top of page
  • Raghav Sand

Covid-19 Vaccine Mix-and-Match: Yes, No, or Maybe!

Make no mistake, we are all part of one of the biggest science experiments the world has ever seen. One day, a vaccine variant is godsend, while the next day it is ‘put on hold until further notice’. One vaccine requires booster shots, but the other variant proclaims to be ‘one and done’. Medicine and biotechnology have made tremendous progress, but researchers can only tweak the final formula once they get the data about real-world vaccine efficacy. Something is better than nothing and in all the doom and gloom, this is a sliver of hope.

Many Paths, Same Destination

No two Covid-19 vaccines are the same; their development and formulation are as diverse as it can get. Though, vaccines like the ones from Pfizer and Moderna have one thing in common – both are mRNA vaccine. mRNA vaccines are a new type of vaccine to protect against infectious diseases. To trigger an immune response, many vaccines put a weakened or inactivated germ into our bodies; not mRNA vaccines. Instead, they teach our cells how to make a protein—or even just a piece of a protein—that triggers an immune response inside our bodies. That immune response, which produces antibodies, is what protects us from getting infected if the real virus enters our bodies. (For better understanding, a YouTube video link about mRNA vaccines is shared at the end of the article)

Getting the first dose of a two-dose vaccine is better than receiving nothing at all. Health officials have advised partly vaccinated individuals to not lower their guard in terms of following Covid-19-appropriate behaviour, and take the second dose with in the stipulated timeframe. There have been multiple revisions to the gap prescribed between the first and second dose of Covishield in India. ICMR has been frank to accept that the gap has been increased to administer as many first doses as possible in the shortest possible time. Ongoing studies about the efficacy of Covishield have also been kept in mind while increasing the gap to 12-16 weeks. Anxiety and nervousness about the availability of vaccine are being addressed by the union government on a daily basis.

For those who have taken the first dose of any Covid-19 vaccine, curiosity and concern have not completely settled down. Questions like ‘what if I don’t take the second dose with in the prescribed time’? or ‘Should I get another vaccine variant if the second dose of my first dose vaccine is in short supply?’ One of the more scientifically sound questions doing the rounds are: ‘will I have better antibodies if I mix-and-match my first and second dose?’ Questions like these are both legitimate and widespread.

Stick With Science

WHO’s Chief Scientist, Dr Soumya Swaminathan, in an interview to ‘Science in 5’ podcast tried to address common queries about the importance of schedule and mixing of doses of Covid-19 vaccine. On the subject of time between the two doses she said, “…in terms of missing the second dose or being delayed, it is important to get the second dose if the vaccine is a two-dose schedule. It doesn’t matter if it is early by a few days or late by a few days or even a couple of weeks. It’s important to go back and get that second dose because the first dose actually presents this new antigen to the immune system to prime it.

And the second dose is the one that really gives a boost to the immune system so that the antibody response, as well as T cell mediated response, they are very strong and they also develop a memory response, which then lasts for a long time, so that when the body sees this antigen again, this virus protein again, it knows that it needs to react quickly”.

Upon being asked about mixing the vaccine doses, Dr Swaminathan spoke on the basis of data available in February. “…immunologically, there are reasons why this would make sense. However, at the present time, there isn’t enough data for us to recommend this type of interchangeable two dose schedules. And so, for the time being, the policy advice that WHO has put out, which is the SAGE guidelines on how to use vaccines, we’ve done it for the Pfizer vaccine, the Moderna vaccine, the AstraZeneca vaccine, and currently SAGE is reviewing the data from the other vaccines that are in the pipeline. And so, we need to follow what’s in that policy advice and for the time being, it is recommended to have the second dose with the same vaccine as you had the first dose.”

The US Centers for Disease Control and Prevention (CDC) has warned against the mixing of vaccines, with the exception of those that are previously administered and are experiencing shortages. The side effects of vaccines have not been huge but they have been higher than expected. Vaccines often require more than one vaccination in the form of an initial prime, followed by a boost. This can be achieved by giving the same vaccine multiple times, known as ‘homologous boosting’, or by combining different vaccines targeting the same antigen, known as ‘heterologous boosting’.

Being able to combine different COVID-19 vaccines may be helpful to improved protection and/or to improve vaccine accessibility. This is why it is important to explore different vaccine combinations to help make immunisation programmes more flexible, by allowing physicians greater choice at the time of administering vaccines. It is also likely that combining vaccines may lead to improved immunity over a longer-period of time.

Evolving Situation

A lot will happen between now and by the time you are due to receive your second dose of the Covid-19 vaccine. Track and follow the up-to-date advice of health officials. As for those of you who are yet to receive the first dose, make sure you get the shot as and when available. For the select few who have received both the doses, you should pay attention to the announcement pertaining to any booster shots in the coming months, if any.

mRNA Vaccines, Explained

bottom of page