As the COVID-19 epidemic evolved, presentation of the disease changed substantially.

Due to vaccination, increased natural immunity and new variants, there is a substantial decrease in severe cases, making it difficult to recruit new patients.

In this study, the investigators will explore the reasons for the apparently lower proportion of severe COVID-19 cases in many sub-Sahara African countries. Indeed, despite fragile health care systems, the burden of COVID-19 on the African continent seems substantially lower than initially feared. Many potential reasons for this discrepancy have been formulated: the different population age structure, experience of African nations with previous pandemics, warmer climate, and genetic preposition. However, another compelling hypothesis is that of trained immunity by endemic pathogens, such as plasmodia. According to this hypothesis, innate immune activation by endemic pathogens would prime a more robust initial innate immune response to SARS-CoV-2 and could therefore protect against severe COVID-19.

To explore this, the investigators propose conducting a case-control study in Kinshasa, in the Democratic Republic of the Congo (DRC). Kinshasa is an area with mixed prevalence of malaria and the area in DRC most affected by COVID-19. In this setting, the investigators will compare cases of severe COVID-19 with controls that have non-severe COVID-19 and that are matched for age, sex, and health zone. The aim is to compare pre-existing immunity against malaria, both cellular and humoral between the two groups.

INCLUSION CRITERIA

To be eligible, study patients must meet the following criteria:

For cases:

• Be at least 18 years of age

• Have an RT-PCR or Antigenic Rapid Test confirmed SARS-CoV-2 infection within 72 hours prior to inclusion.

• Have given informed consent or that of their guardian/ representative to participate in the study.

• Diagnosed as a severe COVID-19 case according to the following criteria:

  • Presenting clinical signs of pneumonia: fever, cough, dyspnea or crepitations AND
  • Presenting at least one of the following signs:

Respiratory rate > 30 cycles/min OR Severe respiratory distress or SpO2 < 90% on room air

• Be admitted to a care unit for COVID-19
• Residing in the health zone for at least 6 months

For controls:

• Be at least 18 years of age

• Have a PCR or Antigenic Rapid Test-confirmed SARS-CoV-2 infection within 72 hours prior to inclusion

• Have given informed consent to participate in the study

• Diagnosed as a non-severe COVID-19 case according to the following criteria:

  • Be asymptomatic OR
  • Symptomatic, but no evidence of severe pneumonia Respiratory rate > 30 cycles/min OR Severe respiratory distress or SpO2 < 90% on room air

• Reside in the study health area for at least 6 months

• Recruited within 10 weeks following the matched cases

EXCLUSION CRITERIA

To be eligible, study patients cannot meet the following criteria for cases and controls:

• Subject has a contraindication to venipuncture, as determined by clinical judgment
• Subject is vaccinated against SARS-CoV-2
• Subject has been infected with SARS-CoV-2 in the past and now presents with reinfection

This case-control study will be conducted in the Republic of Congo in the city of Kinshasa, the epicenter of COVID-19. Kinshasa is a malaria endemic area, the distribution of malaria prevalence is lower in urban areas compared to peri-urban areas. Indeed, the city of Kinshasa is structured in four health districts and sixteen hospitals, distributed in the thirty-five Health Zones for the management of COVID-19.

The study will consist of cases and controls:

• Cases will be severe COVID-19 cases that will consist of patients hospitalized and recruited in COVID-19 Treatment Centers.
• Controls will consist of asymptomatic or symptomatic cases without signs of severity. For each case, two controls will be recruited after having been matched in terms of age, gender and health zone of origin.

no adverse events or deaths collected as it is not applicable (no investigational product)

no adverse events or deaths collected as it is not applicable (no investigational product)