In an analysis marking two years since Nigeria’s first Covid-19 case, the Guardian discussed a study of how many people in the country had been infected with the coronavirus.
The study found that 50% of the population had Covid-19 antibodies, it said, meaning they had been infected. But this is incorrect, as the study hasn’t been completed.
The analysis was correct to say that 50% of Nigerians have survived the virus. Other data indicates a survival rate of 80%.
Infections are ticking up again in some African countries, such as South Africa.
The paper’s analysis made two interesting claims. Early results of a national study, it said, showed “that over 50% of Nigerians have been exposed to the virus, and have antibodies for Covid-19”.
It went on: “In other words, over 50% of Nigerians have survived the virus …”
Is this all correct?
The journalist who wrote the article told Africa Check the claim came from a Nigeria Centre for Disease Control (NCDC) study. He said he had also quoted Dr Chinwe Ochu, who leads the centre’s prevention programmes and knowledge management.
In February 2021 the NCDC and its partners released the findings of a survey done in four states. This seroprevalence study sought to find the real extent of coronavirus infection in Nigeria, the researchers said.
“Results coming in show that over 50% of the population have antibodies for Covid-19, meaning that they have been exposed to the virus,” the analysis quoted Ochu as saying.
Study of Covid burden ‘still ongoing’
But Dr Yahya Disu, the NCDC’s head of risk communication, told Africa Check that Ochu had not made a conclusive statement about the survey’s results.
“The study is still ongoing,” he said. “It has been conducted in only about six states and the results vary significantly. So, it is not correct to conclude that the study found that over 50% of Nigeria’s population has been exposed to Covid-19 and has developed antibodies for it."
What are seroprevalence studies?
The Nigeria Centre for Disease Control is running seroprevalence surveys to estimate the true burden of Covid-19.
According to the World Health Organization, seroprevalence studies are done to measure the extent of infection in a population under study, as shown by antibody levels. They provide data on asymptomatic or under-reported infections that may have been missed by routine diagnostic testing.
Antibodies against Sars-CoV-2 – the coronavirus that causes Covid-19 – can usually be detected in the first few weeks after infection or vaccination. Their presence indicates that a person was infected with the virus.
So what did the NCDC’s study actually find?
The NCDC survey collected blood samples from more than 10,000 people in Lagos, Enugu, Nasarawa, and Gombe states in September and October 2020. The 10,000 were representative of the population in the states, it said.
The survey found that the prevalence of Sars-CoV-2 antibodies was 23% in both Lagos and Enugu, 19% in Nasarawa and 9% in Gombe.
“This means that as many as 1 in 5 individuals in Lagos, Enugu and Nasarawa state would have ever been infected with SARS-CoV-2. In Gombe, the proportion is about 1 in 10,” the researchers said.
A second phase of the survey was done in Kano state and the federal capital territory of Abuja in 2021. Its results have not yet been published.
The findings of the study discussed in the Guardian’s analysis do not support the paper’s claim.
Another study hints at 50% antibody prevalence
Other researchers have tried to estimate the extent of infection in the country. One is Oyewale Tomori, a professor of virology and former president of the Nigerian Academy of Science. He told Africa Check he was involved in a seroprevalence survey of 12 states.
This found that all of Nigeria had a Sars-CoV-2 antibody prevalence of over 50%, Tomori said. But he could not give any more details as the study had not been published.
"That you have developed antibodies does not mean you will always be protected from the virus.”
We do not have data that supports the paper’s estimate of 50%. But even if this share were accurate, does it mean that half of Nigerians have survived Covid-19, as the Guardian asserted?
This was accurate, Mirabeau Tatfeng, a professor of medical microbiology and immunology at Niger Delta University, told Africa Check.
“The presence of antibodies is evidence that the person was exposed to the virus and if the person didn’t die, it means they survived it, whether the person was ill or asymptomatic,” Tatfeng said.
He said NCDC records for example indicated a survival rate of over 80%, with about 3,000 deaths from 250,000 cases. Studies have shown that many cases were not reported, and that testing was low in Nigeria, with only 5 million samples tested for an estimated population of 216 million.
But Tatfeng added that many studies had not included children, so their results might not apply to all Nigerians.
Interpreted directly, this claim by the Guardian is correct.
All the experts did however warn that the presence of antibodies didn’t mean a person couldn’t be infected in the future.
Antibodies ‘wane over time’, don’t guarantee protection
“Only those who were down with Covid-19 to the extent of getting hospitalised would develop strong antibodies,” Tomori said. “But then antibodies wane over time. That you have developed antibodies does not mean you will always be protected from the virus.”
But a high level of antibodies could reduce the severity of infection.
Also, most of the people exposed in Nigeria were asymptomatic, professor of public health Tanimola Akande told Africa Check. In an April 2022 statement the WHO said this was the picture across Africa.
The antibody levels of asymptomatic patients “may not be high enough to prevent infection among them”, Akande said. “It is therefore important for people to take the necessary doses of vaccination.”
Tomori added that the prevalence of antibodies should not be interpreted as herd immunity in Nigeria as this was “complicated”.
Herd immunity is the indirect protection from an infectious disease when a population is immune either through vaccination or immunity developed from previous infection.