COVID-19 Childhood Vaccines: Why Don’t They Last a Lifetime, Like the Measles Shot?
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The recent emergence of Omicron – a SARS-CoV-2 variant with suspected high transmissibility and infectivity rates – has prompted some of the world’s vaccination programs to be both expanded and accelerated. Not only will some countries now offer boosters to their already vaccinated older age groups, but they may also offer vaccinations to children.
While COVID-19 symptoms in children are usually mild, scientists remain concerned about the transmission of the disease, warning that children could represent a “virus shelter” – spreading potentially deadly variants amongst the unvaccinated.
The United States (US) Center for Disease Control (CDC) now recommends that all citizens aged five years and above receive a SARS-CoV-2 vaccine. With the Pfizer–BioNTech shot now approved for children aged 5-11 years old, millions more young Americans will be eligible for immunization. Similarly, an announcement is likely to be imminent from the United Kingdom (UK) Medicines and Healthcare Regulatory Agency (MHRA) on their decision whether to vaccinate children of the same age group. This vaccination program is expected to be rolled out in the new year, if approved.
Though the UK and US are moving ahead with plans for their childhood COVID-19 vaccination program, the issue remains hotly debated around the world. This polarization is in part driven by a risk-benefit assessment and the vaccines’ longevity.
Vaccines against different diseases vary in their longevity
In the developed world, many children receive a vaccine at some point in their young lives. Globally the proportion of routine childhood vaccinations is increasing. A reported 80% of US children are vaccinated against diphtheria, tetanus and pertussis (DTP), 90% against measles, mumps and rubella (MMR) and 92% against the now eradicated poliomyelitis virus (that causes Polio)* by 24 months of age. All of these shots offer long-lasting immunity, with the DTP vaccine lasting over five years and the MMR vaccine lasting a lifetime.
Phase III clinical trials have shown that the Pfizer–BioNTech vaccine is effective in children between the ages of 12-15 years old, offering seasonal protection against COVID-19. Vaccine-induced immunity is complex, and its duration is influenced by several factors. With scientists still working closely on the relationship between variants, vaccines and the immune response of children, it’s important to understand:
- Why do different vaccines vary so much in administration schedules?
- Why do COVID-19 vaccines appear to work seasonally?
- Why doesn’t childhood vaccination against COVID-19 offer a lifetime of immune protection, like some other childhood shots, such as the MMR vaccine?
Glycoproteins, the immune system and vaccination
The immune response to any virus, including SARS-CoV-2, is mediated by antibodies – specialized proteins produced within the body that recognize foreign invaders and signal for their clearance. Antibodies recognize molecules on the virus’ outer surface called glycoproteins. Humans are not born with the antibodies that recognize glycoproteins on the surface of SARS-CoV-2; therefore, adults and children alike develop their immunity though exposure or through vaccination. Vaccines trigger the production of antibodies without the risk of infection and represent the safest way to build childhood immunity to COVID-19.
While the immune systems of healthy children are generally some of the most efficient when it comes to fighting SARS-CoV-2, a recent study conducted at the Murdoch Children’s Research Institute (Australia) demonstrated that a lower proportion of children developed an antibody response to COVID-19 exposure when compared with adults. The findings, currently awaiting peer review, highlight the potential importance of childhood vaccination in building herd immunity and the pitfalls of reliance on naturally acquired immunity.
Why do measles vaccines last a lifetime when the COVID-19 vaccines do not?
The vaccination against measles is routinely administered in early childhood, typically between 9-12 months of age. While the early immunization and lifetime protection against COVID-19 is something the world may hope for, scientists recognize that key differences between the SARS-CoV-2 and measles viruses currently prevent this type of immune protection. “It comes down to the glycoproteins,” says Dr. Ben Bone, a virologist based at the University of East Anglia who specializes in vaccine technology and virus/host cell interactions. “In some viruses, such as influenza or SARS-CoV-2, the glycoproteins are more flexible and can handle more mutations while still functioning, resulting in a structural difference which affects their ability to evade vaccines.”
SARS-CoV-2, similarly to seasonal flu, can mutate from season to season. The mutations acquired over the course of several months can result in structural changes to its glycoproteins, making it unrecognizable to the antibodies produced in response to a previous vaccine. Hence, some medical professionals have suggested that a seasonal COVID-19 vaccine may be required every year.
The measles virus does not mutate in the same way as SARS-CoV-2. “Mutations [in the virus’ genetic material] may impair the glycoproteins on the measles virus’ surface, which it needs for entry into your cells,” says Bone. While the measles virus mutates as readily as any other similar virus, mutations in the antibody-binding glycoproteins are unfavorable to its infectivity. The mutated measles virus cannot cause infection and therefore no new vaccine development is required. Therefore, the vaccine is best administered in childhood, as it provides the best opportunity for a lifetime of immune protection.
What lessons can be learned from other childhood vaccination programs?
Like the influenza, human papillomavirus and DTP booster vaccine programs, the proposed vaccination of children in the UK against COVID-19 will be delivered by school age immunization services (SAIS) with oversight from the local National Health Service Trusts. In the US, the federal government is providing children with COVID-19 vaccines free of charge through their local pharmacies and healthcare providers. While the administration schedules of each vaccine program are tailored to its respective virus, there are key lessons that can be learned from the vaccination programmes of the past.
Much like the mass vaccination against rubella, the immunization of children against COVID-19 will have both direct and indirect benefits, protecting both the child and the vulnerable adults with whom they may come into contact. These benefits stretch beyond each individual’s health, protecting against the stress of parental illness and the socioeconomic effects of COVID-19 within families. Considering families and caregivers, the success of any childhood COVID-19 vaccination program centers around support from legal guardians. Clear, pediatric-focused clinical vaccine trials that can provide robust data will be required, to place each child’s caregiver at ease. The translation of clinical data into public health campaigns will also be essential to the programs’ success, as the fight against fake news continues alongside the fight against the COVID-19 pandemic.
*While the Polio virus does still exist, it was eradicated in the US and there have been no reported cases since 1979.