Now and then we produce a TWiV that is focused on explaining basic aspects of virology. We call this series ‘Virology 101’. All the posts in this series are listed on this page with links back to the original post. If you start from the top, soon you will have a good basic understanding of virology. Repeated listening often fosters better comprehension.

For those who prefer reading, there is Virology 101 and Influenza 101 at virology blog.

If you have any questions, send them to

TWiV 39: Virus structure

TWiV 43: Virus classification

TWiV 46: Virus entry into cells

TWiV 49: Viral genomes

TWiV 60: Making viral RNA

TWiV 66: Reverse transcription

TWiV 96: Making viral DNA

TWiV 106: Making viral DNA II

TWiV 162: Transcription


TWiV 238: Lost in translation

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38 comments on “Virology 101

  1. jeromedumortier Feb 13, 2010


    I just discover your website with great Podcast about my field: virology. Because I am back in France and are still looking for a new position in virology and immunology, I appreciate your report on news in virology. I worked at OHSU in Portland OR on Human CMV as Postdoc and learn so much about host and virus interaction.
    My suggestion would be to cut your Podcast in 40 minutes but edit it each week instead each 2 weeks.
    Soon I will work at university I will suggest TWiV to my French coworker and students.
    Thank you very much
    Dr. Jerome Dumortier, in Rouen France.

  2. ericmakesthree Feb 24, 2010

    If this podcast had been around when I was at school I would have become a virologist – what a fascinating intriguing science

  3. dr.foster May 17, 2010

    Great stuff _ I was tuned into this podcast by a colleague and it is really the best science podcast I've found to date. Even though I've done work with viruses all my (admittedly short) career, listening to this just shows me how much more I still have to learn!

  4. the link to twiv 96 actually points to 97

  5. SaL Aboushoushah Apr 11, 2012

    the app in itunes is not free it is 4.99

    • loglet Sep 30, 2013

      Well it’s certainly free now in UK. the one I use is Podcasts.

  6. Peter Balfe May 8, 2012

    Why not run a TWIV on eIF4G and eIF2-alpha? there’s a heap of fun to be had there and valuable concepts to be learnt

  7. Thank you Dr Racaniello I have used your class lectures (with Dr Silverstein) to prep for USMLE
    Be blessed man!

  8. Dave_priyank89 Aug 3, 2012

    great knowledge

  9. Carlos Acosta009 Dec 4, 2012

    I wish I could take your class professor Racaniello

  10. I wonder if Dr. Racaniello offers online courses?

  11. P Yk Chong Jan 23, 2013

    Great website with useful resources than what I have in my university. Looking forward to meet Dr. Racaniello in the future. =) I love virology.

  12. Rob Loch Raineach Aug 26, 2013

    Coursera brought me over. Virology 101 is perfect. Great Pod cast. I am hooked.

  13. Makia Aqeel Sep 20, 2015

    I wish I could be your Mphil or phD student anyhow..

  14. Rowa Assayaghi Jun 17, 2016

    Hello prof
    why there is no HCV vaccine?

  15. Abhinav Purohit May 31, 2019

    I just wanted some suggestions on which books to read as a fresher to virology.
    So any suggestions are welcome.

  16. Cbanka Mar 10, 2020

    Great information about covid 19, thanks for all of you time sharing you wealth of knowledge with us!!!

  17. Susan Mar 14, 2020

    Where did this Corona 19 virus come from

  18. Greetings TWIVers,

    This John Ioannidis blog post so far makes the most compelling case for not over-reacting to covid19 (link below). His basic thesis is that the 3.4 % WHO fatality rate is meaningless because it is based on very poor data.

    This line really stuck with me: “some so-called mild or common-cold-type coronaviruses that have been known for decades can have case fatality rates as high as 8% when they infect elderly people in nursing homes. In fact, such “mild” coronaviruses infect tens of millions of people every year, and account for 3% to 11% of those hospitalized in the U.S. with lower respiratory infections each winter.

    This makes me wonder how many viruses went through the human population in recent decades without even being noticed. Could we have gone through several covid19-like events without anyone noticing? Or are there people on the look out for novel viruses which makes this scenario impossible? I guess what I am asking is the following: could there be other explanations that have more to do with hysteria and hospital systems being overwhelmed to explain what happened in Wuhan, Iran, and Italy?

    Warmest wishes from a crisp & sunny 7 C Berlin, Germany


  19. Margaret Waltz Mar 19, 2020

    Dr. Racaniello,

    I really love the show, thank you so much from an immunologist turned stay at home Mom turned Office Manager with not enough science in her life!

