ICMR cautions against “immune pressure on virus”: How vaccines can cause viruses to evolve
On Tuesday, India's foremost medical body, the Indian Council of Medical Research issued a warning that the careless use of therapies that haven't been fully understood to treat the COVID-19 infection could lead to unwanted immune pressure on the virus that may trigger mutations.
Drawing attention to how the current vaccines in development (or seeking approval) target the virus' spike protein, ICMR director general Balram Bhargava said, “we have to be very careful to look for any immunity breakthrough that may happen by vaccination.”
Vaccine science is confoundingly challenging but the underlying rationale behind it is fairly straightforward. Simply put, a vaccine exposes an individual's body to weakened or inactivated pathogens or small parts of them. This allows the immune system to generate immune cells, some of which produce antibody proteins capable of recognising the pathogen and staving it off if it invades again.
Most vaccines do not proffer lifelong immunity due to the natural evolutionary path of a virus. However, vaccine-induced evolution like what the ICMR director-general was referring to is different. In such cases, the reduction in the effectiveness of a vaccine against a pathogen is attributable to the vaccine itself.
The reason we haven't been able to develop perfect vaccines for
diseases like malaria, AIDS, influenza or trypanosomiasis is that these
microbes evolve too quickly. Immunity works when antibodies or immune
cells identify and attach themselves to specific parts of a pathogen.
However, if those parts of the pathogen were to mutate or change, the
virus itself may be able to escape or hide from a body's immune system.
The effectiveness of a vaccine depends on the number and variation of antibodies it stimulates. The greater the number and types, the more the lines of attack against the virus. Vaccines that only target a specific portion of the virus have a greater risk of becoming ineffective. As vaccine treatments continue to be administered, those strains that have managed to escape eradication soon become more prevalent in the world, effectively rendering the vaccine less and less effective over time. Essentially, the genetic profile of the virus or pathogen is fundamentally altered.
In fact, there is enough scientific literature to suggest that we have already witnessed this. A vaccine for hepatitis B, for instance, created antibodies targeting only a single section of one protein. While it turned out to be effective in the short-term, its efficacy fell remarkably over time. Another vaccine to stave off pertussis was also found to have driven resistance. It was able to fight the disease off but in targeting just a handful of proteins, it failed in effectively stopping infection and virus transmission.
Where we currently sit in our battle against COVID-19, we do not know exactly how the virus will mutate, how long the vaccines in development will proffer immunity for, or what effect the vaccines will have on virus transmissibility.
The recent discovery of a new and more aggressive strain in the
United Kingdom has caused alarm among several governments but experts
agree that further genomic sequencing is required before any conclusions
can be drawn over whether the vaccines developed may be relatively less
effective. One thing is clear though, the COVID-19 virus will continue
to mutate. How much of these mutations is down to vaccine-induced
resistance is a question time will ultimately answer.