Many Kenyans may have had COVID-19 unknowingly during 2021

Researchers report that in 2021, samples from a number of pregnant women in Kenya tested positive for antibodies to the virus that causes COVID-19. This means they had been infected previously, or were infected at the time, but most of these infections had not been detected by polymerase chain reaction (PCR) test results. The researchers say COVID-19 prevalence may therefore have been underestimated in Kenya at the time.

In general, governments need accurate information about how many people may have the disease to put control and treatment measures in place.

In Kenya, many people didn’t go for COVID-19 testing however. This may be because the population is relatively young, and many had no symptoms or only mild symptoms. Scientists say that measuring the prevalence of antibodies to SARS-CoV-2 is one way to accurately estimate total infections.

Antibodies are specific proteins produced in the body in response to a particular disease, and their presence imply previous exposure or infection. 

In this study, researchers determined the prevalence of SARS-CoV-2 antibodies in pregnant women at 2 hospitals in Nairobi and Kilifi, Kenya. 

They tested for SARS-CoV-2 antibodies in blood samples from the women. They compared the number of positive samples they got with the number of PCR-confirmed SARS-CoV-2 infections they obtained from the Ministry of Health for the same areas. The researchers also reviewed health records and noted when samples were collected, as well as their age, residence, pregnancy trimester and the presence or absence of COVID-19 symptoms.

They found that half of samples in Nairobi tested positive for the SARS-CoV-2 antibodies, and between 1.3% and 10% in Kilifi. PCR-confirmed infections were less than 1% across both areas, meaning that the true number of infections were under-reported. They also found that only 7% of the women reported COVID-19 related symptoms, meaning that many infections were asymptomatic. 

The researchers suggest it may be better to use SARS-CoV-2 antibody tests to estimate the true numbers of infected individuals in Kenya.

They do caution however that they used anonymous patient data, and were thus not able to compare with other sources to validate their findings. 

The researchers also mentioned that they lacked data on loss of antibodies, which is important for estimating the total number of infections. 

This study was part of a bigger programme for monitoring SARS-CoV-2 using antibodies in Kenya, and was led by KEMRI Wellcome Trust Research programme.

Abstract

The high proportion of SARS-CoV-2 infections that remain undetected presents a challenge to tracking the progress of the pandemic and implementing control measures in Kenya. We determined the prevalence of IgG to SARS-CoV-2 in residual blood samples from mothers attending antenatal care services at 2 referral hospitals in Kenya. We used a validated IgG ELISA for SARS-Cov-2 spike protein and adjusted the results for assay sensitivity and specificity. In Kenyatta National Hospital, Nairobi, seroprevalence in August 2020 was 49.9% (95% CI 42.7-58.0). In Kilifi County Hospital seroprevalence increased from 1.3% (95% CI 0.04-4.7) in September to 11.0% (95% CI 6.2-16.7) in November 2020. There has been substantial, unobserved transmission of SARS-CoV-2 in parts of Nairobi and Kilifi Counties.

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