Could Covid herd immunity be achieved without vaccine?

MoH said blood serum study showed at least 1.6 million Kenyans exposed to virus by end of April

In Summary

• Health ministry confirmed reinfection has occurred but did not disclose numbers. Reinfection troubling, with worse cases reported globally.

• Not much is known about Covid immunity, how strong it can be, how long it lasts, and whether infection by one strain gives immunity against another. 

Scientists worldwide are trying to develop vaccines.
VACCINE: Scientists worldwide are trying to develop vaccines.
Image: FILE

As scientists urgently try to develop a Covid-19 vaccine, there is debate whether the virus should be allowed to spread naturally to achieve herd immunity.

WHO says that approach is highly unethical and precautions and interventions are necessary.

Allowing the virus to run its course is highly controversial, though it's well known that vaccinating a large number of people can achieve herd immunity for some diseases, such as measles.

Rising cases of Covid reinfection have raised questions about herd immunity.

The administration of US President Donald Trump was reported by the BBC to be considering herd immunity and natural progression of the disease to an outcry from scientists around the world.

Herd immunity occurs when a large portion of a community becomes immune to a disease through vaccinations or through the mass spread of a disease.

For this to be achieved, at least 70 per cent of the population would need to have virus antibodies.

On Tuesday, the Health ministry confirmed reinfection has been reported but did not disclose numbers.

“There have also been reported cases of reinfection ... so with respect to herd immunity still nothing is known about that,” Health CAS Rashid Aman said.

He added, “As we move along and we continue to generate more information, I am certain we will get a good feel for the epidemiology of this disease, the immunity that it evokes, how strong that immunity is, what type of immunity it is and how long it lasts.”

In June, the ministry said a study of blood serum confirmed at least 1.6 million Kenyans had been exposed to the virus by end of April.

This raised hopes that many Kenyans, especially in Nairobi and Mombasa, had gained immunity.

In 2018, scientists at the Kenya Medical Research Institute-Wellcome Trust Research Programme confirmed that people can catch the virus twice or even thrice.

Reinfection has been reported globally, some more serious than the initial cases, possibly indicating mutation of the virus. While known reinfection appears rare, the cases are worrying.

In a report published in the Lancet Infectious Diseases medical journal on Tuesday, a healthy 25-year old from Reno, Nevada, in the US tested positive twice to the virus.

The man with no clinical history of underlying medical conditions first tested positive to the virus on April, tested negative in two tests on May 9 and May 26 before testing positive again on June 5.

What is more concerning is that unlike the first infection, the second infection was more severe, with the man presenting with low blood oxygen and shortness of breath.

He was provided oxygen and went to an emergency department.

“Reinfection with SARS-CoV-2 has been reported in at least four individuals worldwide. Thus, previous exposure to SARS-CoV-2 does not necessarily translate to guaranteed total immunity,” the experts said.

“From a public health perspective, all individuals, whether previously diagnosed or not, must take identical precautions to prevent infection with SARS-CoV-2. Further work is needed to assess immune reactions in vitro after reinfection.”

On Tuesday, the World Health Organization advised against allowing Covid-19 to spread in the hope of attaining herd immunity, terming it "unethical".

WHO director general Tedros Ghebreyesus said herd immunity has never been used as a strategy for responding to an outbreak, let alone a pandemic like Covid-19.

“Herd immunity is achieved by protecting people from a virus, not by exposing them to it. Allowing a dangerous virus that we don’t fully understand to run free is simply unethical,” Ghebreyesus said.

For measles for instance, it is estimated that if 95 per cent of the population is vaccinated, the remaining five per cent will be protected from the spread of the virus.

Scientists say they need more research to understand how long immunity may last for people exposed to SARS-CoV-2, the virus that causes Covid-19, and how the prospect of reinfection could influence the hunt for a vaccine.

The CAS said  not much is known about immunity to Covid-19, adding containment measures have played a role in keeping the country where it is today.

 “These questions are still out there. Because of that and because of the possibility of reinfection, many countries that had in the beginning felt that they could ride this epidemic wave by allowing herd immunity to develop very soon realised that was not working and they had to go back and institute certain measures,” Rashid said.

He added, “We need to heighten adherence to those measures because that is one of the sure ways that we can prevent the transmission of the virus.”

(Edited by V. Graham)