Since the start of the COVID disease, the virus (SARS-CoV-2) has changed, creating new versions of itself (variants). Vaccines to prevent COVID were made using the structure of the first virus, not the new versions. Omicron was the most common variant when researchers from Israel looked at giving a fourth dose of the vaccine to people who were at a greater risk from the virus.

Using the Israeli Ministry of Health database, researchers studied data on 1,252,331 people who were 60 years old and above, and who were able to be picked for a fourth dose from January 10 through March 2, 2022. They compared the rate of COVID infection and severity starting eight days after a fourth dose in people who had received only three doses and also in people who had received a fourth dose less than a week earlier. They checked up with people for six weeks. Those who had COVID before that were not included

Benefits of a fourth dose

The researchers found a small benefit from the fourth dose. For instance, compared to getting only three doses at least four months earlier, the fourth dose lowers the risk of severe infection as well as the chances of getting infected. However, because researchers only monitored people for four to six weeks, it is not clear if the benefit from a fourth dose is lasting. It was clear that protection against severe disease lasted until the end of the study, but the reduced risk of getting infected did not last as long. A fourth dose did not raise the risk of getting COVID; therefore, repeated vaccination is safe.

Deciding whether or not to get a fourth dose of the vaccine is not simple. It is important to think about how strong your ability to fight disease is, how present the virus is in your community, and how long it has been since your previous vaccine dose. These new findings also make clear that the virus is constantly changing and that, based on how it changes, new vaccines will continue to be needed.


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