COVID-19 vaccine efficacy is waning. Is it time for the third shot?

At a time when the vaccination drive in India has picked up pace, reports about declining vaccine efficacy has proved to be a dampener. Recent data suggests the effectiveness of COVID-19 vaccines is on the wane. This has led to debates over whether it is time for a booster dose.

A study published in US Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report said post-COVID-19 vaccine immunity seems to be declining. The US authorities authorised booster jabs for all Americans from 20 September starting eight months after a person has been fully vaccinated.

An Israel based study showed that people vaccinated in early January are more vulnerable to contracting the COVID-19 virus, as compared to the ones vaccinated later. Researchers at the University of Oxford, UK, and the country’s Office for National Statistics analysed a vast data set and arrived at the conclusion that Pfizer–BioNTech and Oxford–AstraZeneca COVID-19 vaccines are effective against the highly infectious Delta variant of SARS-CoV-2 — but their protection drops away over time.

What, however, comes as a relief is that data suggests while the protection against incurring the infection has declined over time, the protection against hospitalisation remains high.

Put simply, this means that while even vaccinated people are increasingly at risk of contracting the virus after a period of time, they are unlikely to land in hospital with severe COVID illness.

Why efficacy is waning

The US Centers for Disease Control and Prevention in its report said that the effectiveness of COVID-19 vaccines among frontline workers declined to 66 per cent after the delta variant became dominant, compared with 91 per cent before it arose. 

“Although these interim findings suggest a moderate reduction in the effectiveness of COVID-19 vaccines in preventing infection, the sustained two-thirds reduction in infection risk underscores the continued importance and benefits of Covid-19 vaccination,” researchers wrote in the agency’s Morbidity and Mortality Weekly Report.

It needs to be remembered that the vaccine is still based on the original ‘Wuhan strain’, the longer-term effectiveness is one concern. 

The UK study also shows that vaccinated people who become infected with the delta variant carry high peak levels of virus. When the alpha variant was dominant in the United Kingdom, vaccinated people who became infected had lower peak viral loads. The findings suggest that both vaccines are effective against delta after two doses, but that the protection they offer wanes with time.

Is it time for the third jab?

The World Health Organisation (WHO) has said, as per the current data, that coronavirus booster shots are not needed. WHO chief scientist Soumya Swaminathan, asked about the need for boosters to increase protection against the disease, told a Geneva news conference: “We believe clearly that the data today does not indicate that boosters are needed.”

Since it is now proven that no vaccine provides full protection against infection/reinfection, a third jab too is unlikely to do it. This means even the efficacy of a third dose will wane. Data still shows improvement in antibody levels after a third dose. So, some countries are considering a third dose nevertheless.

As the global debate on booster jabs heats up, several scientists in India said the priority must be to ensure that more people are inoculated with at least the first jab. In India, large number of people are not yet fully vaccinated and the priority is thus to protect those susceptible to hospitalisation with two doses.  

A recent study by Indian Council of Medical Research-regional medical research centre (RMRC), Bhubaneswar, found the level of antibodies produced among Covaxin recipients starts to decline after two months. The study said the same for those vaccinated with Covishield starts after three months. 

Immunologist Satyajit Rath said less than 15 per cent of the country’s adults have been vaccinated with both doses, and this means that all Indians who are more vulnerable to infection have not yet necessarily gotten two doses.

Rath added that while antibody levels are indeed going down after a few months, this is neither surprising nor does it necessarily indicate any substantial loss of protection. How much longer it will be before any such loss begins to be seen is an empirical question and we will have to wait for data, the scientist added.

Meanwhile, Immunologist Vineeta Bal said India should not think of providing booster doses at this stage when about 40 per cent of the eligible population is yet to receive the first dose. 

Soumya Swaminathan has called for more research to ascertain if a third dose should be part of the public health policy against COVID-19.