Fourth dose warning – Covid boosters don't spell end of pandemic struggle

David Katz, emeritus professor of immunopathology at UCL, said that we simply “don’t know” whether a fourth jab will be necessary to provide adequate long-term protection from Covid and further strains of the virus. However, failing to immunise the developing world – where COVID-19 vaccines are scarce, providing a breeding ground for new mutants – could mean we will not see the back of the pandemic for a few years to come.

It comes amid the UK Health Security Agency advising that a fourth dose of the vaccine is not necessary, as data shows that three months after a third, booster jab, protection against hospitalisation remains at about 90 percent for those aged 65 and over.

Professor Katz commented: “I think fourth doses are harmless. By and large, there aren’t adverse reactions to fourth doses.

“The thing is, we use three doses for Covid, we use three doses for MMR [Measles, Mumps and Rubella], we use three doses for DTP [Diphtheria, Tetanus and Pertussis]. We use three doses in quite a number of conditions, and the I don’t see I can’t do any harm and may help protect.”

However, he noted: “It’s very early days to know whether immunisation with RNA-based vaccines like Pfizer and Moderna has a less prolonged half-life than other forms of vaccination. We don’t know the answer to those questions yet.

READ MORE: Why there shouldn’t be a fourth Covid vaccine – experts weigh in

“And that’s what we need to know. We can say fourth vaccines are necessary, [but] that takes time.”

Professor Katz added: “Would have a fourth dose myself, personally? Yeah, why not? I believe in vaccination. And if there’s any evidence this one might wane a bit? Good idea.

“That’s if you’re asking me personally. If you’re asking on a population basis, it’s just not quite as straightforward. There is something about giving people a fourth dose which there [is] this kind of distaste.”

He told that talk of the need for further Covid vaccines did make the immunisation process seem “endless”, but noted: “we accept flu vaccines which are endless”.

An article in the Journal of Medical Ethics, published in October 2021, argued in favour of the World Health Organisation’s (WHO) call to forego booster shots until 10 percent of everyone in all countries was fully vaccinated, as not helping other nations during a pandemic “will prolong the pandemic, harming everyone, including their own citizens”.

Many of the least developed countries have barely administered first doses of the COVID-19 vaccine. As of January 10, in the Democratic Republic of Congo, Haiti and Chad, just 0.3, 1.1 and 1.7 percent of the population had received a first dose respectively.

In October, Dr Bruce Aylward, senior leader at the WHO, warned that the coronavirus pandemic could “easily drag on deep into 2022” due to low vaccination rates in impoverished countries.

He added that the pandemic would “go on for a year longer than it needs to” because poorer countries were not able to access the vaccines they need.

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When asked whether the Omicron variant was a symptom of the disparity between vaccination rates in the first and third world and whether we may be locked in a vicious cycle of variants and boosters until they are immunised,

Professor Katz responded: “Yes, that’s exactly the risk.

“Now whether that takes 2022, or a couple of years to pan out is another matter, because who knows. You couldn’t predict how quickly that will happen. But it is a real, real concern.”

Fourth doses had been mooted as immunity thanks to the vaccine had been shown to wane in studies.

Professor Katz speculated that “part of the reason why they may be a drop off with the vaccine is that we are measuring antibodies as part of our readout, and we aren’t measuring the T-cell response.

“So you may have no antibodies, but you may have a perfectly good T-cell response that kicks in. The efficacy of the vaccine might not be measured as accurately as it is; it maybe more efficacious than we think it is.

“But conversely, it may be that we’re measuring the antibody response, and there isn’t a T-cell response, and therefore, it isn’t working as well as it should.”

There are two types of T-cell response: one that makes antibodies and another which kills the infected cells. Professor Katz said: “You need both of those responses, and you need memory.”

He explained that there had yet to be a “really good test” of the T-cell response to coronavirus, adding: “I’d be so much happier about the vaccine if they if they were able to show that there is a T-cell responses as opposed to an antibody response. And that even in some of the immunosuppressed, there may be a T-cell response.

“Now, it’s difficult to do that, because that’s the reason why it’s not been done. The reason why it’s not been done is the T-cells may not be circulating; they may be in the tissue, so you can’t get at them.”

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