Sunday, October 31, 2021

CDC Science Brief: SARS-CoV-2 Infection-induced and Vaccine-induced Immunity


Credit ACIP/CDC    
#16,286


Yesterday, in MMWR: Vaccine or Post-Infection Induced Immunity to COVID19 - Which is more protective?, we looked at Friday's MMWR release showing previously infected individuals were 5.5 times more likely to be reinfected with Delta than a vaccinated person was to having a breakthrough infection.

As you might imagine, there has been an immediate pushback on social media - primarily by those who view vaccines negatively - who maintain (and cite their own studies) that `natural immunity' is equal to, or superior to, what is provided by the vaccine.  

While post-infection acquired immunity is real (and widely acknowledged by the scientific community), you rarely hear proponents of this `all natural' process mention the  5+ million people who have died going this route. 

Admittedly, rare adverse events have been attributed to the vaccine - but with 3 billion people fully vaccinated around the globe - the number of deaths and serious injury pale in comparison to the carnage the virus has visited over the past 2 years. 

While Friday's MMWR release was the latest scientific paper on this subject, it is far from the only one. On Friday the CDC also released a lengthy Science Brief - with nearly 100 references cited - on the topic of acquired immunity (via infection or vaccination). 

There is undoubtedly a lot we still don't know about COVID immunity, and our current understanding may change over time. Or the virus could change tomorrow, rendering all of this moot. 

But right now, the preponderance of evidence strongly indicates that vaccination is the not only the safest, but the most effective way, to gain immunity to the virus.  Yes, it may require boosters.  But `natural' immunity wanes over time, too. 

I don't expect this Brief to change the mind of anyone who is staunchly in the anti-vaccine camp, but it may provide some reassurance to those who are subjected daily to misleading messaging on social media about the supposed dangers of the vaccine. 

I've only posted a few excerpts from a much longer science brief.  Follow the link to read it in its entirety. 

Science Brief: SARS-CoV-2 Infection-induced and Vaccine-induced Immunity

Updated Oct. 29, 2021 


This brief provides an overview of the current scientific evidence regarding infection-induced and vaccine-induced immunity, including both peer-reviewed and preprint publications, as well as unpublished CDC data. Although comprehensive, it is neither a formal systematic review nor meta-analysis. New data continue to emerge, and recommendations (the science brief, this webpage, etc.) will be updated periodically, as needed.

Recovery from many viral infectious diseases is followed by a period of infection-induced immunologic protection against reinfection. This phenomenon is widely observed with many respiratory viral infections, including both influenza and the endemic coronaviruses, for which acquired immunity also wanes over time making individuals susceptible to reinfection.

CDC continues to recommend COVID-19 vaccination for all eligible persons, including those who have been previously infected with SARS-CoV-2.


Executive Summary

Key findings and considerations for this brief are as follows:
  • Available evidence shows that fully vaccinated individuals and those previously infected with SARS-CoV-2 each have a low risk of subsequent infection for at least 6 months. Data are presently insufficient to determine an antibody titer threshold that indicates when an individual is protected from infection. At this time, there is no FDA-authorized or approved test that providers or the public can use to reliably determine whether a person is protected from infection.
    • The immunity provided by vaccine and prior infection are both high but not complete (i.e., not 100%).
    • Multiple studies have shown that antibody titers correlate with protection at a population level, but protective titers at the individual level remain unknown.
    • Whereas there is a wide range in antibody titers in response to infection with SARS-CoV-2, completion of a primary vaccine series, especially with mRNA vaccines, typically leads to a more consistent and higher-titer initial antibody response.
    • For certain populations, such as the elderly and immunocompromised, the levels of protection may be decreased following both vaccination and infection.
    • Current evidence indicates that the level of protection may not be the same for all viral variants.
    • The body of evidence for infection-induced immunity is more limited than that for vaccine-induced immunity in terms of the quality of evidence (e.g., probable bias towards symptomatic or medically-attended infections) and types of studies (e.g., mostly observational cohort studies, some retrospective immunity versus a mix of randomized controlled trials, case-control studies, and cohort studies for vaccine-induced immunity). There are insufficient data to extend the findings related to infection-induced immunity at this time to persons with very mild or asymptomatic infection or children.
  • Substantial immunologic evidence and a growing body of epidemiologic evidence indicate that vaccination after infection significantly enhances protection and further reduces risk of reinfection, which lays the foundation for CDC recommendations.
(SNIP)

Conclusions

Multiple studies in different settings have consistently shown that infection with SARS-CoV-2 and vaccination each result in a low risk of subsequent infection with antigenically similar variants for at least 6 months. Numerous immunologic studies and a growing number of epidemiologic studies have shown that vaccinating previously infected individuals significantly enhances their immune response and effectively reduces the risk of subsequent infection, including in the setting of increased circulation of more infectious variants.

Although the Delta variant and some other variants have shown increased resistance to neutralization by both post-infection and post-vaccination sera in laboratory studies, observed reduction in effectiveness has been modest, with continued strong protection against hospitalization, severe disease, and death.

Multiple studies have shown that antibody titers correlate with protection at a population level; however, data are presently insufficient to determine an antibody titer threshold that indicates if an individual is protected from infection. At this time, there is no FDA-authorized or approved test that providers or the public can use to reliably determine whether a person is protected from infection.

CDC will continue to follow and evaluate evolving scientific evidence in these areas and update recommendations accordingly.
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