Your questions, our answers | The Omicron boomerang

All those who have received Omicron particles as a Christmas present see spring coming with less serenity than they would have liked… Should we fear a reinfection? Is this the right time to finally receive the booster dose? Update on the state of scientific knowledge.

Judith Lachapelle
The Press

“Like millions of Quebecers, I received COVID-19 as a Christmas present and I guess it’s the fault of the Omicron variant. So I thought I would have peace for several months thanks to my dashing new antibodies… But what do I hear? Can we be reinfected by the same variant? »

In effect. This was also the case with the other variants, but data suggest that the reinfection rate is higher with Omicron.

In the United Kingdom, authorities have compared the number of reinfections that occurred during periods when different variants were circulating. It was measured that during the period from December 20, 2021 to March 20, 2022, when Omicron was the dominant variant, the risk of reinfection was approximately 10 times greater than during the period when Delta was rampant, i.e. between mid-May 2021 and the December 19, 2021.

“The risk of re-infection with Omicron is much higher than with any other variant so far,” the UK’s Office for National Statistics said this week. An infection with Omicron is therefore less immunogenic – it generates a lower level of neutralizing antibodies – than an infection with Delta, and it protects less against reinfection or against infection with a future variant.

But beware: the drop in the level of neutralizing antibodies does not mean that the immune system has completely forgotten how to fight the enemy. Other memory cells also play a key role in fighting infection.

“Okay, so I can be re-infected at Omicron. What are the risks of this happening to me? »

All is relative. In a prepublished study at the end of February, researchers from Qatar evaluated that an infection with the BA.1 subvariant (the one that circulated during the fifth wave) protected 95% against an infection with the BA.2 subvariant (the one that is now dominant around the world). For about two million Quebecers who caught Omicron at the start of the year, that still leaves 100,000 people who could be reinfected.

The risk of reinfection depends on several factors, but especially on the vaccination status. “Those who are not vaccinated are more likely to be re-infected than those who are vaccinated,” British statisticians said this week. Vaccines are not 100% effective either – if they protect very well against severe forms (80% for two doses), they protect a little less well against mild forms of infection.

But if, unfortunately, a reinfection occurs, the risk of it escalating into serious illness is lower than with the first infection, says the D^r Nicholas Brousseau, from the Quebec Immunization Committee (CIQ). “Often it’s the first infection that can be very dangerous,” he says.

“I had COVID-19 over the holidays, before I got my booster shot. In January, Public Health recommended that people in my situation wait three months before getting vaccinated again. Here we are in April. Should I finally get that booster shot? »

It all depends on who you ask. At a press conference on Friday, Canada’s Chief Public Health Officer, Dr.^D Theresa Tam, said “it’s not too late to get your booster shot”. All adults should get it, even those who have been infected, she said.

In its opinion of March 23, the CIQ still considers that a person who is not immunosuppressed, who has had two doses of vaccine and an infection confirmed by a test (rapid or not) “during the period when the Omicron variant was predominant” has “adequate protection”. These people can, if they request it, receive a booster dose three months after infection. Otherwise, they can wait for the next vaccination campaign that Public Health plans to hold next fall.

The D^r Brousseau mentions a few elements to help in decision-making.

First, age and state of health.

Then, you have to take into account his tolerance to the possibility of being reinfected. A first infection with Omicron already protects well against reinfection, and protects even better against the risk of severe forms. If you want to avoid re-infection as much as possible, a booster dose will provide additional protection. “The third dose makes a good difference to avoid being reinfected, even if it is not perfect either”, recalls the D^r Brousseau.

Remember that for adults who have had two doses of vaccine and who have not had COVID-19 since last December, the opinions are the same from one end of the country to the other: the booster dose is strongly recommended. For those under 18, regardless of whether they have been introduced to Omicron or not, the booster dose is only recommended for those who are at risk of severe complications.