Covid vaccine protection lasts one year, WHO analysis shows

Covid-19 vaccines can now protect you for one year, but only after you have been infected with the virus, the World Health Organization says.

The year-long protection, called hybrid immunity, comes after the most recent infection of full vaccination, in any order.

The WHO 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 journal.

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.”

Last month, acting director general for health Patrick Amoth reported that Kenya achieved herd immunity for Covid-19 in February last year, because more than 70 per cent of the population has already been infected with Covid-19.

“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.

The WHO analysis also warned that people should continue taking Covid-19 vaccines.

“The analysis shows that hybrid immunity provides higher protection, demonstrating the advantages of vaccination even after people have had COVID-19,” WHO said in a statement.

The organisation said it might therefore be reasonable for individuals with a previous infection and full primary series vaccination to delay subsequent doses of vaccination by six months, while still maintaining high levels of protection against severe disease.

The declaration that Kenya reached herd immunity last year was made by Amoth and other researchers from the Kenya Medical Research Institute, Washington State University Kenya programme, US’ 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 month  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 WHO 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.

In Kenya, vaccination levels and testing for the disease are at an all-time low.

As of December 2022, the Ministry of Health had vaccinated 4.9 million pregnant and lactating mothers between 18 and 45 years.

According to government data, that accounts for only a third or 34 per cent of the number of women of reproductive age with complete Covid-19 doses.

The data shows that most of those vaccinated live in major cities and towns like Nairobi, Nakuru, Kiambu, Kakamega, Kisumu, Nyeri, Murang'a, Machakos and Bungoma.

However, the numbers in the North Eastern region are dismal with perceptions and attitudes still preventing people from taking vaccines.  

The ministry said that with the virus killing far fewer people, the public has moved to its pre-pandemic way.

“Health professionals have also evolved from taking care of sick people to prevention and encouraging communities to take on vaccinations,” 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,” the ministry said in its routine advisories on the disease. 

(Edited by V.Graham)