High seroprevalence in the Peruvian population recovering from SARS-CoV-2 infection

Research by Antonio M. Quispe from the Centro de Investigación en Bioengineering of the Universidad de Ingeniería y Tecnología in Peru examined the infection rates in Iquitos, Peru, at different times in 2020.

The population seroprevalence was 70%, indicating that most people in the area were infected at some point and developed immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

By mid-2020, Iquitos, Peru, had the highest number of SARS-CoV-2 antibodies in the world. Despite natural immunity, the city experienced a second wave of coronavirus, with reinfections possibly due to the P.1 variant.

“The evidence suggests that the vast majority of Iquitos residents were infected with COVID-19 by July 2020. However, the transmission appeared to continue at a low level, as evidenced by a slight increase in seroprevalence in the test. Retest findings and such a high seroprevalence did not prevent a second wave from being triggered by a more dangerous variant of the virus. “

Their study was recently published in The Lancet Global Health.


Why Iquitos Peru?

At the time of the study, New York City had the highest seroprevalence, while other countries reported seroprevalence between 0.3% and 61.4%. In the absence of a COVID-19 vaccine, achieving herd immunity requires a seroprevalence of at least 70%.

Iquitos, Peru was selected because it was one of the hardest hit cities in the first wave – high numbers of infections and deaths plunged the public health system in just a few weeks.

How they did it

The researchers tracked people in Iquitos, Peru, from July to September 2020. They recruited participants from all four districts, including samples from 90,354 households.

Eligible participants were screened during the first week of each month. They also donated fingerprint blood samples to test for IgG and IgM antibodies specific to SARS-CoV-2.

The team also collected data on excessive deaths through the Peruvian National Death Register Information System.


The published results reflect data from July 13-18, 2020 and the one-month follow-up from August 13-18, 2020. The September 2020 data was incomplete as it was difficult to get participants to do a second follow-up.

A total of 716 participants were recruited in all four districts in the study. The representative samples also had a different group of participants based on gender and age. The average age of the participants was 29.2 years. About 51% of the participants were women and usually lived in the urban areas of the San Juan or Iquitos districts.

About 86% of the participants said they did not have any health problems. Those who suffered from illness reported heart disease, diabetes, chronic lung disease, obesity, and kidney disease. Four people were pregnant and one participant had Down syndrome.

Of the 716 participants, 70% had either IgM or IgG antibodies specific for SARS-CoV-2. The results suggest that the majority of people living in Iquitos, Peru, were infected with SARS-CoV-2 before July 2020.

Antibodies seemed permanent. After 1 month of follow-up, 66% were seropositive for IgM or IgG.

The seroprevalence varied according to age. People aged 60 years or older and children under 12 years of age had the highest seroprevalence rates.

The lowest seroprevalence came from the 18-29 group. However, this age group was also significantly less likely to test positive for COVID-19 after a month than participants under the age of 12.

Of the 87% who came for the 1-month follow-up, about 65% were retested and positive for COVID-19. There was a 2% incidence of new COVID-19 exposures.

The results showed that people who tested positive for IgG antibodies tested negative for reinfection after one month.

The incidence of new COVID-19 exposures was lower in people in urban areas than in rural areas.

“Our study estimates show that most Iquitos residents were infected with COVID-19 prior to our baseline intervention in July 2020. However, the transmission appeared to remain at a low level, as indicated by a slight increase in seroprevalence in the test retest results. Despite this high seroprevalence, both Iquitos and Manaus experienced second waves from January 2021, probably due to the emergence of the SARS-CoV-2 P1 variant in Manaus, which has higher transferability and reinfection rates, ”the researchers concluded.

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