The Omicron variant of the virus that causes COVID19, SARS-CoV-2, is called BA.2 and now represents nearly 86% of all cases of COVID that have been genetically tested, according to the World Health Organisation.
The surge occurred as many countries lifted public health interventions but it is even more transmissible than its highly-contagious Omicron siblings, BA.1 and BA.1.1, though no more likely to cause severe disease, and scientists are divided over whether the return to normality is too fast.
Yet, although around half a million people in the UK tested positive in the past week or so, with the actual number of infections estimated to be more than four million, from today [Friday 1 April] the Government will no longer provide free universal testing.
Having recently experienced Omicron (yes, it is milder than the earlier variants but I found it much worse than ‘just a cold’), I am fascinated by two questions: should we continue to take any precautions and how and when should we test ourselves now that we have to pay for the test kits?
I talked to a scientist who has conducted studies of COVID19 outbreaks in forensic detail, and who fell ill with the disease in the first wave: Science Museum Group Trustee Prof Ajit Lalvani, who is Chair of Infectious Diseases, and Director of the National Institute for Health Research’s Health Protection Research Unit in Respiratory Infections, at Imperial College London. His answers are shown in italic.
WHEN I RECENTLY GOT OMICRON, MY LATERAL FLOW TEST, LFT, WAS ONLY POSITIVE THREE DAYS AFTER SYMPTOMS. IS THAT NORMAL?
Yes, false negatives are common. LFTs only produce a second red line (a positive result) above a certain threshold of virus. You can have a lot of virus, and your body knows it, and yet still be negative. In a recent study we published in the BMJ we found that LFTs would miss 20% of positive cases and you can infect a lot of people during this time.
SO, A LOT OF PEOPLE WHO THINK THEY MIGHT HAVE A COLD COULD BE INFECTING OTHERS WITH COVID FOR A FEW DAYS?
Yes, that is right. Symptoms are often caused by the immune response to the virus, and these responses may kick in faster if you’ve been vaccinated, or previously had COVID. So, the symptoms can be present and yet the LFT can show negative. So ideally, you should test daily from the onset of symptoms. If your initial results are negative they may well become positive after two or three days, when the amount of virus in the nose and throat reaches a peak. Alternatively, you can just test two to three days or so after the first symptoms.
WHAT SYMPTOMS SUGGEST IT IS COVID RATHER THAN A COMMON COLD?
The symptoms of COVID-19 vary. Those infected may not have any of the three main symptoms recognised on the government website, particularly if they have been vaccinated. As well as SARS-CoV-2, other respiratory viruses such as rhinovirus), influenza virus, and adenovirus can also cause cold and flu-like symptoms.
We found that the presence of two or more of the following symptoms are an early predictor of whether you have COVID19: muscle aches, headache, appetite loss and sore throat. But, again, these symptoms can develop, along with infectivity, before a LFT shows a positive. You can diagnose one or two days earlier this way.
WHY IS OMICRON MORE INFECTIOUS?
People infected with the Omicron variant of the coronavirus SARS-CoV-2 are almost 50% more likely to infect those they live with than are individuals infected with the Delta variant. One reason is the ability of Omicron to evade immunity generated by vaccines and that study showed that a third vaccine dose had a marginal beneficial effect on transmission of both Delta and Omicron compared to only two doses, although this protective effect was larger for the Delta variant than it was for Omicron.
The 54 mutations in Omicron’s genetic code — and particularly the 34 clustered in the code for a key protein called the spike on which the vaccines are based — weakens the ability of COVID-19 vaccines to prevent SARS-CoV-2 infection. However, it should be remembered that, though the vaccines offer limited protection against infection with Omicron, they are still effective at preventing severe disease.
WHAT SHOULD YOU DO IF VISITING A VULNERABLE PERSON?
You can be infectious without noticing symptoms, or before symptoms develop and, as I said, lateral flow tests may miss this. Doing a LFT immediately before visiting (e.g. same morning or same afternoon) helps to reduce the risk of passing infection to the vulnerable person, but by no means abolishes it.
The risk can be reduced further if: the visitor and the vulnerable person are vaccinated; the visitor limits unnecessary exposures in the five days prior to the visit; washes their hands immediately before visiting; wears a face-mask and maintains social distancing; and if the meeting is held outside or in a well-ventilated room (for example, with doors and/or windows open).
For vulnerable people, it is best to take a multi-layered approach to reducing risk – i.e. perform as many of these risk reducing strategies as possible, as set out by Independent SAGE
HOW LIKELY ARE YOU TO BE INFECTIOUS IF YOU HAVE ENCOUNTERED SOMEONE WITH COVID?
After contact with a confirmed COVID-19 case, there is a risk of contracting (and then transmitting) the infection for up to 10 days.
WHEN, AFTER INFECTION, IS IT SAFE TO RETURN TO WORK, SCHOOL OR TRAVEL?
After testing positive, two consecutive negative LFT results on days six and seven after symptom onset gives high confidence that you are no longer infectious. Often the LFTs continue to test positive even though the person is no longer infectious, but there is no better easily available test to determine the end of infectiousness. Most adults are no longer infectious 10 days after onset of symptoms, regardless of their LFT results. Some people, particularly those with health conditions that severely impair their immune systems, may remain infectious for longer.
WILL THERE BE MORE COVID VARIANTS?
There will but there is no way to know for sure when one will become a ‘variant of concern’, that spreads more rapidly, causes more-severe disease or evades immune responses. The evolutionary path and future of the virus remains unclear. There is hope that the current vaccines will prevent severe disease but it is not possible to rule out that the virus could evolve to be as infectious as Omicron and as virulent (severe) as the original strain.
HOW CAN I FIND OUR MORE?
There is more information in my earlier blog posts (including some in German by focusTerra, ETH Zürich, with additional information on Switzerland), from the UK Research and Innovation, UKRI, the EU, US Centers for Disease Control, WHO, on this COVID-19 portal and Our World in Data.