In the state of Brazil, a sign of Omicron’s key advantage | Latest India News

New Delhi:

Scientists have uncovered most of the secrets of the Omicron variant (as well as sister lineages such as BA.2), especially those with the most real-world consequences: the variant spreads faster than any before it, but is much less likely to lead to serious illness. It’s the most resistant to past immunity, but vaccines still work to prevent deaths.

What is not known is how many of these traits are intrinsic to the virus, compared to the characteristics that are the consequence of baseline immunity in the world’s population in what is now the start of the third year. of the pandemic.

Among the specific unknowns is why the Omicron variant is spreading as quickly as it does.

The first theory that sought to explain this came from laboratory studies that showed the virus multiplied more easily in certain parts of the respiratory system known as the bronchi and thrived more widely in the upper respiratory tract. This, it was believed, allowed the virus to occupy tissues that gave it the advantage of being exhaled or expelled.

A second theory was that the virus was causing far more asymptomatic infections, which meant it was more easily spread by people who were simply unaware of their infection.

A third theory, which has been talked about since the early days of the Omicron outbreak, is that the virus spreads more easily because it can infect more people, even those who have already been infected or vaccinated due to its improved resistance. .

Now, a Brazilian study gives more credence to the third theory.

The case of Amazonas

Researchers from Brazil’s Oswaldo Cruz Foundation, or Fiocruz, found that in the Brazilian state of Amazonas, the Omicron variant triggered a record wave of infections even when the population had baseline immunity that managed to prevent the Delta variant to settle down.

Amazonas, home to the city of Manaus – one of the most densely populated places in the world – experienced two outbreaks in early 2020 and early 2021. Its first outbreak was caused by the B.1 lineage, the most close to the virus that spread in the first year of the pandemic around the world, and the second driven by the worrying P.1 variant.

Both epidemics were large and most of the population was infected during these waves, and there was also high vaccination coverage. “The high prevalence of individuals with hybrid (natural or vaccine-induced) immunity in this Brazilian state successfully limited the previous expansion of Gamma plus (P.1.) and Delta (B.1.617. 2/AY.) that emerged and spread during the second half of 2021 in Amazonas,” the Fiocruz team wrote.

Consequently, the virus circulated at a roughly steady level of around 50 to 500 positive cases per day (seven-day rolling average) from early May to late December 2021, they said.

But, in January, “the average daily number of Sars-CoV-2 positive cases in the Amazon rapidly increased from 90 to 6,500, coinciding with the global spread of the immune evasion COV (worrying variant) Omicron (B .1.1.529 /BA.*),” they added,

In their assessment, the scientists added that hybrid immunity “could not, however, prevent a further expansion of Sars-CoV-2 cases associated with the spread of the Omicron variant that combined both enhanced transmissibility and immune evasion. substantial”.

In other words, they think the virus has an intrinsic advantage over transmission and also finds new hosts because previous infection is not enough protection.

“Despite the record number of positive cases recorded in Amazonas in January 2022, the proportion of deaths during the Omicron wave is currently much lower than that recorded during previous epidemic waves or the previous endemic-like period,” they said. .

“This observation is consistent with the notion that acquired immunity (natural plus vaccines) effectively reduces the mortality rate from Sars-CoV-2 infection in Amazonas over time,” they added.

It is likely that Omicron’s immune evasion is strong enough to cause reinfections. Immune resistance, it is now clear, is not strong enough to trigger more severe disease.

This very trait could also explain the second phenomenon described at the beginning: asymptomatic infections. While asymptomatic infections pose an epidemiological challenge in contact tracing and isolation, with Omicron this reflects a positive – the coronavirus in this configuration is now milder, either due to baseline immunity or evolutionary traits intrinsic. Or, maybe, both.