The omicron variant is less likely to cause long COVID than the delta variant


Analysis by researchers from King’s College London of data from the ZOE COVID Symptom study app is published today in a letter to The Lancet. The findings are from the first peer-reviewed study to report on long COVID risk and the omicron variant.

Long COVID is defined by NICE guidelines as producing new or ongoing symptoms four weeks or more after the start of disease. Symptoms include fatigue, shortness of breath, loss of concentration and joint pain. The symptoms can adversely affect day-to-day activities, and in some cases can be severely limiting.

Researchers found the odds of experiencing long COVID were between 20-50% less during the omicron period versus the delta period, depending on age and time since vaccination.

The study identified 56,003 UK adult cases first testing positive between December 20, 2021 and March 9, 2022 when omicron was the dominant strain. Researchers compared these cases to 41,361 cases first testing positive between June 1, 2021 and November 27, 2021 when the delta variant was dominant.

The analysis shows 4.4% of omicron cases were long COVID, compared to 10.8% of delta cases. However, the absolute number of people experiencing long COVID was in fact higher in the omicron period. This was because of the vast numbers of people infected with omicron from December 2021 to February 2022. The UK Office of National Statistics estimated the numbers of people with long COVID actually increased from 1.3 million in January 2022 to 2 million as of May 1, 2022.

Lead author, Dr. Claire Steves from King’s College London, said, “The omicron variant appears substantially less likely to cause long COVID than previous variants, but still 1 in 23 people who catch COVID-19 go on to have symptoms for more than four weeks. Given the numbers of people affected it’s important that we continue to support them at work, at home and within the NHS.”

Analysis of self-reported outcomes confirms that, compared with the SARS-CoV-2 Delta variant, Omicron causes a different constellation of symptoms as well as shorter, milder disease.

In late 2021, the SARS-CoV-2 Omicron variant replaced the Delta variant in most countries. Although subjective experience indicated less-severe disease with Omicron than Delta, a robust comparison between the two variants has been lacking. In a prospective observational study, U.K. researchers analyzed data from 63,000 community-dwelling individuals who developed PCR- or rapid antigen-test–confirmed COVID-19 despite vaccination with two or three doses, and who regularly self-reported their symptoms using a smartphone app. In all, 4990 participants infected during Delta prevalence (June–November 2021) and 4990 infected during Omicron prevalence (December 2021–January 2022) were matched 1:1 regarding age, sex, and vaccination status.

Of the more-frequent symptoms, loss or altered sense of smell, sneezing, runny nose, brain fog, eye soreness, headache, fever, and dizziness were reported significantly more often during Delta prevalence, while sore throat and hoarse voice were significantly more often reported during Omicron. The three classic COVID-19 symptoms — fever, loss of smell, and persistent cough — were significantly less often reported by Omicron-infected individuals (odds ratio, 0.56). The duration of acute symptoms was longer for Delta than for Omicron (median, 8 vs. 5 days), the difference being less marked for those who had received only two doses of vaccine. Risk for hospitalization was lower during Omicron (1.9% vs. 2.6%).

reference :

What We Know about Omicron

CDC has been collaborating with global public health and industry partners to learn about Omicron, as we continue to monitor its course. We are continuing to evaluate how easily it spreads, the severity of illness it causes, and how well available vaccines and medications work against it.


The Omicron variant, like other variants, is comprised of a number of lineages and sublineages. The three most common lineages of Omicron currently are BA.1, BA.1.1 and BA.2.

The Omicron variant spreads more easily than earlier variants of the virus that cause COVID-19, including the Delta variant. CDC expects that anyone with Omicron infection, regardless of vaccination status or whether or not they have symptoms, can spread the virus to others.


Persons infected with the Omicron variant can present with symptoms similar to previous variants. The presence and severity of symptoms can be affected by COVID-19 vaccination status, the presence of other health conditionsage, and history of prior infection.

