Is my patient with Covid-19 immune to future infections due to the same virus?

Since Covid-19 is a new disease, it is unclear if our body’s immune response can protect us from future infections, and if so, for how long.

In a MedRxiv study involving 175 Covid-19 recovered patients (median age 50 y) with mild symptoms, the production of neutralizing antibodies (Nab) varied, with ~30% of patients considered to have “very low level” titers. So at least a subset of patients with mild symptoms may not produce adequate antibodies against Covid-19 despite seemingly uncomplicated recovery.  Whether these patients are at risk of re-infection with Covid-19 virus remains to be seen.1

In a study involving patients with Covid-19 (median age 62 y) of variable severity, the rate of seropositivity at 2-4 weeks was 88% or higher. However, despite development of antibodies against surface spike protein and internal nucleoproteins of SARS-CoV-2, the Covid-19 virus, viral RNA could be detected in the throat samples from a third of patients for 20 days or longer.2

In another study involving mild Covid-19 cases, despite seroconversion after 7 days in 50% of patients and after 14 days in 100% of patients, no rapid decline in pharyngeal viral load was noted. These findings raised doubts about the role of antibodies in clearing the virus.3

Somewhat more encouraging is the finding that experimentally infected monkeys rechallenged with Covid-19 virus after full recovery 28 days following initial infection seem to be protected against Covid-19.4 So there may be some protection for couple of weeks at least! 

Ultimately, whether immunity to Covid-19 will be like seasonal coronaviruses that cause common colds with unpredictable protection after 1 year, or more similar to that of SARS virus with persistence of antibodies for ~2-3 years, only time will tell. 4,5

Stay tuned!


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  1. Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications. MedRxiv preprint doi:
  2. To KKW, Tsang OWTY, Leung WS, et al. Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet 2020; March 23. (20)30196-1
  3. Wolfel R, Corman VM, Gugggemos W, et al. Virological assessment of hospitalized patients with COVID-2019. Nature (2020) .
  4. Bao L, Deng W, Gao H, et al. Reinfection could not occur in SARS-CoV-2 infected rhesus macaques. bioRxiv doi:
  5. Callow KA, Parry HF, Sergeant M. et al. The time course of the immune response to experimental coronavirus infection of man. Epidemiol Infect 1990;105:435-46.
  6. McKenna S. What immunity to COVID-19 really means? Scientific American, April 10, 2020.


Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Is my patient with Covid-19 immune to future infections due to the same virus?

My patient with diabetes mellitus is now admitted with pneumonia. Does diabetes increase the risk of pneumonia requiring hospitalization?

The weight of the evidence to date suggests that diabetes mellitus (DM) does increase the risk of pneumonia-related hospitalization.1-3

A large population-based study involving over 30,000 patients found an adjusted relative risk (RR) of hospitalization with pneumonia of 1.26 (95% C.I 1.2-1.3) among patients with DM compared to non-diabetics.  Of note, the risk of pneumonia-related hospitalization was significantly higher in type 1 as well as type 2 DM and among patients whose A1C level was ≥9.1  Another population-based study found a high prevalence of DM (25.6%) in patients hospitalized with CAP, more than double that in the population studied.2  A 2016 meta-analysis of observational studies also found increased incidence of respiratory tract infections among patients with diabetes (OR 1.35, 95% C.I. 1.3-1.4).

Not only does DM increase the risk of pneumonia-related hospitalization, but it also appears to adversely affect its outcome with increased in-hospital mortality.2 Among patients with type 2 DM,  excess mortality has also been reported at 30 days, 90 days and 1 year following hospitalization for pneumonia. 4,5 More specifically, compared to controls with CAP, 1 year mortality of patients with DM was 30% (vs 17%) in 1 study. 4

Potential reasons for the higher incidence of pneumonia among patients with DM include increased risk of aspiration (eg, in the setting of gastroparesis, decreased cough reflex), impaired immunity (eg, chemotaxis, intracellular killing), pulmonary microangiopathy and coexisting morbidity. 1,3,5,6

Bonus Pearl: Did you know that worldwide DM has reached epidemic levels, such that if DM were a nation, it would surpass the U.S. as the 3rd most populous country! 7

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  1. Kornum JB, Thomsen RW, RUS A, et al. Diabetes, glycemic control, and risk of hospitalization with pneumonia. A population-based case-control study. Diabetes Care 2008;31:1541-45.
  2. Martins M, Boavida JM, Raposo JF, et al. Diabetes hinders community-acquired pneumonia outcomes in hospitalized patients. BMJ Open Diabetes Research and Care 2016;4:e000181.doi:10.1136/bmjdrc-2015000181.
  3. Abu-Ahour W, Twells L, Valcour J, et al. The association between diabetes mellitus and incident infections: a systematic review and meta-analysis of observational studies. BMJ Open Diabetes Research and Care 2017;5:e000336. 
  4. Falcone M, Tiseo G, Russo A, et al. Hospitalization for pneumonia is associated with decreased 1-year survival in patients with type 2 diabetes. Results from a prospective cohort study. Medicine 2016;95:e2531.
  5. Kornum JB, Thomsen RW, Rus A, et al. Type 2 diabetes and pneumonia outcomes. A population-based cohort study. Diabetes Care 2007;30:2251-57.
  6. Koziel H, Koziel MJ. Pulmonary complications of diabetes mellitus. Pneumonia. Infect Dis Clin North Am 1995;9:65-96.
  7. Zimmet PZ. Diabetes and its drivers: the largest epidemic in human history? Clinical Diabetes and Endocrinology 2017;3:1  


My patient with diabetes mellitus is now admitted with pneumonia. Does diabetes increase the risk of pneumonia requiring hospitalization?