Covid-19 herd immunity: Which way for Kenya?

To achieve protection against Covid-19, World Health Organization (WHO) chief scientist Soumya Swaminathan said 60 to 70 per cent of the population would have to be infected.

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What you need to know:

  • To achieve Covid-19 immunity, 60 to 70 per cent of the population would have to be infected
  • In Kenya this would mean between 28.6 million and 33.3 million people
  • If one per cent of these die, more than 285,000 lives would be lost
  • Some researchers have vehemently opposed the natural herd immunity approach

Test-and-trace programmes, new treatment, vaccines and more be damned, let us go for a different approach. These were the words of an international group of researchers to the world on how best to tackle Covid-19.

In the latest salvo in an ongoing battle of ideas on how to beat the pandemic, the experts signed the Great Barrington declaration, putting across arguments that have generated controversy.

Their argument was, now that it has been established the virus is unkind to the old and those with pre-existing conditions, we should do away with lockdowns and let the healthy face the virus until we all become immune.

Why not let the disease loose into the population, so that those who die, do and those who survive move on with life? They argued. The result would be herd immunity — when a virus is unable to spread because many people have been vaccinated against it or have survived an infection.

Without vaccine

To achieve protection against Covid-19, World Health Organization (WHO) chief scientist Soumya Swaminathan said 60 to 70 per cent of the population would have to be infected. This will break the chain of transmission because the coronavirus will not find new people to conquer and make sick. With no human host to live in, the disease fades out.

However, Dr Swaminathan said when the immunity is achieved without a vaccine, the human cost is too high, even if one per cent of the population dies.

Scientists who spoke to HealthyNation talked of a high price should we go the natural herd immunity way.

Omu Anzala, a professor and expert in viruses and the immune system, told HealthyNation that little knowledge about Sars-Cov-2 notwithstanding, six or seven in 10 people in the country would have to be infected for Kenyans to acquire herd immunity.

“Even if it was just one per cent of the population that would die in the process, have you calculated just how many people those would be?” he posed.

According to Kenya National Bureau of Statistics, the country has 47.6 million people from the 2019 census. If Kenya were to achieve herd immunity, between 28.6 million and 33.3 million people would have to be infected. One per cent of this would mean more than 285,000 dying.

Exposed to sickly mice

A team of researchers from the Kenya Medical Research Institute (Kemri)-Wellcome Trust programme estimated that the peak of Covid-19 infections, with the lockdowns and social distancing rules in place, was in July “with 34 – 41 per cent of residents infected”. Kemri had also projected that the infections would continue rising until this month.

Prof Anzala’s fear stems from the history of the term herd immunity, how it got its name and who would want to be the ‘herd’. In the 1920s, diseases such as cholera, dysentery, tuberculosis and typhoid fever roamed freely in the streets of England and left behind a trail of bodies. Two researchers from the University of Manchester — William Topley and Graham Wilson — started the diseases intentionally. The two would let sickly mice into one city, which would be exposed to a deadly bacteria, and another city would also be exposed, but its residents would get vaccines to protect them from the deadly viruses.

In 1923, the two scientists published their findings in a report to the Medical Research Council. In their paper, they said they counted the people who got sick, died, or survived. They demonstrated that protection against a disease in a population could slow an outbreak if we protect those who are vulnerable from future infections and deaths.

There is little encouragement in the places that tried to achieve herd immunity through natural infection. A paper that had not gone through peer review in the preprint medRxiv cites Manaus, a city in Brazil with a population of about two million people, where between 44 and 66 per cent of the city’s population was infected. The researchers estimated that between one in 500 and one in 800 residents died during this period.

It is understandable why some researchers have vehemently opposed the natural herd immunity approach. A total of 80 researchers from globally-acclaimed research institutions such as Oxford wrote an open letter to the journal Lancet, terming the idea that herd immunity without a vaccine would end the pandemic “a dangerous fallacy unsupported by scientific evidence”.

Misunderstood concept

WHO Director-General Tedros Ghebreyesus said in a virtual press briefing that allowing the coronavirus to spread in the hope of achieving herd immunity is unethical. “Herd immunity is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached,” he said.

Geoffrey Githinji, a researcher at Kemri-Wellcome Trust, who uses computer software to analyse biological and clinical data such as blood samples and DNA material, told HealthyNation most people championing herd immunity were referring to an often misunderstood public term,“herd immunity threshold”.

This number is derived from how many infections can arise from one infection, a pathogen’s basic reproduction number — termed the R-naught (R0). Each virus has a different number, affected by other factors such as nutrition and the general health of the population. The R0 of a highly infectious disease such as measles ranges between 12 and 18, meaning one person can infect another 18. This means to achieve immunity, 94 per cent of the population would have to be vaccinated or have survived the disease.

To achieve herd immunity and stem the growth of a disease, Dr Githinji said the RO would have to go below one. Dr Githinji pointed out the danger in relying on this number alone, without considering the environment the disease thrives in such as a country’s health capacity to handle the sick, immunisation and other public health interventions.

A disease like polio, which needs 85 per cent of the population to be vaccinated, has been eradicated in other parts of the world. WHO launched a polio eradication campaign in 1988, but even though the disease was kicked out in most of Africa, it remained endemic in west Africa. Polio hid in rural areas, festered in densely populated, unhygienic areas and would move to the places where children had been vaccinated. Even though the immunity is 18 years, children born would still be exposed.

The length of the Covid-19 vaccine immunity is still unknown, Dr Githinji said. “We still do not know whether the vaccine will be one that is given every few months or years,” he added.

On Friday last week, Dr Swaminathan announced that the earliest that healthy, young people could get the Covid-19 vaccine was 2022, and that priority was being given to health workers and those at highest risk.

Reinfection dilemma

She said while many vaccine trials were being undertaken, speedy, mass shots were unlikely and even for those who would be given first priority, the global agency needed to decide who were the most vulnerable.

Dr Githinji added that there had been concern about reinfection, and the science behind this was still unclear. “Is it reinfection? How long would your body take to clear the virus from your system to below detectable levels? If there is reinfection, do you have a different virus, so that we can say that you are immune to this and not the other?” he posed.

He called for more research, part of which is already going in Kenya, but has not yielded results.

In August, the Health ministry announced that it had launched a study to understand the long-term health effects of Covid-19. The research on 300 coronavirus survivors will be carried out in collaboration with researchers at the University of Nairobi, Kenyatta National Hospital, Mbagathi Hospital and Coast General Hospital.

“It will involve a thorough medical check-up of the patients through blood tests, X-rays, echocardiograms (heart images) and physical examinations,” Prof Anzala, one of the lead researchers, told HealthyNation.

Part of the study would involve interrogating how Kenyans from different parts of the country mounted immunity to the virus, depending on the environments they were in, and the pathogens they were exposed to.

There are studies in Kenya that have shown people’s immunities are suppressed by other factors such as exposure to aflatoxins in maize. In a study published in 2019, paediatrician David Githanga found that children in Makueni County, aged between six and 12 years, could not mount any response when vaccinated against Hepatitis B due to the high levels of aflatoxins in their bodies.


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