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Do we need to take multiple vaccine doses before 2024?

January 05, 2021 09:23 IST

With the virus mutating, can vaccines be assumed safe and effective in the long run? asks Atanu Biswas.

IMAGE: A COVID-19 vaccine administration dry run at a health care centre in Bhubaneswar, Odisha, January 2, 2020. Photograph: Sarangadhara Bishnoi/ANI Photo

With a new strain of coronavirus causing a surge in COVID-19 infections in the UK, an important and immediate question is whether the vaccines that are being rolled out or are on the cards would work against the mutant.

The new variant is up to 70 per cent more transmissible than earlier strains, prompting several countries to ban flights from the UK.

Although there is no evidence yet to suggest that the vaccines will be less effective against the new strain, the concern will linger until more data on this issue is available.

Certainly, more such contagious mutants may emerge in the near future, and that would weigh on the efficacy of vaccines.

While developing a vaccine usually takes at least a few years, and often decades, if at all, several Covid vaccines are ready within a year of the outbreak.

The pandemic provided a rare opportunity to the pharmaceutical industry to grab some share of the potential global vaccine market worth billions of dollars, and they worked with full vigour to capitalise on this situation.

However, can the vaccines really become the 'magic dust' for humanity's effort to bring the world back to normalcy?

For questions about the vaccines' long-term safety and efficacy persist.

Ever since the quest for Covid vaccines began, safety was a serious concern.

In March, Nature published an article entitled 'Don't rush to deploy COVID-19 vaccines and drugs without sufficient safety guarantees'.

Still, the world witnessed an unprecedented rush.

There is no denying that, in a desperate bid to restore normalcy around the world, rapid development of an efficacious vaccine was urgently needed.

And the pharma industry did its best in this rescue bid.

But, the 'safety' and 'efficacy' of the vaccines are bound to be observed over only a very short duration in the development stages of such accelerated vaccine rollout.

And, hence, possibly nobody knows about the long-term behaviour of the vaccines.

Vaccines are usually approved on the basis of results from three stages of clinical trials.

The trials aim at assessing short-term safety, ability to generate an immune response, and efficacy.

Although most adverse events occur shortly after receiving a vaccine, safety issues, including occurrences of possible rare side-effects, should be monitored long enough thereafter, specially if the vaccines are developed in unusual hastiness.

Most of the Covid vaccines have high observed efficacy values -- between 70 per cent and 95 per cent.

An 80 per cent efficacy, for example, means (100-80) = 20 per cent risk ratio, the ratio of case rate of vaccine to that of placebo among the volunteers.

No significant safety concerns have been reported for most vaccines in the trial stage.

That sounds good.

So, can such vaccines be then assumed safe and effective in the long run?

Unfortunately, nobody knows at this point in time.

The race to develop a vaccine is so competitive and society's demand so enormous that success stories of the vaccines are announced even without adequate knowledge of their long-term safety.

Quite naturally, after such a dramatically compressed schedule of development and approval, the vaccine-makers are asking governments to indemnify manufacturers against lawsuits.

And they'd possibly be granted such protection in many countries.

COVID-19 vaccination in India may start in January, and some experts believe that normal life may return by September-October.

If that happens, that would simply be great.

However, it is not yet clear how long the vaccine would be able to resist the disease.

Do we need to be vaccinated periodically, as in the case of flu?

If so, how often will that be?

A continual assessment of long-term safety along with estimates of waning time of antibodies generated by vaccination is possibly needed.

And, understandably, safety and effectiveness would vary from stratum to stratum even within the same population.

With a lot of questions being unanswered yet, many people would have to make a judgement call on vaccination depending on their health conditions, age, and medical history, as comprehensive guidelines are difficult at this early stage.

This will be a general problem worldwide.

Although the hasty development of Covid vaccines was possibly a compulsion during the pandemic, we possibly need to administer the recipients with utmost care and also follow up the vaccinated persons diligently -- which is never an easy task by any standard.

Building the necessary infrastructure, including adequate cold chain points, and the cost of vaccination are important factors to consider in mass vaccination.

As experts perceive, it will be 2024 till everybody in India, if willing to take a vaccine, can be vaccinated and protected.

But, many people believe that the immunity obtained by vaccines might not last beyond a few months.

If that happens, do we need to take multiple vaccine doses before 2024?

Even then, many are hoping that the disease chain could be broken by immunising a sufficient number of people at a time.

And if, for example, the vaccine works for only six months, it might not be practical to vaccinate more than 15-20 per cent of the country over a six-month period.

In that case, it might not be easy to achieve 'herd immunity' by immunising about two-thirds of the population at a time.

A lot of unanswered questions would keep haunting us for another few months or even more than a year, with fingers crossed and masks on, of course.

Atanu Biswas is professor of statistics, Indian Statistical Institute, Kolkata.

Feature Presentation: Ashish Narsale/


Atanu Biswas
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