If I’ve been infected with Omicron, what is my risk of catching it, or another Covid variant, again?
It is now clear that it is possible to catch Covid more than once, including strains you have previously been infected with. It is also known that being infected with Covid-19 boosts your protection from reinfection. What is less clear is how long that extra protection against the same strain lasts – and whether it is as effective against other strains.
A small laboratory study published in December suggests one reason Omicron is replacing Delta is that being infected with Omicron offers a high level of protection against Delta, while the reverse is not true.
Dr Maria Van Kerkhove, the Covid-19 technical lead with the World Health Organization’s health emergencies program, said another reason for a sharp increase in Omicron cases in recent weeks was its potential for “immune escape”.
“This means people can be reinfected either if they had a previous infection, or if they’ve been vaccinated,” she said.
“Now you have to remember, vaccines are incredibly effective at preventing severe disease and death, but they don’t prevent all infections and they don’t prevent all onward transmission. So it is still absolutely critical to get vaccinated because it will save your life, but it doesn’t prevent all infections or transmission.”
How long could protection from infection last?
Kirby Institute virologist Associate Prof Stuart Turville said Omicron has only been around a couple of months so it was too early to estimate the risk of reinfection or how long any protection from an infection lasts.
“We can only base our answer on what we have observed in previous variants,” he said. “Several large studies from Qatar have looked at reinfections.”
A recent preprint from Qatar states: “Protection afforded by prior infection in preventing symptomatic reinfection with Alpha, Beta, or Delta is robust, at about 90%.
“While such protection against reinfection with Omicron is lower, it is still considerable at nearly 60%. Prior-infection protection against hospitalisation or death at reinfection appears robust, regardless of variant.”
How long this protection lasts is unclear and depends on factors including the number of vaccinations, whether you’re immune-suppressed, and the length of time since vaccination.
If I caught Delta last year and am also double-vaccinated am I safe from Omicron?
Turville said a complicating factor to immune response is the severity of any Covid-19 infection. His research team are examining people infected with Delta in late 2020 onwards to see how their antibodies hold-up post-vaccination.
“If you were infected and then vaccinated with two doses of either AstraZeneca or Pfizer, your response is very similar to three doses of Pfizer,” he said.
“But that’s assuming you have a decent response to the virus initially. If you have had an initial low response to the virus, your response will be driven more by the vaccine dose. As a broad brushstroke, if you had a mild case of Covid in 2020, your response will be relatively low. If you had a case that made you very sick, so high disease severity, you will have had a better response.
I’ve had two vaccine doses and I caught Covid. Do I really need a booster, and if so, how soon after infection?
There is no need to delay vaccination. Health guidelines state you can get a booster once you have fully recovered from the virus, which for most people is four-to-six weeks after infection. In the short-term boosters can further strengthen your protection up to 86% against reinfection and 98% against serious illness, NSW Health states.
The independent expert advisory group on vaccination, Atagi, says the same thing, and that “previous infection is not a contraindication to vaccination … vaccination can occur following recovery of acute illness from Covid-19”.
Atagi also decreased the maximum timeframe allowable for deferral of vaccination after Covid infection from six months to four months but suggests those with very severe Covid cases should check with their doctor. Atagi decreased the timeframe “due to the increased risk of re-infection with the Omicron variant, particularly for those who had a Delta variant infection in 2021,” the guidelines state.
Turville said viewing Omicron as a “natural booster” making a third vaccine dose unnecessary was unwise.
“That exercise is an uncontrolled experiment where you will have no control of the dosage, or in other words the level of viral infection, and thus the outcome,” he said. “Vaccination is a set dosage that is safe with a predictable response in most people.”
I’m triple-vaccinated and caught Covid. How soon after recovering can I catch Covid again?
“It is a great question but one we will likely only know in the next few months,” Turville said. “In brief, we do not know as the numbers of people in that setting are on the low side and it will take a while to study in cohorts where people have volunteered for researchers to follow their response. The other issue is this will change with future variants.”
I’ve just recovered from Covid and finished isolating, and I’m vaccinated. I’m now a close-contact of someone with Covid. Do I really need to isolate again?
The advice is similar in each state and territory.
In Victoria, if a recently recovered Covid-19 case becomes a close contact of a confirmed case, they do not need to quarantine again if the re-exposure was less than 30 days since the recovered case’s onset of symptoms, or since their first positive test if they had no symptoms.
In the ACT, if you are identified as a household or high-risk close contact, or a moderate risk casual contact within four weeks of your clearance from isolation, you do not need to isolate again.
The ACT advice states if you have recovered from Covid while there is still someone in your household who has it, you can leave the house, but must separate from other people with Covid-19 in the household as much as possible and observe hand hygiene, mask wearing and social distancing as per public health advice.
Queensland Health advice states that you are not a close contact if you have had Covid-19 in the past four weeks.
It is best to check with your state or territory health department if you are unsure, and for definitions of “close contact”, which have changed over time.