Severe Illness

Omicron infection generally causes less severe disease than infection with prior variants. Preliminary data suggest that Omicron may cause more mild disease, although some people may still have severe disease, need hospitalization, and could die from the infection with this variant. Even if only a small percentage of people with Omicron infection need hospitalization, a large volume of cases in a community could overwhelm the healthcare system which is why it’s important to take steps to protect yourself.


COVID-19 vaccines remain the best public health measure to protect people from COVID-19 and reduce the likelihood of new variants emerging. This includes primary series, booster shots, and additional doses for those who need them.

Current vaccines protect against severe illness, hospitalizations, and deaths due to infection with the Omicron variant. However, breakthrough infections in people who are vaccinated can occur. People who are up to date with their COVID-19 vaccines and get COVID-19 are less likely to develop serious illness than those who are unvaccinated and get COVID-19.


Scientists are working to determine how well existing treatments for COVID-19 work. Some monoclonal antibody treatments are less effective against Omicron’s BA.2 lineage, but continue to work against BA.1 and BA.1.1 lineages. Other non-monoclonal antibody treatments remain effective against Omicron. Public health agencies work with healthcare providers to ensure that effective treatments are used appropriately to treat patients.

. . . . .

There’s still a lot to learn about Omicron (BA.1) and its subvariants. One of those subvariants, BA.2, surpassed the original Omicron strain in March, only to be replaced by BA.2.12.1, another spinoff. In early June, two other Omicron subvariants, BA.4 and BA.5 were estimated by the CDC to make up 13% of new cases, up from 7.5% only a week before. The original Omicron strain was first identified in Botswana and South Africa in late November 2021, and cases quickly began to surface and multiply in other countries. By December, Omicron was causing daily case numbers in the U.S. to skyrocket to over a million.  

The Omicron subvariants have appeared to spread more easily than their predecessor. While early data has shown Omicron infections to be milder than previous variants, they have still caused hospitalizations and deaths, and scientists are still studying this.

How contagious is it? Omicron is more transmissible than Delta was—very early reports from South Africa showed cases rising rapidly from 300 a day to 3,000 a day over a two-week period. Omicron’s subvariants are considered to be even more efficient spreaders of the disease. One explanation is that more than 30 of Omicron’s mutations are on the virus’s spike protein, the part that attaches to human cells, and several of those are believed to increase the probability of infection. So, part of Omicron’s enhanced transmissibility may come from its ability to evade some immune responses, especially in individuals who were previously infected but not vaccinated. 

Severity: Data has suggested that Omicron is less severe, in general, than previous variants, according to the CDC. But it also says more data is needed to fully understand this variant’s potential to cause severe illness, hospitalization, and death, which can still occur. The CDC has noted that surges in cases may lead to significant increases in hospitalizations and deaths, as they did during the variant’s spread in the beginning of the year, when the estimated death rates went as high or higher than they were at the time of the Delta variant surge last autumn. More recently increases in Omicron infections were accompanied by a new increase in COVID-19 hospitalizations.

Can vaccination prevent it? The CDC says that while breakthrough infections in vaccinated people are expected, getting vaccinated and staying up to date with your vaccine and a booster shot is the best protection against Omicron. In March, while data was still emerging about how long the first booster shot will last, the U.S. approved second booster shots of one of the mRNA vaccines for adults ages 50 and older—and all adults who got the Johnson and Johnson vaccine and booster—giving them the option of choosing a fourth shot. A similar authorization was made for people with certain immune deficiencies. 


Delta (B.1.617.2) was first identified in India in late 2020; it soon spread throughout the world, becoming what was the predominant version of the coronavirus—until Omicron took its place in mid-December. 

How contagious is it? It’s estimated that Delta caused more than twice as many infections as previous variants—in Connecticut, it was estimated to have been 80 to 90% more transmissible than the Alpha variant. In the U.S., in June 2021, after a steady decline in COVID-19 cases and hospitalizations, the arrival of Delta coincided with a rapid reversal of that trend. In the fall of 2021, there were surges even in the most vaccinated states, prompting experts to urge people to get their booster shots.

