a requirement to end isolation.

The American Medical Association was the latest in a long line of organizations to oppose the move to shorten the self-isolation time after Covid-19 infection and it remains to be seen whether the CDC changes or reverses its stance as the U.S. sets daily world records of reported cases, with the number of people in hospital and ICU’s quickly rising.

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