- Herd immunity is achieved when more than 70 per cent of the population develops protection against the disease either through vaccination or infection.
- This makes it difficult for the disease to spread anymore in the community.
Image: GERALD MUTETHIA
Kenya achieved herd immunity for Covid-19 early last year, despite the low levels of vaccination, according to experts.
Herd immunity is achieved when more than 70 per cent of the population develops protection against the disease either through vaccination or infection.
This makes it difficult for the disease to spread anymore in the community.
Acting director general for Health Patrick Amoth and several other researchers said Kenya achieved herd immunity mainly through natural infections because few people are fully vaccinated against the disease.
“Despite vaccine inequity, hesitancy and refusal, herd immunity had been achieved in Kenya and likely other African countries by early 2022, with natural infections likely contributing to most of this immunity,” they said.
But this does not mean people should stop taking Covid-19 vaccines, they said.
“Vaccine campaigns should be sustained due to the need for repeat boosters associated with the waning of SARS-CoV-2 immunity and emergence of immune-evading virus variants,” they said.
The other researchers are from the Kenya Medical Research Institute, Washington State University Kenya programme, US’s Emory University, KAVI-Institute for Clinical Research and Nairobi and Kakamega county governments.
They tested 1,565 participants for SARS-CoV-2 antibodies in Nairobi and Kakamega counties in January and February 2022.
They found that nearly everyone in Nairobi had Covid-19 antibodies.
This was despite low levels (less than 55 per cent) of vaccine uptake nationally and high levels (16–20 per cent) of vaccine refusal among the two populations.
“Widespread SARS-CoV-2 transmission across all communities in the country is the most plausible explanation for this herd immunity, an argument supported by the findings of significantly higher seroprevalence in urban (97.8 per cent) than rural (85.9 per cent) populations,” they said.
Their findings were reported last week in the Vaccines journal, under the title 'Near-Complete SARS-CoV-2 Seroprevalence among Rural and Urban Kenyans despite Significant Vaccine Hesitancy and Refusal.'
Scientists projected that at least 70 per cent of the population needed to be immunised against SARS-CoV-2 to achieve the herd immunity needed to break virus transmission.
The World Health Organisation had warned against herd immunity through natural infection several times because it could lead to many deaths.
However, rich countries hoarded vaccine supplies in 2021 and developing countries such as Kenya were unable to secure sufficient doses.
According to Health CS Susan Nakhumicha, 5,688 people in Kenya have been killed by the disease since 2020 but no deaths have been reported since December last year.
“Cumulative deaths by age remain: 0-9 years (62), 10-19 years (44), 20-29 (152), 30-39 years (415), 40-49 years (654), 50-59 years (1,034), 60 years and above (3,327),” Nakhumicha said.
Dr Amoth’s team said up to 20 per cent of the eligible Kenyans still refuse to take the Covid-19 vaccine, which are now easily available.
While this proportion was not large enough to prevent the achievement of herd immunity, it may create pockets of SARS-CoV-2 transmission and lead to deaths in the future.
They said due to the rapidly waning SARS-CoV-2 immunity and emergence of immune-evading virus variants, vaccine campaigns with upgraded vaccines should be sustained globally.
Last week, WHO said combined protection from Covid-19 vaccines and natural infection protects for one year, after which it wanes rapidly.
This protection, called hybrid immunity, comes after the most recent infection of full vaccination, in any order.
The health agency said such a person has 95 per cent protection against hospitalisation and severe disease.
However, this protection falls to 42 per cent after the first year, WHO said in an analysis published in The Lancet Infectious Diseases last week.
For those with previous infection and no vaccinations, effectiveness against hospitalisation and severe disease was nearly 75 per cent for one a year, while protection against infection was less than 25 per cent.
“Protection from previous infection should not detract from the need for vaccination,” the Lancet analysis said.
“Furthermore, there are serious risks associated with infection. These include the risks of hospital admission, ICU admission and mechanical ventilation, and death.”
The WHO analysis comes two yeas after the first vaccine was authorised globally.