COVID BOOSTER DOSE

 

Booster dose involve injecting people with an additional shot of the original vaccine and are required because, after a while, levels of circulating antibodies - immune proteins that can bind to the pathogens and block their ability to infect us - begin to wane, meaning immunity wears off. To prevent people becoming infected with the pathogen, this additional dose reminds their immune systems of what it looks like, boosting antibodies against it. For example, primary vaccination with three shots of the diphtheria, tetanus and pertussis (DTP) vaccine is given to infants to help build immunity against the bacteria responsible for these diseases, followed by three booster doses (containing the same inactivated bacterial toxins) during later childhood. For Covid-19, the situation is likely to be more similar to what happens with the seasonal flu vaccine. In this case, the adults and children receive a dose of a new vaccine each year because the influenza viruses mutate so quickly, rendering previous season’s vaccine almost obsolete. The immunity we get from a flu vaccination also wears off over time.

The good news is that, although new variants of SARS-CoV-2 are emerging, they appear to be developing similar “mutations of concern” independently of one another - ones which enhance the ability of the virus to bind to and infect human cells. This could suggest that SARS-CoV-2 is following a more predictable pattern of mutation than influenza. This, combined with the relatively slow mutation rate of the virus, could mean the vaccines may not have to be updated, and the population revaccinated, each year as it happens with flu, although that will also depend upon how long the immunity lasts and to what extent the virus continues to circulate.

In the case of Covid-19 vaccines, it remains unknown for how long immune protection lasts, but vaccine developers and health officials know it may not be forever - and that emerging variants may escape immunity. While the typical booster doses use the same vaccine that someone had previously received to remind the immune system about immunity to a pathogen, any future boosters for the Covid-19 shot could use different vaccines altogether. Currently, the need for and the timing for Covid-19 booster doses have not been established. No additional doses are recommended at this time.

In the battle for the booster shot, a vaccine manufacturer and the US government are drawing very different conclusions based on the evidence to date.

A US health official said the second dose for two-shot Covid-19 vaccine regimens was associated with higher rates of side effects, suggesting a third dose could potentially come with even greater risks, especially some of those more severe - although very rare - side effects.

Pfizer points to an encouraging data for a third shot to be given six months after initial vaccination in an ongoing trial of its Covid-19 vaccine. The Company said the study supports the vaccine efficacy against the Beta variant of concern first identified in South Africa.

Furthermore, a study published in a journal named Nature found two doses of the Pfizer vaccine produced strong neutralizing antibodies against the Delta variant in laboratory testing. The Company anticipates that a third dose will boost those antibody titers even higher.

Pfizer, along with its partner BioNTech, also pointed to an evidence that the existing two-dose mRNA vaccine regimen provides less protection against the current infections as the Delta variant continue to grow at an alarming rate worldwide.

The Thai Health Ministry recently said that more than 600 medical workers who received the two doses of the Sinovac vaccine have been infected with Covid-19, as the Thai authorities weigh giving booster doses to raise immunity. Of the 677,348 medical personnel who received two doses of Sinovac, 618 became infected, the data from April to July, 2021 showed. A nurse had died and another medical worker was in a critical condition. Both of them had underlying comorbidities. Most of the vaccinated frontliners who contracted the disease were able to avoid hospitalization and death. 

A Thai expert panel has recommended a third dose to trigger immunity for their medical workers who are at a higher risk. However, the panel is contemplating on administering a different vaccine; most likely AstraZeneca.

The above Thai data does indicate that vaccines are effective at preventing severe Covid-19 infections that would otherwise require hospital treatment. Consequently, mass vaccination will ease the workload and stress on our frontliners and at the same time, relieve the strain on our primary healthcare system.

As long as the virus continues to infect large numbers of people, the chances of it accruing additional mutations remains high, and this increases the likelihood that even updated vaccines may need replacing at some point. If this happens, it could warrant a shift away from vaccinating the entire population with the aim of stopping virus transmission, and prioritizing those most at risk of severe disease or death to maximize the impact of those vaccines instead.

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