On March 24, in that date’s issue of Nature, it was first reported that there would be a temporary halt in the roll-out of the AstraZeneca vaccine for Covid-19. Unlike many of the vaccines, AstraZeneca is both inexpensive to produce (a few dollars per dose) and can be stored at temperatures much warmer than those used for the RNA vaccines, such as Pfizer-BioNTech vaccine.
Unlike the RNA vaccines, the AstraZeneca vaccine is made from a weakened version of a common cold virus from chimpanzees that is harmless to humans. That chimp virus has been further modified to carry a segment of genetic code from the Covid-19 virus. The chimp virus acts as a vector for the genetic sequence from Covid-19 and our cells then make proteins for both the viral vector from the chimp and from the pathogenic virus (in this case a protein from Covid 19). Our bodies then develop two specific immune responses to both. The chimp vector, also helps to boost the bodies immune response, leading to a more robust response. Neither the chimpanzee viral vector nor the protein from Covid-19 are sufficient to develop any adverse Covid-19 symptoms in humans, so the vaccine is safe, at least with respect to contracting Covid-19. The vaccine is administered in two doses about one month apart, and has proven to be roughly 80% effective against Covid-19 in a preliminary trial in which over 32,000 people were exposed to the virus after being vaccinated. For many countries, particularly those in the poorest countries in the world, this is the vaccine of choice, as it is relatively inexpensive and can survive transportation at relatively warm temperatures, in contrast to the RNA vaccines. It has been called a “win for the world”, but that is not where the story ends. From the date of the report in Nature, scarcely two weeks have gone by (until April 9, the airing of this blog) but things are changing rapidly. The use of the AstraZeneca vaccine has been halted in many countries due to a very rare side effect of the vaccine, that being the formation of blood clots. This has led to France suggesting that recipients of a first dose of AstraZeneca vaccine should follow up with a second dose of a different vaccine. Furthermore, the latest information regarding the Johnson and Johnson, single dose vaccine suggest a similar side effect, a very low rate of abnormal production of blood clots. Experts emphasize that the risk posed by the vaccine is tiny in comparison to the risks associated with Covid-19, however the risk is not zero. There is an unconventional piece of good news within this story. Not only did a relatively inexpensive virus, that can travel to tropical nations, get developed, but now problems associated with it are being thoroughly investigated before it is disseminated. This is not a one size fits all approach and public health officials are considering distribution with their eyes wide open. The AstraZeneca vaccine may not prove to be the panacea that developing countries were hoping for, but its scrutiny illustrates how careful the world is being with vaccination distribution, not just to the wealthy few, but to the world-wide population, regardless of income. And that, while a bit sobering, is good news in itself.