Study offers clues to why COVID-19 vaccine protection wanes quickly

Context: Recently,
the authors reviewed 34 licensed vaccines for the duration of protection
against different infectious diseases. Only five offer long-lasting protection.
The ideal vaccine offers nearly complete protection against infection and mild
disease in just one dose. It is simple to administer and doesn’t have any
adverse effects. The protective immunity lasts a lifetime. In practical
scenarios, no single vaccine provides such advantages. The key challenges
vaccine developers face is the vaccines’ durability, the lack of immune
correlates of protection, and the inability to protect against infection and
transmission. But the greatest challenge among these three bottlenecks is the
inability of vaccines to confer long-lasting protection.

Key
points

·       Overview: The future
of vaccines protecting against challenging or emerging infectious diseases lies
in the design of new immunogens, their release mechanisms, and the mechanisms
of action of various adjuvants.

·       India’s
Vaccination Strategy: Phased approach- The drive began with
healthcare and frontline workers, followed by those above 60 years, and then
those above 45 years with co-morbidities.

AEFI
(Adverse Event Following Immunization) monitoring- A
surveillance system to monitor and address any side effects or adverse
reactions post-vaccination.

Equitable
distribution- Ensuring that vaccines reach every state and union territory in
proportion to their population and the number of cases.

Continuous
review and feedback loop- Regular reviews of the vaccination strategy to
address any challenges and feedback from the ground level.

Diversified
Vaccine portfolio- Granting emergency use authorization to multiple
vaccines to ensure a broad supply.

·       Vaccines
and lasting protection: The immunity that follows an infection — natural or
vaccine-induced — is mainly the result of the body generating antibodies. A
specific type of immune cell known as a plasma cell, which comes from B-cells
in the lymph nodes, secretes these antibodies.

Long-lasting
plasma cells (LLPCs)- Some plasma cells, known as long-lasting plasma
cells (LLPCs), also migrate to the bone marrow and survive for an extended
duration, promoting the production of antibodies in this time. A vaccine’s
ability to confer long-term protection thus depends on its ability to induce
the production of LLPCs. The goal of all vaccine developers is for their
vaccines to generate these cells in the bone marrow.

·       New
evidence on LLPCs: Researchers studied the presence of different subsets
of antibody-secreting cells (ASCs): LLPCs and short-lived ASCs (which
include non-LLPCs) in the bone marrows of 19 healthy volunteers aged 20-65
years, within 2.5-33months of receiving a COVID-19 mRNA shot. The results
concluded that LLPCs are responsible for durable immunity. Their absence in the
bone marrow is responsible for the rapid waning of both vaccine- and
infection-induced protection against COVID-19. The results were similar for
ASCs secreting different immunoglobulins (IgG and IgA).

·       Repercussions
with the COVID 19 vaccine: The most popular COVID-19 vaccines
during the pandemic were mRNA vaccines. Some other vaccines, including that
against the human papillomavirus, utilise the virus-like particle (VLP)
platform. Here, the vaccine presents the virus’s spikes more effectively to the
body’s cells, facilitating better BCR cross-linking. Thus, the distance between
spike proteins on the surface of SARS-CoV-2 viral particles may prevent the
production of LLPCs after an infection or a vaccine dose. This could then
explain why the protection conferred by COVID-19 vaccines, whose effect is
based on the spike proteins, wanes rapidly.