#MSCOVID19: good news


Barts-MS rose-tinted-odometer: ★★★★★

The late late-breaking session at the MSVirtual2020 meeting, which covered COVID-19 has already received a lot of air-time on social media. The big-data alliance confirmed the Italian data, i.e. that people with MS (pwMS) on anti-CD20 are at higher risk of getting COVID-19 and severe COVID-19 (hospitalisation, intensive care admission and/or ventilation) compared to pwMS on dimethyl fumarate. Importantly there was no mortality signal, i.e. pwMS on anti-CD20 don’t appear to be at higher risk of dying from COVID-19 and its complications. This is very good news! 

However, the Big-Data alliance couldn’t confirm what the Italians have shown that treatment duration on an anti-CD20 is a risk factor. A clue to the latter is the observation that the COVID-19 risk was higher with rituximab compared to ocrelizumab in the Big-Data alliances graphs. As it is likely that rituximab-treated pwMS have been on treatment longer than ocrelizumab-treated patients would support this. Ocrelizumab has only recently been licensed and hence most people on ocrelizumab are likely to have been on it for a shorter period of time compared to rituximab-treated patients. 

Is all this good news? Yes, very good news. 

It clearly shows that people on anti-CD20 therapy have the ability to mount a robust immune response and recover from coronavirus infections, despite having a reduced B-cell and antibody response. This means that innate immunity and adaptive cellular immune responses are all that is required to recover from coronavirus and other viral infections. It will be important to study how robust the T-cell memory responses are post-COVID-19 in these patients as this will have implications for studying vaccine response when vaccines arise. What this means is that even if pwMS on an anti-CD20 don’t make an antibody response to a SARS-CoV-2 vaccine they may still have protective cellular immunity. This will also be good news. I sincerely hope Roche-Genentech and Novartis are planning to study vaccine responses in ocrelizumab- and ofatumumab-treated patients when the vaccines arrive. 

The observation that the longer you have been on an anti-CD20 the greater your chances of getting COVID-19 and severe COVID-19 implies the risk may be related to hypogammaglobulinaemia and blunting of past cross-reactive immunity from being exposed to other circulating community-acquired coronaviruses. I illustrate this in the following slide. In short pwMS on anti-CD20 therapy are shifted to the right and are less likely to have asymptomatic infections and more likely to have severe infections. 

This cross-reactive immunity to other coronaviruses may be the silver lining to the ominous grey clouds that have been hanging over us for months. It seems that between 40-60% of people in the general population have T-cell responses to SARS-CoV-2 without a history of having had COVID-19 and without an anti-SARS-CoV-2 antibody response. It now seems that these cellular memory responses protect these individuals from getting COVID-19. If this proves to be the case then herd immunity might be much higher than we realise and this could explain why the second surge in places like London and New York are much lower than other places that had smaller peaks during the initial wave of COVID0-19. 

If this background cross-reactive coronavirus immunity hypothesis, backed by the observations we see in pwMS on anti-CD20 therapy, turns out to be true we may have already reached herd immunity in London and are not far off it in other areas of the country. New models by Gomes and colleagues, at the University of Strathclyde, and Lourenco and colleagues, at the University of Oxford, suggest herd immunity may occur at levels of exposure of 20% or lower. If this is the case then we will see it first in London. So please watch the London COVID-19 numbers if they stay low this will be very good news. 

Gomes et al. Individual variation in susceptibility or exposure to SARS-CoV-2 lowers the herd immunity threshold. MedRxIV doi: https://doi.org/10.1101/2020.04.27.20081893

As severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spreads, the susceptible subpopulation is depleted causing the incidence of new cases to decline. Variation in individual susceptibility or exposure to infection exacerbates this effect. Individuals that are more susceptible or more exposed tend to be infected earlier, depleting the susceptible subpopulation of those who are at higher risk of infection. This selective depletion of susceptibles intensifies the deceleration in incidence. Eventually, susceptible numbers become low enough to prevent epidemic growth or, in other words, the herd immunity threshold (HIT) is reached. Although estimates vary, simple calculations suggest that herd immunity to SARS-CoV-2 requires 60-70% of the population to be immune. By fitting epidemiological models that allow for heterogeneity to SARS-CoV-2 outbreaks across the globe, we show that variation in susceptibility or exposure to infection reduces these estimates. Accurate measurements of heterogeneity are therefore of paramount importance in controlling the COVID-19 pandemic.

Lourenco et al. The impact of host resistance on cumulative mortality and the threshold of herd immunity for SARS-CoV-2. MedRxIV doi: https://doi.org/10.1101/2020.07.15.20154294

It is widely believed that the herd immunity threshold (HIT) required to prevent a resurgence of SARS-CoV-2 is in excess of 50% for any epidemiological setting. Here, we demonstrate that HIT may be greatly reduced if a fraction of the population is unable to transmit the virus due to innate resistance or cross-protection from exposure to seasonal coronaviruses. The drop in HIT is proportional to the fraction of the population resistant only when that fraction is effectively segregated from the general population; however, when mixing is random, the drop in HIT is more precipitous. Significant reductions in expected mortality can also be observed in settings where a fraction of the population is resistant to infection. These results help to explain the large degree of regional variation observed in seroprevalence and cumulative deaths and suggest that sufficient herd-immunity may already be in place to substantially mitigate a potential second wave.

CoI: multiple

Twitter: @gavinGiovannoni  Medium: @gavin_24211

About the author

Prof G

Professor of Neurology, Barts & The London. MS & Preventive Neurology thinker, blogger, runner, vegetable gardener, husband, father, cook and wine & food lover.


  • Then we can also say that anti CD20 therapies are not enough to stop EBV, since the aberrant response of the immune system will continue to occur.

  • Thank you for lifting the grey clouds you describe so well!

    What is the best way for the general public to keep track of the London numbers? Is there a specific place they are reported?

  • Can you comment on risk of irt, specifically Mavenclad and covid. Kind of makes sense that risk of severe disease not that high because depletion of T and B cells not complete and gradual. But numbers in studies above are small (n=10). Any personal experience in clinic?

    • The patients who have developed COVID-19 post-cladribine have done well; in fact very well. This is not surprising given the mode of action of the drug.

  • Re ‘….compared to pwMS on dimethyl fumarate.’
    🤔 should say other dmt?

    Re strong signal with rituximab
    🤔 is rituximab also positively associated with older age, progressive disease and being more disabled?

    • DMF being the most commonly prescribed of the mid-efficacy* DMTs is used the comparator. Interferon-beta, for example, reduces your risk of COVID-19 and severe COVID-19.

      * mid-efficacy is an average effect. I now realise that if you are responder to DMF you may be a super-responder and do as well as people on high and very high efficacy DMTs. I would estimate that 40-50% of pwMS do exceptionally well on DMF.

    • Re: “… rituximab also positively associated with older age, ..”

      This would have been controlled for in the analysis. I think it has to do with the duration of treatment. Neurologists have been using off-label rituximab for decades. In comparison, ocrelizumab is the newish kid on the block.

  • What is the best way for the general public to keep track of the London numbers? Is there a specific place they are reported?

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