Antibodies against coronavirus, produced by the immune system as a result of vaccination, wane over time. Recent studies have suggested, however, that this process may be happening at different rates for different COVID-19 mRNA vaccines. Scientists are wondering what this means for immunity to COVID-19 and how it relates to the administration of any subsequent doses.
Hopes were high when the results of the third phase of clinical trials of two SARS-CoV-2 mRNA-based vaccines – one developed by the US-German Pfizer/BioNTech consortium and the other by the American Moderna – were published in late 2020.
Both vaccines were found to be more than 95 per cent effective at preventing COVID-19. None of the other types of COVID-19 vaccines, those including inactivated virus or virtual vector-based, proved to be this effective.
Recent studies have shown, however, that antibody levels decline in older age groups. This was confirmed by the observation of the participants in the Pfizer tests, which continued to be carried out after the end of clinical trials.
COVID-19 antibodies fade more quickly in elderly people
According to the findings of researchers from Case Western Reserve University in Cleveland, Ohio, who examined 120 nursing home residents with a median age of 76, older people not only lose antibodies faster, but may also produce less antibodies from the outset.
Much younger home care staff served as a comparison group, and received vaccination at the same time as older patients. Not only did they maintain high levels of their antibodies longer, but they also produced more of them right away.
As a result, 16 per cent of nursing home patients who had never been exposed to the coronavirus before, had antibody levels below detection two weeks after receiving the second dose of Covid jab.
After six months, a serious decline in antibody levels was observed in 70 per cent of the patients, but only in 16 per cent of their caregivers. In both groups, however, there were significantly fewer coronavirus-related infections, illnesses or deaths than among unvaccinated people.
The study was conducted on a very small group of people and therefore its results cannot be taken for granted, but a team leader from Cleveland, Dr. David Canaday, explains that it is worth a closer look as it could help identify which age groups should already be vaccinated booster doses, and which can wait or even don’t need them at all.
High level of antibodies isn’t the most important thing
Scientists are still studying how the human immune system works, but it has long been known that antibodies are not its only component. Those produced by vaccination are rather part of the body’s „first line of defense”. The task of antibodies is to find the pathogen, attach to it, mark it and destroy it.
But some scientists doubt that antibodies (so-called humoral immunity) are the most important element of our immune response, especially when viewed in the long term. The so-called immune memory, which allows our body to learn to fight the pathogen efficiently when needed, may be more crucial.
Vaccinations are also fundamental here, because they train our body and teach our T lymphocytes (part of the so-called cellular immunity) to fight pathogens, to recognise the threat and react faster before the virus multiplies in our body. And in the case of B lymphocytes – to produce new antibodies that may also be effective against new variants of a given virus.
However, the level of such immunity is difficult to measure in laboratory conditions (because it works best in a real „fight” with an infection), so the most common method is to compare the number of antibodies. It is simple and seems to give a clear answer, although there are doubts whether the result is completely reliable.
That said, more and more scientists are of the opinion that the idea is not to keep antibody levels high, but to train the body to produce them quickly when needed.
Moderna presents more antibodies than Pfizer / BioNTech?
This is why scientists are cautious about the results of another study, which was carried out in Belgium. They analysed the level of antibodies in 1600 employees of the large Oost-Limburg hospital complex in the city of Genk.
It turned out that in the period from 6 to 10 weeks after receiving the second dose, people vaccinated with Moderna had on average 50 per cent more antibodies than those vaccinated with Pfizer / BioNTech. The relationship was visible between each of the age groups.
Researchers from the American University of Virginia also drew similar conclusions, but based them on the analysis of only 167 cases of people vaccinated with mRNA vaccines.
But again, in both Belgium and the US, it did not make a significant difference in the number of infections or hospitalizations among the vaccinated. It remained significantly lower than in unvaccinated people. According to Dr. Canaday, „waning of antibodies does not mean that there is no protection against the coronavirus.”
For now, it is not known why the Moderna vaccine, very similar to the Pfizer / BioNTech one, is expected to cause greater production of antibodies in the vaccinated person. However, there are hypotheses that this may be because Moderna put more doses of its COVID-19 vaccine in each vial or that the manufacturer’s recommended interval between doses to be slightly longer.
Concerns over the Delta variant
Scientists are concerned, however, that in the case of emergence of new variants of the coronavirus – especially the Delta variant – the effectiveness of vaccines (not only the mRNA ones) decreases slightly, although it still remains at a high – probably around 80-85 per cent – level.
However, with this strain of the pathogen, there are clearly more cases in which fully vaccinated individuals develop symptoms of COVID-19 than with earlier strains. Hence the debate in the Western world over the issue of administering a third dose of the vaccine.
Israel has been doing this since the beginning of August, where now all adults can take a booster dose, and in some European countries (including Poland), groups at the highest risk – the elderly or people with immunodeficiency (e.g. due to cancer treatment).
On September 17, the federal Food and Drug Administration (FDA) issued its recommendation on administering a third dose of the vaccine in the US. A group of scientific advisors to this institution, as well as a group of advisers to the most important American epidemiological agency – Disease Control Centers (CDC) – have published a joint position on this issue in the medical magazine „The Lancet”.
It indicated that „the average person does not yet need a booster dose of the vaccine,” and it should only be given to people whose immune systems are weaker.
Vaccination of the unvaccinated more important than the third dose
It was also emphasized that the unvaccinated people are still by far the most important vector of transmission of coronavirus infections, and this is the case even in populations with high vaccination rates.
„The currently available studies do not provide reliable evidence of a significant decrease in protection against severe disease, which is the primary goal of vaccination,” said one of the authors of the paper, Dr. Ana Maria Henao Restrepo.
According to the group of experts, the authorities should therefore focus on getting as many people as possible to receive the first and second doses of the vaccine, because unvaccinated people are 4.5 times more likely to become infected, and they are at a 10 times greater risk of hospitalization and 11 times greater risk of dying from COVID-19.
The World Health Organization (WHO) is, however, calling for a third dose moratorium in the richest countries in the world to give a chance to buy vaccines for poorer countries where few people have received a COVID-19 immunization.
For example, as John Nkengasong, director of the African Center for Disease Control, informed on 14th September at a conference in Geneva, so far less than 3.5% of the 1.5 billion people in Africa are vaccinated against COVID-19.