    I have two comments about the current SARS2 outbreak to share.
    1. “Case number” as a way of understanding what’s going on seems barely meaningful given how differently everyone is testing. Maybe we would be better off using “deaths” since that is not subjective, and relate that to exposed population (isn’t everyone exposed a case given zero immunity?).

    2. Coronavirus is like a tiny burr with the spikes… no wonder it grabs on so well! We could call it Burrvirus.

    Thanks again, my heart skips a beat when I get a new TWIV in my podcast feed.


  20. I can’t find a way to ‘subscribe’ to your podcasts. I’ve just discovered you and really appreciate what you have done AND what you are doing in this COVID-19 era. I want to keep connected to your work.
    Thanks so much.
    Mardi Crane-Godreau, PhD
    Geisel School of Medicine at Dartmouth
    & Bodymind Science, LLC

    • Charmaine Apr 22, 2020

      If you have iTunes you go here

      and on the left side, under the TWIV icon press subscribe, and depending on your settings it will download all, or most recent.

      Or on the website on the home page, you can either play each episode or you could choose the email option in blue underneath the player. I can’t insert a screen shot. You should see most recent on top of page from here

      If you had an older podcast app like Miro, you could subscribe with the RSS option

  21. R Niner Apr 3, 2020

    I used to take hydroxychloroquine. It is not a nice compound. It takes a month to build into your system when used for arthritis. There should be lots of people that can be surveyed to see if it stops Covid. Why hasn’t this been done? Every rheumatologist has patients

  22. Gail D Arnold, PhD Apr 18, 2020

    How does “GOF (gain-of-function) differ from mutation
    Or ‘genetic engineering’
    GOF is controversial/ethical
    Issue. Comment??thanks

  23. Julia Maresca Apr 22, 2020

    What guidance would you recommend for a patient who had covid-19 but is not exhibiting symptoms anymore.
    3 days after symptoms are gone and no fever for three days
    or 7 days
    or 14 days.
    Question: how long is COVID contagious?

  24. Rosa Romigosa Jun 18, 2020

    I began to hear your Podcast to improve my knowledge about The SARS-CoV-2 Pandemic, thank you for all the information, DR Rosa Romigosa.

  25. Victoria A Casetta Jun 24, 2020

    I am getting ready to fly back to the United States from southern China and I am curious about the lag time of the covid 19 virus. For example if I become infected how long will it take for me to be able to infect someone else? Thank you for your time and consideration.

  26. Dora Calott Wang Jul 11, 2020

    Can SARS-CoV2 and a common coronavirus infect the same host cell? If so, could a common coronavirus be similar enough to SARS-CoV2, that it could interfere with replication of SARS-CoV2? Common coronaviruses are endemic, and so if it is possible for simultaneous infection to occur, it is probably happening. Could it account for children not getting sick from Covid (because they are also getting infected from a common coronavirus)?

  27. I’m a lay person, and many of the things discussed are over my head, many things are, but somehow, TWIV, is one of my favorite podcasts.

    I know why. You have intelligent people who care who are witty and interesting to listen to. The team also strikes a balance of professionalism and empathy.
    I’m always happy whenever a new episode gets dropped into device. Keep up the great work. You guys provide a great calming effect in this time of crisis.


  28. Hello Vincent, TWiV et. al.
    I have been using your video “Threading the NEIDL” for teaching biosafety levels to my undergraduate class (as it is the only BSL-4 lab tour I know of).

    Now that we are going hybrid online, I need to have an ADA compliant close-captioned version of everything including your excellent BSL-4 lab video of the NEIDL for teaching undergraduate students.

    I am still planning to teach the microbiology lab live this fall with the experiments but I still need all materials ADA compliant.

    My IT department says I should request this TWiV episode as a close captioned .mp4 file from you (if you have it). Alternatively, we can take the native .mp4 file and CC to an ADA standard ourselves. A download link would be preferred since our email system might not handle this file. We are using the program Canvas as our online teaching platform (if that helps).

    Maybe you already posted the ADA CC version somewhere and I am not aware.
    Thank you and best wishes,
    James Harber

    Referencing this episode:

  29. Hey guys
    i got time to listen to your 2 podcasts and i tend to follow what measures virology plays especially when it comes to pandemic prevention.
    I will continue listening to the remaining ones.Thank you.

  30. Gordon Kelly Dec 14, 2020

    Suggest: 101 test!?

    Also: Maybe a 201 series, to include ie germinal center episodes rhapsody in b and/or pandemicky.
    Or, could be included in a bridge series to get up to speed for the immune podcasts.

