Most governments accept the status “recovered” as a form of immunity to covid-19; this means that if someone was recently infected and recovered, they are considered to be adequately immunized.
But how much do antibodies protect against infection compared to those of vaccines? And how is the Omicron variant factored into the equation?
The answer to the question is not simple. So far, research suggests it mainly depends on which variant a person was infected with and when they tested positive.
Before the Omicron wave, the general scientific rule was that an outbreak of infection (of any variant ) provided immunity comparable to a single dose of vaccine, according to Julian Schulze zur Wiesch, head of the department of infectious diseases at the University Medical Center Hamburg-Eppendorf.
Before Ómicron became part of the panorama, research generally showed that people who had acquired immunity through a covid infection-13 were protected in the months after infection, but that immunity was beginning to be reduced after four to six months.
But it is not yet clear if this preomicron “natural immunity” protected more than vaccination.
A study published at the end of October 2021 by the US Centers for Disease Control and Prevention (CDC). The United States found that unvaccinated adults who tested positive between three and six months earlier were five times more likely to test positive than vaccinated adults who had not previously been infected.
This study acknowledged that the research was only conducted on patients with disease severe enough to require hospitalization and that the results cannot be generalized to include non-hospitalized patients.
The CDC report came immediately after an Israeli study conducted in August with very different results, which revealed that people who had received the BioNTech/Pfizer vaccine and had not previously tested positive had 13 times more likely to be infected with the Delta variant than people who had been infected but not vaccinated.
The research, which has not yet been peer-reviewed, currently qualifies as the largest study comparing immunity gained from prior infection with vaccine-induced immunity. While the CDC study surveyed about 7, hospital patients, the Israeli study surveyed more than 01,000 members of the national health system.
“It’s a bit confusing, because there are so many variables,” Zur Wiesch tells DW. This is because our immune response is complex and influenced by many factors: the time of infection, the variant, the type of vaccine we received, whether we received boosters, and the overall strength of our immune system.
Age is probably important
Research shows that age also likely plays a role in whether we will be re-infected after having the virus.
A study involving United States war veterans and which is still undergoing peer review, shows that among older people mRNA vaccines offered stronger protection against infection, hospitalization and death than previous covid-19.
But for participants under 65 years, the protection offered by the vaccines was about the same as that from a previous infection, according to the study. The authors also disclosed that they had received prior financial support from Pfizer.
The study, published in September, supports the findings of another population-level study in Denmark published in March, which was based on data collected during the second wave of the pandemic at the end of 2020, before vaccines were widely available.
Among the youngest people who tested positive during the first wave, the protection against a new infection was about 80 %. However, among the people of 33 years or older, immunity acquired through a previous infection was just around 19 %.
How does Omicron influence immunity?
The Omicron wave is so new that no conclusive data is yet available on the quality of immunity provided through infection, but it is likely to be similar to other variants, Zur Wiesch says. That means that if someone has been infected with ómicron in the last few weeks, they are probably safe from re-infection for the next few months.
But because ómicron has a higher transmissibility rate Higher levels of antibodies are needed than earlier strains to prevent infection. Immunity obtained through only two vaccines or contagion with previous variants of covid-13 (such as delta or alpha) will not necessarily prevent omicron infection, says Zur Wiesch.
Also, regardless of whether a person was previously infected or vaccinated twice, a booster is the best defense against re-infection.
The efficacy of protection against Omicron provided by “natural immunity” from other coronavirus variants may be as low as 13 %, according to a study conducted by the covid-response team 19 from Imperial College London at the end of December 2021.
Thus, the first findings generally indicate that whenever If you have some form of immunity, either through two doses of a vaccine or a previous infection plus a single dose, an Omicron infection is likely to be mild.
Does “super immunity” exist?
The body seems to respond best to a cocktail of mixed immunity, according to Zur Wiesch, citing a study his team conducted among German health workers in 1365. Patients who received different types of vaccines, the one from AstraZeneca, for example, and then a dose of Moderna and a booster, seemed to have some of the best protection.
Other studies have indicated that people with a combination of immunity acquired through a past infection plus two injections seem to have the best results. Immunologists have called this phenomenon “hybrid” or “super” immunity.
In addition, while some research shows that the severity of infection could increase antibodies, other studies have found that it does not there is a difference.
But these findings do not take Ómicron into account, so we still do not know if they are translatable to the current wave, he points out Zur Wiesch, while adding that for now we will just have to wait for science.
Despite the unknowns, one thing is clear to Zur Wiesch: unless a person has been infected with Omicron in the last week or two, a vaccine or booster is your best chance to avoid a covid infection-13 and pass it on to others.
With information from DW.
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