Differences Between Vaccine Induced Immunity and Infection Induced Immunity
What are the differences between vaccine induced immunity and infection induced immunity against COVID-19?
This is a big question that is best to break this down into smaller questions. I will also break up this topic into separate articles with part 2 next week.
Just what is meant by immunity?
The first thing to consider when talking about the differences between infection-induced and vaccine-induced immunity is to define just what is meant by immunity. Taber's Medical Dictionary defines immunity as “protection from diseases, especially from infectious diseases”. There are many different subtypes and degrees of immunity. For example the measles vaccine provides excellent protection against developing severe disease and the protection may last a lifetime. Reinfection after having had measles or “breakthrough infections” after vaccination are not common but do occur. People who do get infected after having received the 2 dose measles vaccine (MMR) tend to have very mild illness and are not as likely to pass on the virus to others. There were about 400-500 measles deaths reported annually in the US during the decade prior to vaccination. Outbreaks of measles have occurred in recent years in the United States but deaths from measles are extremely rare. However worldwide measles is still very deadly, for example there were about 207,000 deaths worldwide from measles in 2019. The measles vaccine is not perfect at preventing infection, but mass vaccinations have provided our country with almost complete protection against deaths from this extremely contagious virus.
If you have had COVID-19 can you get it again?
Reinfection after having COVID-19 appears to be uncommon within the first few months of having been sick. This seemed to be especially true prior to the rise of the more contagious variants. Early in the pandemic we did not see very many reinfections. There however is evidence now that reinfections are becoming more common. A study published in the MMWR on November 5, 2021, looked specifically at risk of hospitalization for those who had previous COVID-19 versus people who had been vaccinated. The researchers analyzed data from 201,269 hospitalizations for COVID-19 in that occurred from 1-2 -2021 through 9-2-2021 from a group of hospitals in 9 different states. The researchers did a number of statistical analysis two groups of patients; those who were unvaccinated but had a previous infection occurring 90–179 days earlier, and those how had 2 doses of an mRNA vaccine 90–179 days before hospitalization (and no record of previous positive SARS-CoV-2 test). Through a series of complex statistical analyses, the researchers came to the conclusion that vaccination provides better protection against hospitalization than a previous infection and this was most pronounced during the time period that the Delta variant was the predominant lineage.
The bottom line is that having COVID-19 once does not mean you will not end up in the hospital with COVID-19 if you get it again. If you have had COVID-19 getting vaccinated has been shown to decrease your risk of getting COVID-19 again.
How common is it to get COVID-19 after vaccination?
Infections are occurring in vaccinated people. There are more “breakthrough infections” since the Delta variant became the dominant viral lineage. There are a number of studies that have looked at the vaccine effectiveness against the Delta variant. What is being seen for numbers depends on the vaccine and population being studied but I think it is fair to say that with the mRNA vaccines the effectives is still about 70% - this is less than the 90%+ effectiveness rate against the original version of the virus - the vaccines are still very effective. Some early data suggest that those who have gotten a booster dose have very good protection against COVID-19 disease.
How likely is it to end up in the hospital with COVID-19 after vaccination?
While most breakthrough infections are mild, some vaccinated individuals are ending up in the hospital. However, most patients in hospitals because of COVID-19 have not been vaccinated. The vast majority of COVID-19 patients that need treatment in an intensive care unit are not vaccinated and almost all the people who are dependent on a ventilator have not been vaccinated. On December 16th several Nebraska infectious diseases specialists and officials from DHHS held a (Zoom) press conference updating the public on the current hospital crisis in the state of Nebraska. During that conference, Acting State Epidemiologist Dr. Matthew Donahue presented data on Nebraska COVID-19 hospitalizations. He stated that people who are not fully vaccinated are being hospitalized at rates 10 times higher than those who are fully vaccinated. Dr Donahue added that when they broke down the data based on age, they found that “unvaccinated 30 year old’s were filling hospitals at similar rates as fully vaccinated 80 year old’s”. Looking at those in Nebraska hospitals that were vaccinated they found that roughly half would have been eligible for a booster,
Next week I will continue discussion on the topic of gaining protection against COVID-19 through vaccination versus infection. If you have any specific questions, you would like answered please email them to newspaperquestions@gmail.com . Please keep in mind that information presented in these articles is intended to provide a medical perspective - the articles are not intended as a political statement for or against any public policy. Statements in these articles should be considered coming from myself, not from any organization I represent or my employer.
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