Mixed vaccine doses: safety, effectiveness, and flexibility

Ground Report | New Delhi: Mixed vaccine doses; Canadian Prime Minister Justin Trudeau, last Friday, took his second Covid-19 jab: a shot of the Moderna vaccine. Since his first jab in April was of the AstraZeneca vaccine, this shot marked him as one of the increasing numbers of people who have taken mixed vaccine doses. German Chancellor Angela Merkel also received the same combination, getting her second jab in June. But is it more effective, or even safe, to take a different vaccine for the second jab?

Mixed vaccine doses; Concerns

There are some very valid concerns regarding mixing and matching vaccine doses. Doctors and researchers alike point out that different vaccines are manufactured in different ways and each of them initiates a different response from the immune system. While some believe that based on the principles of how vaccines function, mixed doses should work, others are still skeptical.

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Moreover, an Oxford University-led study (Com-Cov), in May, found that mixing vaccines caused more severe side effects. Researchers attributed this to the shorter intervals between the vaccine doses. However, this is still the cause of skepticism among some medical practitioners and researchers.

Mixed vaccine doses are safe and effective

The Com-Cov study previously mentioned evaluated the efficacy of mixed doses of Pfizer and AstraZeneca vaccine in comparison with either two doses of Pfizer or of AstraZeneca. It concluded that all vaccinations worked well in building up immunity. Furthermore, it found that two Pfizer doses and mixed doses are both more effective than two AstraZeneca doses.

Preliminary, small-scale trials have proven that mixed vaccine doses are not only safe but also more effective than some standard doses. However, to generalise the results of this study on mixed doses to over 16 vaccines approved for use by various countries, more extensive trials, and long-term monitoring are required. These requirements have also become important in light of the concerns raised.

Vaccine rollout flexibility

The success of mixed vaccine doses opens up new possibilities, especially for countries that are struggling with providing citizens the same vaccine for the 2nd dose on time due to the unavailability of the same type of vaccine. This means that vaccination drives can be timely and reliable.

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Current use of mixed doses

Many people all over the globe have received mixed doses. After receiving reports of AstraZeneca-related rare blood clots, several countries banned the vaccine. This left the people who had taken AstraZeneca as their first dose with no other choice but to take a different vaccine for their second dose.

Countries such as Canada and Germany have also issued recommendations for people to get mixed vaccine doses. Trudeau and Merkel have demonstrated confidence in this recommendation by taking mixed doses themselves.

In India, towards May-end, 20 people in Uttar Pradesh were accidentally given a shot of Covaxin after having received Covishield as their first dose.

So far, receiving a mixed vaccine dose hasn't resulted in any serious health consequences. In fact, they have demonstrated benefits such as increased efficacy and the possibility of flexibility in vaccination rollouts. This mix and match policy has also received the green light from some countries. After an extensive study, this practice will probably come into effect in India as well.

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