  31. Eric Finzi Jan 20, 2021

    Dear All,

    Thank you for your contribution to informing everyone about virology in general and Covid-19 in particular. I would like to send you a paper of ours,
    “Zinc treatment of outpatient COVID-19: A retrospective review of 28 consecutive patients”
    that is in press at the J Med Virology. It will also be presented shortly at the upcoming Cold Spring Harbor Covid-19 conference.

    Feel free to discuss the results herein.


    Eric Finzi, MD,PhD

    George Washington School of Medicine

    Previous research has shown that zinc can interfere with proteolytic processing of polyproteins in RNA viruses1, and the RNA polymerase of SARS-CoV-12. Coronaviruses frequently cause the common cold. A recent meta-analysis of 7 randomized controlled trials (RCT’s) showed that zinc lozenges shortened the mean duration of the common cold by 33% (95% CI, 21-45%)3. Hospitalized COVID-19 patients taking supplemental zinc in addition to standard therapy were reported to have lower death rates4, and patients with lower zinc levels on admission had higher mortality5. We recently reported that 4 outpatient COVID-19 patients taking high dose oral zinc appear to recover shortly after initiation of zinc6.
    We retrospectively reviewed consecutive cases of laboratory confirmed COVID-19 (26 cases), or CDC case definition (2 cases), who were started on zinc gluconate/citrate lozenges (23 mg of elemental zinc, 21 patients) or zinc acetate lozenges (15 mg of elemental zinc, 7 patients), at a total dosage of 2 to 2.5 mg/kg/day. Patients were instructed to place one lozenge on their tongue q2-4 hours while awake, for a minimum of 10 days. Depending on weight, patients took between 6 and 12 lozenges daily. Written or verbal consent was obtained prior to treatment. The median number of days between symptom onset and initiation of zinc was 4 days, ranging from 1 to 21 days after onset of symptoms. The mean age was 40: 17 female, 11 male, 3 Hispanic, 3 Asian, 1 African-American and 21 Caucasian. Patients were contacted daily for symptom evaluation, and for side effects.
    Ten symptoms were scored according to a COVID-19 symptom checklist , categorized on a 3 point scale: 0-no symptoms,1-mild, 2-moderate, 3- severe. Fever and shortness of breath were further defined as follows: Fever 0 - 98.6, 1-  98.6-100.0, 2- 100.0 – 102.0, 3-  102.0. Shortness of breath (SOB) 1= moderate intensity exercise, 2= with walking on flat surface, 3= with any movement or at rest.
    Cough, nausea/vomiting, diarrhea, sore throat, headache, muscle/body aches, fatigue and loss of smell/taste were also assessed.

    All 28 patients were improved after 7 days of zinc. Symptomatic improvement began a mean of 1.6 days after zinc treatment. Patients 40 or older took an average of 2.1 days to improve vs 1.4 days for those under 40 ( p40 aged patients, vs 10 days vs 5 days), and type of zinc salt (zinc gluconate/acetate vs sulfate).

    The mechanisms by which zinc may help COVID-19 patients are unknown, but include direct inhibition of viral replication, improvement of mucociliar clearance of SARS-Cov-2, reduction of secondary bacterial infection, improvement of lung and kidney tissue healing after ischemia, modulation of T and B lymphocytes, and restoration of interferon-alpha production8,9. Zinc supplementation reduces the incidence of pneumonia10, and improves outcomes in diarrhea11. In addition, mild zinc deficiency is often present in those groups at highest risk from COVID-19; namely, the elderly, diabetic, obese, and hypertensive8.

    In mild cases of COVID-19 about 80 % of patients begin improving after day 10; 20% worsen the second week. Zinc treated patients began improvement after 1.6 days on average. Patients older than 40 began recovery slightly later than under 40; however, the clinical outcome at 7 days was the same, and this is not the typical COVID-19 course.
    A recent report12 by the CDC showed that among symptomatic adult COVID-19 outpatients, 35% were still symptomatic 2-3 weeks after testing positive. For those with SOB, one-third experienced these symptoms weeks later. By contrast, all 9 of our patients who were SOB began improving after 2 days, and none were SOB after 7 days. Except for fatigue, all 28 patients were symptom free after 3 weeks.
    This study has limitations intrinsic to any retrospective review: absence of blinding and a control group. However, given the low toxicity and cost of oral zinc, it would seem prudent to begin testing of zinc in a controlled trial.

    Conflict of interest: Eric Finzi and Allan Harrington have no conflicts of interest to report.


