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I am a senior, who will turn 73 in June. About a year ago I got the primary Moderna vaccination series. Last September, when the FDA and CDC were considering boosters, everyone seemed to agree that seniors needed them, but the government only authorized them for seniors who had gotten the Pfizer vaccine. I felt this was unconscionable and decided to take matters into my own hands. I went to a local pharmacy and got a third Moderna shot by telling them I had a compromised immune system. About a week ago I got a fourth Moderna shot by the same procedure. How much additional protection did I receive by getting the fourth (full strength) Moderna shot?
Currently, anyone age 50 years and older may get a second booster dose, which should be at least 4 months from their first booster dose. Also, for persons who received the Moderna vaccine as the initial 2-doses (primary series), these booster doses may consist of either mRNA vaccine (Pfizer or Moderna).
The protection afforded from the second booster dose is not as large, by sheer magnitude, as the primary series or the first booster dose. However, this is partially because these second booster doses are being deployed when viral transmission cases are approaching the lowest levels recorded (albeit with some local surges in some locales). There is some evidence that protection against infection (including mild infections which do not require hospitalization) may be of shorter duration (1-2 months), but this could be an effect of the Omicron subvariants which we know are much more transmissible. However, the protection against hospitalization and death appears to be longer-lasting.
The specific question you ask for “How much additional protection did I receive?” might be answered by data from Israel; the figure below is a summary slide from a recent CDC ACIP meeting (slide #32, )
In Israel, 4th doses (second booster doses) of Pfizer mRNA vaccine were administered beginning in January 2022 and the incidence of infections were followed. When comparing the effect on prevention of infection (including mild disease) and severe disease, there was a significant reduction in both infections and severe disease with the second booster compared to persons receiving only the first booster. This study did not compare the effect of the second booster against the unvaccinated or those only receiving the primary series, but you can imagine that those effects would be much larger.
Therefore, I want you to feel confident that you have improved your protection against Covid and have made the correct decision.
