Coronavirus Society

Has Manaus reached herd immunity? Well, it’s complicated

Researchers suggested that Manaus, the largest Amazon city, attained “herd immunity” against Covid-19. But it’s too early to celebrate

Back in April, Manaus — the biggest city in the Amazon basin — became Brazil’s textbook coronavirus worst-case scenario. With insufficient measures to control the outbreak, infection curves exploded — leading the city’s fragile healthcare network to a full-scale collapse. At one point, morgues were simply unable to handle the sheer amount of bodies showing up at their door, literally left to pile up. Cemeteries ran out of coffins and space, with corpses buried in mass graves known as “trenches.”

Months later, things seem to have improved significantly in Manaus. New daily deaths dropped from 56 during the pandemic’s peak to 3.9 as of September 29. The few social distancing rules in place were lifted, and in-person classes returned at schools around the state of Amazonas. [restricted]

The spread of the virus slowed down so significantly that a group of researchers, led by scientists from the University of São Paulo, went as far as suggesting that Manaus might have reached a so-called “herd immunity,” which would have made it the first place in the world to obtain this desired mark.

By analyzing blood samples, the study claimed to have found coronavirus antibodies in as much as 66 percent of the population. This would suggest that, as more people gain immunity, it would become harder for the virus to infect new people and continue its spread.

“Though nonpharmaceutical interventions — as well as a change in population behavior — may have helped to limit SARS-CoV-2 transmission in Manaus, the unusually high infection rate suggests that herd immunity played a significant role in determining the size of the epidemic,” says the study — which has yet to be peer-reviewed.

And, indeed, controversy ensued once the paper was published. Jessem Orellana, a researcher from the Oswaldo Cruz Foundation in Amazonas, challenged the findings during an interview with cable news channel GloboNews. He said Manaus has experienced a sustained increase in new cases of acute respiratory distress syndrome (ARDS) over the past four weeks — and recommended another lockdown as the best way to avoid a massive second wave of infections and deaths.

“There is no doubt we are seeing a second wave in Manaus. We are having a high number of hospitalizations for severe cases of acute respiratory distress syndrome. (…) This is totally incompatible with a herd immunity scenario,” Mr. Orellana claimed.

And, as we reported in our Covid-19 Live Blog, Manaus Mayor Artur Virgílio Neto followed his advice — suggesting a new lockdown be put in place.

Covid-19 in Manaus, in numbers

According to the data provided by the Amazonas Health Surveillance Department (FVS), since the beginning of September, Covid-19 cases have been increasing in the city of Manaus. The seven-day rolling average of new cases jumped from 228.9 on September 1 to 307 on September 28. Hospitalizations rose in the middle of the month, but are now back to late August levels. 

The moving seven-day average for new daily deaths, however, remains below August levels, at around 3.6. 

In an interview with The Brazilian Report, Daniel Vilela, who coordinates the Oswaldo Cruz Foundation’s Scientific Computation Program, says that it is too soon to say whether Manaus or Amazonas state is undergoing a second Covid-19 wave, or whether it has reached herd immunity.

infogripe manaus coronavirus
Source: InfoGripe

“The pandemic is not over and we need to keep monitoring it. This behavior [in Manaus] could be just an oscillation. We must keep monitoring it instead of saying there is a second wave going on,” he says. 

In his view, the recent uptick in cases is significantly smaller than the peaks we saw at the beginning of the pandemic and the causes are yet unclear. “The state has lifted social isolation rules in recent weeks. When the share of the population that has been confined at home starts to circulate again, this could cause an increase in cases,” he notes, adding that further socioeconomic studies would be required to know whether the virus is now circulating among wealthier or more vulnerable populations. 

Regarding the possibility of herd immunity, Mr. Vilela explains that this depends on how long individual immunity to SARS-CoV-2 lasts, which remains unclear.

Data on hospitalizations show that, from September 7 to 21, there was a reduction in the number of vacant Covid-19 intensive care beds per every 10,000 adults in Amazonas state. The state has the lowest ratio in Brazil, with only 0.5 ICU beds for every 10,000 adults. However, of the beds that are available, occupancy rates remain reasonably low at 55.4 percent.

Speaking to The Brazilian Report, PR representatives of the Oswaldo Cruz Foundation said Mr. Orellana “does not speak for the institution” with regard to the epidemiological situation in Manaus. They added that the foundation will publish its findings “soon.” 

The Brazilian Report was unable to reach Mr. Orellana.

Government reactions to herd immunity claims

On September 10, the Amazonas Health Department (FVS) issued a statement claiming Mr. Orellana’s allegations are “groundless” and saying his attitude was disrespectful. However, the FVS did later confirm to The Brazilian Report that new case numbers increased by 12 percent between September 14 to September 25. It also says that if social isolation measures determined by the state government are not followed, “we may have a significant increase in the number of cases in the capital, which may cause a knock-on effect in other cities.” 

On Monday, however, Governor Wilson Lima posted a video on social media refuting the idea of a lockdown, even though his administration recently closed beaches, nightclubs and bars until October 26. 

“Our health department identified three deaths due to Covid-19 yesterday. It is a concerning situation but it’s not even close to the scenario we had in April and May. I don’t consider the chance of a lockdown at all,” said Governor Lima, adding that he would stick to plans of resuming classes in elementary schools on September 30.[/restricted]

By Natália Scalzaretto

Natália Scalzaretto has worked for companies such as Santander Brasil and Reuters, where she covered news ranging from commodities to technology. Before joining The Brazilian Report, she worked as an editor for Trading News, the information division from the TradersClub investor community.