COVID-19 vaccines protect against serious illness but transmissibility can still continue and inoculated people can pass on the infection to others, say scientists, warning against complacency in those who stop maintaining protocol after they get their jabs. Transmissibility from vaccinated persons can be a risk factor until global coverage is achieved, top experts said as India’s Covid numbers escalated sharply, reaching 1,35,27,717 (1.35 crore/13,5 million) with 1,68,912 new cases on Monday to make it the country with the second highest number of cases after the US.
“Vaccination is simply one of the many different strategies we have to deal with in the pandemic. However, it is not a magical one-stop solution,” immunologist Satyajit Rath, from the New Delhi’s National Institute of Immunology, told PTI.
“None of the vaccines currently available provide protection against transmission of the virus. Statistically speaking, infection post-vaccination is likely to be milder than one without,” added Vineeta Bal, an immunologist from Pune's Indian Institute of Science, Education and Research.
As researchers around the world try and figure out how well COVID-19 vaccines prevent vaccinated people from transmitting the virus to others, the experts stressed on the need for masks and physical distance regardless of the vaccination status. This has to continue until the majority of people are vaccinated.
The scientists also batted for universal vaccination, saying it would provide strong community resistance to severe local outbreaks. Cautioning against lowering of the guard even after vaccination, they said some people who get inoculated early may lose their immunological memory over a period of time and become vulnerable again.
“Vaccination remains an individual protection, not a community protection, until we achieve almost global vaccination coverage. It is possible that vaccine-resistant virus variants will emerge, necessitating steady watchfulness and the rapid development-deployment of next-generation vaccines,” Rath said.
Bal agreed that disease severity will be low in vaccinated individuals as compared to those without vaccination.
“This is likely to be true even with variant viruses. Hence being vaccinated is a better state of affairs at a population level as well as individually,” Bal told PTI.
Rath noted that if an individual is effectively vaccinated, meaning they develop robust long-lasting levels of neutralising antibodies, then reinfection with vaccine-sensitive SARS-CoV-2 strains, even if it happens, is likely to be associated with only mild illness.
On the other hand, he said, a new infection with vaccine-resistant SARS-CoV-2 strains might still cause severe illness in some cases.
“So yes, vaccinated individuals could still pass on the infection, though the chance and the dose passed on would be lower. Of course, if they are infected with a future vaccine-resistant virus strain, then efficient transmission could occur,” he explained.
India’s vaccination drive rolled out on January 16 with healthcare workers (HCWs) getting inoculated. On February 2, vaccination of frontline workers (FLWs) started. . On March 1, the vaccination net was extended to those over 60 and for people aged 45 and above with specified co-morbidities. A month after that, on April 1, vaccination was opened for all people aged more than 45 years.
Amid demands from several quarters that the age limit for COVID-19 vaccination be relaxed in view of the spike in cases, the Centre last week said the aim is to protect those who are most vulnerable and not to "administer the vaccine to those who want it but to those who need it".
"The basic aim is to reduce death through vaccination. The other aim is to protect your healthcare system,” Union Health Secretary Rajesh Bhushan said during a weekly press conference.
He later clarified his remark, saying the government was following a dynamic supply-demand mapping model.
Last month, Union Health Minister Harsh Vardhan said "every vaccine doesn't require universal immunisation and all these priority groups whom we are vaccinating today like healthcare staff first and then senior citizens and people aged between 45 and 59 years, it will be extended in the coming days -- all these are based on experts' opinion”.
According to Rath, the idea behind this strategy is 'herd immunity', where the transmission cycle of the virus is broken if enough people are effectively vaccinated. And therefore even unvaccinated people no longer get infected, simply because the virus is no longer around.
“The trouble is that we don’t have a very reliable idea of what percentage of the community needs to be vaccinated for effective 'herd immunity' for SARS-CoV-2. So it is hard to see what use this government assertion is in practical terms,” he added.
The scientist explained that universal vaccination would be “nice” since it would provide very strong community resistance to severe local outbreaks.
Bal added that vaccinating almost everybody would be good in an ideal situation. However, robust safety data on pregnant women is not available for every vaccine and most vaccines are not tested on children below 12 years.
“Hence, the direct recommendation for these categories of people are hard to make. Though I feel vaccines made using older platforms such as killed vaccines or pure protein-based vaccines as against mRNA vaccines for example can be considered safe based on the experiences from the past,” she added.
Vaccines generate immunity by mimicking a milder form of an infection and helping the immune system "remember" the pathogen. So they contain some part of an infectious agent that is capable of generating an immune response, such as the viral genetic material, its RNA or DNA, or the proteins in the virus which interact with human cells.
If there are vaccine shots, and if it can be afforded, there is no harm in aiming for universal immunization, Bal said.
“Because by the time that level is achieved some people who got vaccinated early may lose their immunological memory and become vulnerable again. We do not know yet how long vaccine immunity will last for SARS-CoV2,” she added.
The two vaccines currently approved in India are Covishield, from the Oxford/AstraZeneca stable manufactured by Pune’s Serum Institute of India, and Covaxin, developed by Hyderabad-based Bharat Biotech in collaboration with the Indian Council of Medical Research and the National Institute of Virology (NIV).
On Monday, an expert panel of India's central drug authority recommended approval for Russia’s Sputnik V for emergency use with certain conditions.