Highlights
- Much is already known about Omicron, including the sub-variants.
- But much is yet unknown, including the overall risk of repeat infections, following a primary illness.
- It’s a fast-moving target: studies indicate prior COVID-19 infection does not fully protect people against re-infection.
Is Omicron reinfection possible? If so, how many times can it happen to a person? Experts now say the new strain may infect the same person twice, which means the chances of reinfection are high.
Getting sick once with Omicron, recovering from the illness — and getting that same illness again later — is something health experts are closely watching now.
Omicron was discovered only in November 2021, but has quickly become the dominant strain. Dr Gregory Poland, an infectious diseases expert and head of Mayo Clinic's Vaccine Research Group, says “the chance of getting reinfected with Omicron is almost 5½-fold higher than reinfection with Delta."
Generally, a COVID infection bestows immunity against reinfection for at least six months, say experts. But in the case of Omicron, the protection against reinfection drops to around 19 per cent, Imperial College London researchers said. Of course, the immune response is linked to a person's health, and the risk is much higher among the immunocompromised.
US epidemiologist Eric Feigl-Ding says an Omicron reinfection is possible “if the first Omicron infection was of a 'low-dose' that did not stimulate the immune system enough”.
What we’ve gathered so far:
What is reinfection?
Reinfection is the second COVID infection, irrespective of the COVID strains involved. Data suggests that reinfection is higher among the unvaccinated and those whose first infection was mild, resulting in an inadequate immune response.
The UK Health Security Agency defines reinfection as a COVID case 90 days or more after a previously confirmed infection. That excludes people who shed the virus for a longer duration after the first infection.
What do we know about reinfection with Omicron?
Due to the high number of mutations, especially on the spike that’s used to latch on the human cell walls, Omicron is highly contagious. That has resulted in a new wave of infections. Some of them are reinfections.
According to Stanley Weiss, professor at the Rutgers New Jersey Medical School and the Department of Epidemiology at the Rutgers School of Public Health, you can get Omicron twice.
South Africa has reported several cases of Omicron infection among people who have recovered from COVID. Although these are anecdotes, US epidemiologist Feigl-Ding says it’s possible.
Mayo Clinic’s Dr Poland attributed to this is due to the increased transmissibility of Omicron and the waning immunity from vaccine or infection over time.
A South Africa preprint study suggests that Omicron is more than three times more likely to reinfect people than other variants. Researchers say this may be due to Omicron’s ability to evade prior immunity.
What are the risk factors? More common in what age group?
Most of the reinfections have been among the unvaccinated and people with comorbidities (underlying health conditions). At least one South African study suggests that Omicron can evade the human immune response. But that needs to be confirmed by more studies elsewhere. So experts think two doses of a vaccine will protect against severe illness by Omicron.
A study by the Imperial College London shows that among 18 to 29-year-olds residents in London, and those of African ethnicity have significantly higher infection rates with Omicron than Delta.
The risk varies from person to person. Factors like the severity of the first COVID infection, the variants, and individual immune response play a role, says William Schaffner, infectious disease specialist and professor at the Vanderbilt University School of Medicine.
What do we know so far about the Omicron sub-variants?
The UK Health Security Agency has designated BA.2 Omicron sublineage a “variant under investigation.” The Imperial College London also study found some recent infections in the UK were caused by the BA.2.
Omicron infections stem from four subvariants, according to the World Health Organisation. The BA.1 lineage is the most dominant, but trends in some countries indicate that BA.2 is becoming more prevalent.
How common is COVID reinfection?
An early evidence of COVID reinfection was published in August 2020 when a young and healthy patient was diagnosed 4.5 months after the first episode.
Researchers at the University of Hong Kong suggested then that immunity to the virus may last only a few months in some people. Another study published April 2021 in The Lancet (Respiratory Medicine) indicates reinfection by SARS-CoV-2 in healthy young adults was “common”.
It also shows prior COVID-19 infection does not fully protect people against re-infection, according to Dr Stuart Sealfon, Professor of Neurology at the Icahn School of Medicine at Mount Sinai and senior author of the paper.
His observation was based on records from more than 3,000 young, healthy members of the US Marines Corps analysed by Icahn School of Medicine at Mount Sinai and the Naval Medical Research Center.
“Despite a prior COVID-19 infection, young people can catch the virus again and may still transmit it to others,” said Dr. Stuart Sealfon.
▶ Reinfection: subsequent infection, confirmed by PCR swab test.
What are the odds of severe disease at reinfection?
One extensive study published December 23, 2021 in the New England Journal of Medicine (NEJM) was based on data of 353,326 persons with PCR-confirmed “primary infections”.
One of the key findings: no cases of death from COVID-19 at reinfection. Overall, it showed reinfections had 90 per cent lower odds of resulting in hospitalisation or death than primary infections.
And there were no cases of critical disease at reinfection — though there were 28 cases at primary infection.
In this study, which used population data in Qatar, there were no cases of death from COVID-19 at reinfection and 7 cases at primary infection. For reinfected persons, the median time between primary infection and reinfection was 277 days.
The good news: reinfections were generally “mild”, said researchers. They explained it was perhaps due to the “primed immune system” after primary infection.
▶ CRITICAL: Critical disease is one that leads to hospitalisation in an intensive care unit (ICU).
What does the latest medical literature say about reinfection with Omicron?
In a new study, Imperial College London researchers conducted 100,000 valid swab tests self-administered by a random sample of people across the UK between January 5 and 20, approximately 4,000 showed a positive result — and nearly 3,600 of those individuals specified they had had COVID before.
“Past infection was associated with high risk of reinfection with Omicron,” the study’s authors noted in its abstract.
This is seen as further evidence of the strain’s “immune escape” capability among those previously infected.
Is it possible to get Omicron twice?
“Yes, you can get Omicron twice,” according to Dr Stanley Weiss, professor at the Rutgers New Jersey Medical School and the Department of Epidemiology at Rutgers School of Public Health.
“Omicron is highly contagious and it would appear to not induce fantastic protective immunity,” Dr Weiss was quoted as saying.
How common is Omicron reinfection?
It’s not known yet at this point. The variant is fairly new. But there are a number of things already known so far about the variant:
▶ Since the variant was reported in November 2021, it has quickly become the dominant strain, proving its hyper- transmissibility, thus allowing it to quickly overtake all other variants in so short a time.
▶ It evades immunity better than any previous variant, including Delta.
▶ The variant is less severe even for unvaccinated, according to a study conducted by the National Institute of Communicable Diseases (NICD) in South Africa.
▶ Several Omicron-related studies essentially show the variant was less likely to lead to hospitalisation than those infected with Delta.
▶ It survives longer on plastic and skin than prior variants.
▶ Anecdotal evidence is emerging that points to cases of reinfection following a recent Omicron infection.
