A study in England reports that two-thirds of individuals with the omicron variant have previously had Covid.

• A new study has found that the omicron variant has largely replaced the previously dominant delta variant of Covid-19 in England.
• The Omicron variant, with its heavy mutations and high infectivity, has resulted in numerous infections in many countries.

A recent study reveals that the omicron variant has largely replaced the delta variant in Covid-19 cases in England, with most instances being likely reinfections.

The React study at Imperial College London, funded by the U.K. government, analyzed 100,607 PCR test results from across England between Jan. 5 and Jan. 20.

A study revealed that 99% of sequenced positive swabs originated from individuals infected with the omicron variant, while just 1% of infections were caused by the delta variant.

The study's authors reported in their paper released Wednesday that they observed unprecedented levels of SARS-CoV-2 infection in England in January 2022 and almost complete replacement of delta by omicron.

Reinfection capability

In January, 2,209 out of the 3,582 participants who tested positive for Covid-19 reported having previously tested positive for the virus. Additionally, 7.5% of infected participants said they believed they had previously had the virus but had not been confirmed through a test.

On Thursday, Imperial researchers warned that it is unclear how many of the results are due to reinfections or recent infections that have been detected again due to the sensitivity of PCR testing.

With the emergence of omicron, there is concern that a prior infection may not provide protection from reinfection, as U.K. health officials estimate that the risk of reinfection with omicron is 5.4 times greater than with the delta variant.

The highest Covid prevalence ever observed in the React study has been caused by the infectiousness of omicron, according to researchers who made this observation on Wednesday.

The research team stated that vaccination, including the booster campaign, remains the primary defense against Covid-19 due to the high levels of protection against hospitalizations.

If the high rates of omicron infection continue, additional measures may be necessary beyond vaccination, even though omicron seems to be less severe.

At least 171 countries have identified Omicron, a heavily mutated and highly infectious variant of Covid that has resulted in record numbers of cases in many countries.

Since the variant was discovered nine weeks ago, over 80 million Covid cases have been reported to the WHO, surpassing the total number of cases reported in 2020. Last week, an average of 100 cases were reported every three seconds, and someone lost their life to the virus every 12 seconds, as stated by Tedros, Director-General of the World Health Organization.

Although coronavirus infections in England decreased in early January, they later stabilized at a high level, with 1 in 23 people infected.

In the most recent study round, the percentage of positive test results increased threefold from December, with 4.4% of tests coming back positive.

On Tuesday, the U.K. recorded 94,326 new Covid cases and 439 deaths within 28 days of a positive test result. In late December, the country recorded 246,415 positive test results in one day, which marked the peak of Covid infections.

On Thursday, England will lift most of its remaining Covid restrictions, including the mandate for mask-wearing and the advice to work from home. With over 84% of its eligible population fully vaccinated against Covid and 63% having received a booster shot, the country is well-prepared to ease its restrictions.

BA.2 ‘variant under investigation’

The BA.2 omicron sublineage was responsible for 0.4% of positive test results, according to a study conducted at Imperial College.

The WHO reports that Omicron infections are made up of four subvariants, with BA.1 being the most dominant. However, recent trends in India, South Africa, and Denmark suggest that BA.2 is gaining popularity.

Despite a lack of cases, the U.K.'s Health Security Agency designated BA.2 a "variant under investigation," according to Sky News last week.

The study has been updated after Imperial College made changes to the pre-print.