Understanding the science of Covid-19 vaccines booster shots

Vaccines remain an extremely effective weapon at hand at preventing severe Covid-19 infection and death.

As Kenya struggles to vaccinate at least 10 million people before the end of 2021, the debate on administering booster doses rages on.

With the Omicron variant rapidly spreading across the world less than two months after it was first isolated by scientists in South Africa, most countries including Kenya are considering the possibility of a booster vaccine dose.

The US CDC has recommended an extra shot for the elderly and those with a compromised immune system as well as those aged 18 years and above with existing medical conditions and those in high-risk jobs such as healthcare workers.

A Covid-19 booster shot is an additional dose of a vaccine given after the protection provided by the original shot(s) has begun to naturally decrease over time.

A booster tricks the immune system into thinking that it is again seeing a pathogen, so antibody-producing cells, and other immune cells, are recalled into gear.

According to an assistant professor at Harvard Medical School Jonathan Abraham, because of highly transmissible variants, there will be need for periodic boosters for the next few years.

During that time frame, using an updated vaccine strain may be wise because we are unlikely to ever see the original vaccine strain again as it has virtually gone extinct, he said.

“For now, the same SARS-CoV-2 spike protein antigen is used for the vaccine and the boosters. However, there is the chance that, over time, it will shape-shift or mutate enough that a booster with an updated strain antigen would be required to prime the immune system to recognize the mutant virus,” Abraham said.

The ministry has been gathering local data on the need to administer Covid-19 booster jabs to those already fully vaccinated.

Vaccines deployment taskforce chair Willis Akhwale had hinted at a possibility of administering the booster annually should evidence suggest so.

“Booster means somebody was already fully protected to be boosted. This is what is being monitored with a possibility that this may become an annual requirement if at the end of the 10 months since people got vaccinated the levels will be low,” Akhwale said.

IMMUNE RESPONSE

Experts argue that even though it is not possible to tell when your booster becomes fully effective, it is unlikely you will have extra protection the day after you get your booster because it usually takes days or weeks for the memory cells to produce more antigens.

Previous studies have shown that once you are injected with the vaccine, it takes three weeks for your body to mount an immune response.

A senior Infectious disease expert at the Johns Hopkins Center for Health Security Amesh Adalja noted that most people will experience some positive effects from the booster within a week, but the full effect is believed to kick in two weeks after the booster.

"In general, that's how the immune system responds and how long it takes to arrive at the peak level of protection," he was quoted by the Science.com website.

According to global health expert Dr Bernard Muia, the only weapon so far against Covid-19 is vaccination and observing the existing containment measures.

On Tuesday, the technical advisory committee on vaccination held a meeting to discuss among other issues the possibility of administering a booster dose and the vaccine mixing and matching schedule after the World Health Organisation on Friday issued interim guidelines on the same.

“What that committee is going to look at is number one should we have booster doses and the way we will be going around mixing. The main issue of mixing of vaccines, from the programme perspective,” Dr Richard Ayah told the Star.

“It is much better if it is done from the programme perspective if the committee thinks there should be booster doses, then it looks like the vaccine should be mixed, you don’t get the same vaccine you got for the first two doses,” he noted.

Edited by D Tarus