•Public health specialist Dr Richard Ayah calls for caution, saying the Kemri results were based on convenient sampling and may not be applied on the general population.
•Veteran chest health specialist Dr Joseph Aluoch says re-infection with Covid-19 is uncommon, suggesting that the presence of antibodies could confer at least short-term immunity.
About 2.6 million Kenyans already have the coronavirus, scientists suggest after testing donated blood for antibodies.
Antibodies are proteins made by the body to attack foreign substances such as viruses and bacteria.
Their presence in blood indicates the individual has ever been infected — even if that person never showed symptoms.
The prevalence of antibodies to the virus ranged from 1.1 per cent in blood donated in Uasin Gishu county to 12.4 per cent in Nairobi.
The researchers from the Kenya Medical Research Institute - Wellcome Trust tested blood donated across the country between April 30 and June 16.
"Antibody testing suggests many more Kenyans have already been exposed to Covid-19 than have been identified by surveillance activities," Kemri says in a policy brief, released early this week.
Kemri estimates about 550,000 people in Nairobi and roughly 100,000 in Mombasa, have already contracted and recovered from Covid-19, probably gaining some immunity.
Some could have been infected as early as March because the antibodies can linger in the blood for several months.
The numbers suggest that Kenyans should be seeing significant severe disease cases and deaths, but this has not yet happened.
At least 6,000 people should also have died from the disease countrywide, based on the current crude death rate.
"The large numbers of the population that have been exposed would lead models to predict significant numbers of severe cases and deaths. However, the county hospitals in which monitoring for pneumonia admissions is established are not seeing high numbers of admissions," the Kemri report said.
The researchers said they tested only 2,535 blood samples, and it is possible they over-estimated the number of people who have been exposed to Covid-19.
"Many more samples including sources outside blood donors are required to make confident conclusions," they said.
Normal PCR tests on throat and nose swabs only reveal active infection and cannot reveal people who have recovered from infection.
By July 1, the government had conducted only 173,355 PCR tests, out which 6,673 turned positive.
Public health specialist Dr Richard Ayah called for caution, saying the Kemri results were based on convenient sampling and may not be applied on the general population.
"There is no random sampling and the sample is taken from a group of people easy to contact or to reach. In this case it was from blood donors," he said.
Kemri acknowledged the shortcoming.
"The ideal way of estimating exposure to Covid-19 in the Kenyan population would be visiting randomly selected homesteads to collect and then test blood samples. This has not been practical under current restrictions," it said in the report.
Dr Ayah said the sample sizes are also too small for the results to be extrapolated to the wider population.
For instance, in Nairobi only 137 blood samples were tested for antibodies
"The power of study is diminished when the sample size is too small," he said.
Dr Ayah further noted the confidence intervals was too wide. This refers to the probability that a population parameter will fall between two set values for a certain proportion of times.
However, he says the results reveal important details.
"For instance, it appears most people with antibodies are outside Nairobi and Mombasa, which means the lockdown failed," he said.
Dr Ayah is the director of Science & Technology Park at the University of Nairobi and the director of the University of California at San Francisco programmes in Kenya.
Veteran chest health specialist Dr Joseph Aluoch said the presence of antibodies in so many people is a good thing.
He said re-infection with Covid-19 is uncommon, suggesting that the presence of antibodies could confer at least short-term immunity.
"It may prove there is some herd immunity. But we still don't know how effective that immunity is. It means the body mounted some soldiers against the infection, but we don't know how many they are, how strong those soldiers are and how long they will be there."
He said antibody tests also help determine the prevalence of a disease in the community, helping the authorities to mount the right approaches, for instance, whether to extend lockdowns, and physical distancing measures.
"For instance, we know Kenya has 1.5 million people with HIV because of antibody tests, and this has helped with the right approach," he said.
Kenyans wishing to take antibody tests privately may need to wait.
Lancet Pathologists said they have the capability but are waiting direction from the Ministry of Health.
"It is available at Lancet, but not yet offered to public as we are waiting for MoH to issue policy guideline on it," CEO Dr Ahmed Kalebi told the Star.
According to the World Health Organization, it is uncertain whether individuals with antibodies are protected against reinfection with SARS-CoV-2 (the virus that causes Covid-19), and if so, what concentration of antibodies is needed to confer protection.
There is also a chance that there is only a weak connection, or no connection at all, between antibody presence in the blood and protection against SARS-CoV-2.
This is because antibodies in the blood will have to find their way to the respiratory system — where the virus resides — to exert their protective functions.
Sometimes they do not end up in the lungs where they are most needed for protection.
(edited by owino)