A televised advertisement led to about 1,000 people volunteering at the All India Institute of Medical Sciences (AIIMS) to participate in human trials of the first vaccine being indigenously developed, signifying the beginning of a careful process to handpick participants for such studies that are pivotal in the future of the fight against the coronavirus disease (Covid-19) pandemic.

There are currently three Covid-19 vaccines at various stages of development in India. Prime Minister Narendra Modi said on August 15 that along with a plan for mass production, the road map for distribution of vaccines to every Indian was in place.

The three vaccine candidates approved for conducting various stages of human trials by the central drugs controller are Covaxin, developed by Bharat Biotech in collaboration with Indian Council of Medical Research (ICMR), Zydus Cadila’s ZyCoV-D and Oxford University and AstraZeneca’s vaccine.

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“We needed 100 volunteers but the phone number that we had advertised would not stop ringing. People were even sending requests through WhatsApp texts, which was apart from hundreds of emails that the hospital received from volunteers who wanted to participate in the trial. But we had to stop after a while because even after keeping extra numbers as buffer, the applications overshot the requirement,” said Dr Sanjay Rai, professor, community medicine department, AIIMS, Delhi. He is one of the principal investigators of the human trial of one of the vaccines.

Any healthy Indian adult can apply to participate in a Covid-19 vaccine clinical trial provided certain conditions are met. “The age group of the study participants is what is looked at first; the participants need to be ideally between 18 and 55 years of age. The next important criterion is that the prospective participants should not be suffering from any medical condition such as high blood pressure, diabetes, etc. They have to be absolutely healthy volunteers,” said Dr Rajnikant Srivastava, spokesperson, Indian Council of Medical Research (ICMR). ICMR is also supporting the Covid-19 vaccine projects.

There are many ways that can be used to publicise the enrolment process for trials, including advertising through print and electronic media, institutional or other websites, etc. Institutes that participate in the trials usually take a call on which medium to pick. “How these centres that are chosen to conduct the study select their study participants is purely their call to take. Normally, contact details are advertised through newspapers, television, websites, etc, but is decided locally,” said Dr Srivastava.

There is a window for the volunteers to apply. “Among the applications received, the selection is usually on first-come-first-served basis; like first 100 applications that fulfil the basic criteria will be short-listed, and invited, for the initial screening process. And if any of those fail, then others in the list are invited,” said Dr Rai.

Normally, about 25-30% applications are kept aside as buffer. Once basic screening is done, the participants are made to undergo a battery of tests that first begin with checking their Covid-19 status.

“A swab sample is taken to run a real time reverse transcription polymerase chain reaction (rRT-PCR) which is important to know whether they are infected or not. We have to look for participants who are neither currently infected nor have been infected in the past,” said Dr Rai.

Apart from nasopharyngeal swabs to run the rRT-PCR test, blood samples are also collected to check for possibly existing antibodies and other health statistics of trial participants.

“The blood test is to confirm whether the participant has antibodies against the virus in question as it would tell whether the volunteer has been infected at any point in the past without knowing it. For the trials, they need a participant who is not exposed to the virus in the first place, apart from them having to be free of any other disease. The tests are done for viral markers and blood parameters,” said Dr Navin Dang, owner, Dr Dangs Lab. His lab has been selected to conduct a part of the testing for one of the three vaccine trials.

The panel of blood tests for screening is to determine blood sugar levels, liver and kidney functions, Hepatitis B and Hepatitis C, HIV, blood count, etc.

If any volunteer shows past infection or any other infection or unsatisfactory blood parameters, then they are not involved in the trial. “The panel of tests is done on Day 1 and then repeated periodically, say on Day 15, Day 28, etc, to check the changes that may develop as an after-effect of vaccine administration. The candidates are tracked not just till the trial period, but for a few months after the trial gets over,” said Dr Dang.

Those who are not eligible include people with acute illnesses with or without fever at the time of experimental vaccine administration, history of laboratory-confirmed Covid-19, history of severe allergic reactions after previous vaccinations or hypersensitivity to any component of study vaccines, any confirmed or suspected condition with impaired/altered function of immune system, and pregnant women.