The administration of a booster third dose of mRNA vaccine (Pfizer / BioNTech or Moderna) to humans previously infected with the coronavirus will slightly increase their protection against the Omicron variantin relation to the two doses, according to two new scientific studies, one American and one Canadian.
The researchers, led by Dr. Margaret Lind of Yale University, did the pre-publication on medRxiv, according to Reuters. studied data on nearly 130,000 peopleof which 10,676 had been infected with the coronavirus (the vast majority from Omicron, while a smaller percentage from previous variants).
Two doses of the mRNA vaccine were found to improve the protection against Omicron in those previously infected with the coronavirus, but a third booster dose did not appear to provide a significant extra benefit.
A separate Canadian study, also pre-published in medRxiv, found that after the two doses, the supplements provided a marginal benefit over Omicron to people who had previously had a coronavirus (another variant) and thus acquired a natural immunity to some extent.
Without vaccination, a previous non-Omicron infection appeared to reduce the risk of Omicron re-infection by 44% (from 66% after 3-5 months to 35% after 9-11 months and less than 30% after one year). The more severe the previous infection, the greater the reduction in the subsequent risk of re-infection (from 8% for the asymptomatic to 68% for those who needed treatment).
The efficacy of the Omicron mRNA vaccine was significantly greater if one also had a previous Covid-19 infection. But beyond the two doses, it seemed that the third dose only marginally increased protection.
The message from the two studies, according to Lind, is “first, that people should get two doses of mRNA vaccine whether or not they have had a previous Covid-19 infection, and secondly, those who have not had a previous infection should get a booster dose and, thirdly, that people with a history of previous infections could take an adjunct dose, especially if they belong to a high-risk group for life-threatening complications, but keep in mind that the adjunct dose may not additional protection against infection, in relation to the two doses “.
Links for scientific pre-publications: (www.medrxiv.org/content/10.1101/2022.04.19.22274056v3 and www.medrxiv.org/content/10.1101/2022.04.29.22274455v1)
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