New Brazilian Strain Of Coronavirus

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THE MANAUS STORY

A new COVID-19 strain in Brazil, also called the P.1., is spreading rapidly in the Amazonian city of Manaus.
In September, 2020, a study of COVID-19 antibodies in blood-bank samples from Manaus, estimated the presence of antibodies in 76% of the city’s population.
Back then, this had confirmed local rumours that Manaus had reached “herd immunity”.

COVID-19 infections surged by 125 % in Manaus between January 7 and January 22, according to the National Council of Health Secretaries and Brazilian media.
Hospitals in Manaus have been overrun and supplies of oxygen ran out.
The Brazil government had to airlift oxygen cylinders, after coming under pressure.

Perhaps the 76 % finding was wrong, and many fewer people in the city had been exposed to the disease than that much-talked-about study suggested.
Even before the second wave, there were some indications that the estimate — which was based on mathematical modeling on top of a basic sample set — might have been wrong.
- 76 percent would have been based above a crudely estimated herd-immunity threshold of 67 percent.
But herd-immunity estimates are rarely precise.
Even when the numbers precisely right, there is always a risk of “overshoot”.
Nearby Iquitos, in Peru, registered a similar attack rate of 70 percent.
The true observed sero-prevalence in the earlier survey – removing the anomalies of the basic sample set – was calculated to be 52 percent.
However, even taking that lower-bound estimate, should have produced significant-enough community protection to prevent an outbreak like the city’s second wave.

The immunity percentage measured by that earlier survey may already have reduced.
This means that a significant group of those people estimated to have immunity in October, had become vulnerable to infection again.
Previous studies have found, protection against COVID-19 lasting at least as long as six months after exposure.
Since the second wave in Manaus, was seven to eight months after the first, it suggests the possibility that the shelf life of naturally acquired antibodies could be only six months.
Protection would drop fairly rapidly,
This has raised fears that at those infected in early waves in Wuhan, Lombardy, New York, and London may be vulnerable to infection already.

The new variant, like those discovered recently in the U.K., South Africa, and California, is more transmissible than the strains that have dominated the pandemic thus far.
This one could have gained an even larger transmission advantage, since the Brazilian variant took over the pandemic in Manaus much faster than the U.K. strain did the British pandemic.
This would mean that the level of acquired immunity in the population would have to be higher to offer herd immunity protection — perhaps more than 80 percent.
The disease might be working much more quickly through that relatively small slice of the population.
Because of the dynamics of exponential growth, when transmission accelerates like this it also creates many more deaths.

The new strain has achieved a more total “immune escape,” in addition to being more transmissible.
This means it could evade antibodies produced by exposure in the first wave and infect again.
So, even those people who had mounted a robust immune response, and would have seemed safe – are at risk of re-infection.
The antibodies had not waned, they had just been made ineffective.
This is scarier than the possibility of waning transmission (2^nd possibility), because at least under that theory, antibodies offer protection for a period of time.
This is scarier than enhanced virulence, because it means that existing antibodies could offer little protection, or perhaps no protection at all.
The disease will progress through the community a second time just as quickly and devastatingly as it did the first time.
Vaccines are still useful against new strains with somewhat diminished immune response.
However, across populations the effect can be quite profound.
If efficacy falls to, say, 75 percent when herd immunity requires that 80 percent of the population demonstrate protection, then we cannot achieve population-scale protection through vaccination alone.

There is no research yet into the efficacy of any of the vaccines against the new Brazilian variant.
However, in Israel, the world’s most effectively vaccinated country, officials are worrying over stubbornly persistent infection rates.
This is because, while their vaccines do offer at least some protection against the British variant particularly, it may not be enough to quickly control the pandemic, even with their gold-standard vaccine deployment rates.

In the just-released clinical data for Johnson & Johnson’s much-anticipated single-dose vaccine, efficacy against transmission was 72 percent in the United States, primarily against the classic strain, but dropped to just 57 percent in South Africa, where the new local variant was dominant.
If the Manaus experience is explained by waning antibodies, that could mean that nations in the developing world would pass through six or eight full pandemic cycles before vaccines arrive at scale.
If it is explained by immune escape, it would mean that this new variant would tragically reset the clock on all naturally acquired immunity wherever it traveled.
- Populations would have to start from scratch, but could build up natural immunity over time.