    1)Lanke K1, Krenn BM, Melchers WJ, Seipelt J, van Kuppeveld FJ.
    PDTC inhibits picornavirus polyprotein processing and RNA replication by transporting zinc ions into cells. J Gen Virol. 2007 Apr;88(Pt 4):1206-17.

    2)te Velthuis AJW, van den Worm SHE, Sims AC, Baric RS, Snijder EJ, van Hemert MJ. Zn(2+) inhibits coronavirus and arterivirus RNA polymerase activity in vitro and zinc ionophores block the replication of these viruses in cell culture. PLOS Pathog. 2010; 6:e1001176.

    3)Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open. 2017 May 2;8(5):2054270417694291. doi: 10.1177/2054270417694291.

    4)Carlucci P, Tania T, Petrilli et al. Hydroxychloroquine and azithromycin plus zinc vs hydroxychloroquine and azithromycin alone: outcomes in hospitalized COVID-19 patients Medrxiv doi:

    5) Jothimani D, Kailasam E, Danielraj S, Nallathambi B, Ramachandran H, Sekar P, Manoharan S, Ramani V, Narasimhan G, Kaliamoorthy I, Rela M. COVID-19: Poor outcomes in patients with zinc deficiency. Int J Infect Dis. 2020 Sep 10;100:343-349. doi: 10.1016/j.ijid.2020.09.014. Epub ahead of print. PMID: 32920234; PMCID: PMC7482607.

    6) Finzi E. Treatment of SARS-CoV-2 with high dose oral zinc salts: A report on four patients. Int J Infect Dis. 2020 Oct;99:307-309. doi: 10.1016/j.ijid.2020.06.006. Epub 2020 Jun 6. PMID: 32522597.

    7) Eby GA 3rd. Zinc lozenges as cure for the common cold–a review and hypothesis. Med Hypotheses. 2010 Mar;74(3):482-92. doi: 10.1016/j.mehy.2009.10.017. Epub 2009 Nov 10. PMID: 19906491; PMCID: PMC7173295.

    8)Wessels I, Rolles B, Rink, L. The potential impact of zinc supplementation on Covid-19 pathogenesis. Front Immunol 2020:11:1712

    9) Prasad AS, Beck FW, Bao B, Fitzgerald JT, Snell DC, Steinberg JD, et al. . Zinc supplementation decreases incidence of infections in the elderly: effect of zinc on generation of cytokines and oxidative stress. Am J Clin Nutr. (2007) 85:837–44. 10.1093/ajcn/85.3.837

    10) Sazawal S, Black RE, Jalla S, Mazumdar S, Sinha A, Bhan MK. Zinc supplementation reduces the incidence of acute lower respiratory infections in infants and preschool children: a double-blind, controlled trial. Pediatrics. (1998) 102:1–5. 10.1542/peds.102.1.

    11) Dhingra U, Kisenge R, Sudfeld CR, Dhingra P, Somji S, Dutta A, Bakari M, Deb S, Devi P, Liu E, Chauhan A, Kumar J, Semwal OP, Aboud S, Bahl R, Ashorn P, Simon J, Duggan CP, Sazawal S, Manji K. Lower-Dose Zinc for Childhood Diarrhea – A Randomized, Multicenter Trial. N Engl J Med. 2020 Sep 24;383(13):1231-1241. doi: 10.1056/NEJMoa1915905. PMID: 32966722; PMCID: PMC7466932.

    12) Tenforde MW, Kim SS, Lindsell CJ, et al. Symptom duration and risk factors for delayed return to usual health among outpatients with COVID-19 in a multistate health care systems network—United States, March-June 2020. MMWR Morb Mortal Wkly Rep. 2020;69:993-998.

  32. Hi, i am looking for a calculator to help guide a covid antigen testing program i am consulting on. I recall a calculator linked to your website that Daniel Griffin mentioned this summer on your show. But i can’t find it. I am trying to understand tradeoffs between different frequencies of testing asymptomatic workers using a test like BinaxNOW or Quidell. Thank you. Please email me at the email below or respond on website if possible.

  33. Coral Pollock Mar 27, 2022

    Thank you so much for this valuable resource. One great thing about the pandemic is my discovery of TWIV, and an unexpected thirst for learning virology basics! I thought this was only available at certain times of year. I am so excited your information is accessible any time.
    You are TRUE teachers, and deserving of much more funding and recognition.
    Thank you for keeping YouTube adfree so as not to interrupt the learning process. Again…TRUE educators, and wonderful folks.
    All the best!