Severity: Delta caused more severe disease than other variants in people who weren’t vaccinated. Early studies from Scotland and Canada, both cited by the CDC, suggested Delta was more likely to result in hospitalization in the unvaccinated. A report in the Lancet this past summer found that people in England had double the hospitalization risk with Delta than they did with Alpha, the previously dominant variant in that country. 

Can vaccination prevent it? All three vaccines in the U.S. were considered highly effective against severe illness, hospitalizations, and death from Delta. No vaccine is 100% effective, and Delta caused breakthrough infections in some fully vaccinated people. Also, infected vaccinated people could spread the virus to others, although likely they were infectious for a shorter time. 

Delta also prompted the CDC to recommend “layered prevention strategies” for both the vaccinated and the unvaccinated. That means that, in addition to staying up-to-date with their vaccines, people were advised to practice such strategies as washing hands, wearing masks, and maintaining a physical distance from one another, especially when indoors in places where there was substantial or high transmission.

Delta AY.4.2*

Delta AY.4.2, sometimes referred to—incorrectly—as Delta Plus, was actually the most prominent of a number of Delta offshoots, some of which had mutations new to Delta but that were found in other variants. AY.4.2 had two mutations to its spike protein, AY145H and A222V, that were considered to be key, but they were not located in a place where they would inhibit vaccines or treatments. This variant was thought to be slightly more contagious than Delta itself, but while Great Britain was tracking a steady rise of AY4.2, it did not rise as quickly in the U.S.

How contagious is it? While the data is limited, it was thought to be 10 to 20% more transmissible than Delta.

Severity: It did not appear to pose a greater chance of hospitalization or death.

Can vaccination prevent it? There was some evidence to show vaccines were effective against AY.4.2. Experts also recommended masking, physical distancing, and other mitigation strategies.

* AY.4.2  is technically an offshoot of Delta and not itself a coronavirus variant.


This variant, or B.1.351, was identified in South Africa at the end of 2020 and spread to other countries. Experts had been concerned about its several mutations and its potential to evade antibodies. Beta was not common in the U.S.

How contagious is it? The CDC said Beta was about 50% more contagious than the original coronavirus strain.

Severity: There was evidence to suggest that Beta may have been more likely than other variants to lead to hospitalization and death.

Can vaccination prevent it? South Africa stopped offering the AstraZeneca-Oxford vaccine (which is not available in the U.S.) early in 2021 after clinical trials showed it did not provide strong protection against mild and moderate disease from the Beta variant. Pfizer-BioNTech, Moderna, and Johnson & Johnson also reported less protection against Beta.


Alpha (B.1.1.7) was the first of the highly publicized variants. Alpha first appeared in Great Britain in November 2020 and infections surged in December of that year. It soon surfaced around the world and became the dominant variant in the U.S., where the CDC classified it as a variant of concern. Then, Alpha faded away with the rise of the more aggressive Delta variant.

How contagious is it? Some mutations in Alpha’s spike protein were thought to make it more infectious. The B.1.1.7 lineage was believed to be 30 to 50% more contagious than the original SARS-CoV-2 strain. In the U.S., in mid-April 2021—before Delta became predominant—Alpha comprised 66% of cases, according to a study released in June by the CDC.

Severity: Studies have suggested the B.1.1.7 lineage was more likely to land infected people in the hospital and was deadlier than the original virus.

Can vaccinations prevent it? Pfizer, Moderna, and Johnson & Johnson all said their vaccines were effective in preventing severe disease and hospitalization in Alpha cases.  

reference link :

More information: The Lancet (2022). … (22)00941-2/fulltext


Please enter your comment!
Please enter your name here

Questo sito usa Akismet per ridurre lo spam. Scopri come i tuoi dati vengono elaborati.