CMAAO Coronavirus Facts and Myth Buster: Vaccine short-term safety

With input from Dr Monica Vasudev

1322:  What is known about the vaccines’ short-term safety?

NEJM Excerpts:

  1. Rare events will be reported, which will escalate the attention and worry that will be disproportionate to the actual risk. It will be important to put these rare events into perspective, highlighting the fact that these risks are considerably lower than the risk of getting sick with COVID-19.
  2. Both the mRNA vaccines are classified as reactogenic. This means that there will be some side effects in most people who will be vaccinated, which represents the quick immune response generated by these vaccines. These vaccines should be put in the same side-effect category as the recombinant shingles vaccine (Shingrix).
  3. The most common side effect is pain at the injection site, particularly in the first 24 hours following administration. About 1% of individuals in the trials reported the pain to be severe. Other relatively common side effects include fatigue and headache. High fevers are less commonly seen. These side effects often resolve within a few days and respond to acetaminophen or a nonsteroidal anti-inflammatory drug, like ibuprofen. Side effects appear to be more common in the younger recipients compared to the older subjects, and the second shot tends to induce more side effects vs. the first one.
  4. Bell’s palsy was more often reported among vaccine recipients compared to controls. However, the number of cases was not large enough to suggest that this was beyond the number that is naturally seen in populations of this size by chance.
  5. No cases of Guillain–Barré syndrome or transverse myelitis were observed.
  6. Hypersensitivity was noted equally in the placebo and vaccine groups in both the trials. However, following the distribution of the vaccines in the United Kingdom and the United States, there were reports of severe allergic reactions (anaphylaxis) soon after the first dose.
  7. The major suspect behind these reactions appears to be polyethylene glycol. This compound is present in both the vaccines. Owing to these rare events, administration of the vaccines is followed by a period of 15 minutes of observation. The duration is 30 minutes for those who have a history of severe allergic reactions of any kind.
  8. These allergic reactions are uncommon, and it is estimated that anaphylaxis will occur at about 1 in 100,000 doses.
  9. This rate is higher than what is seen with other vaccines, but considerably lower than the rate reported with penicillin (1 in 5000).
  10. As the vaccine is injected, the mRNA is taken up by the macrophages near the injection site. The spike protein appears on the surface of the macrophages, and incites an immune response that provides protection against natural infection with SARS-CoV-2.
  11. Enzymes subsequently degrade and dispose of the mRNA. There is no live virus, and no genetic material enters the nucleus of the cells.
  12. It is indeed brilliant how the insight put mRNA inside a lipid coating to prevent it from degradation.


Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA

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