What we really know about waning COVID-19 immunity
Vaccines are still extremely effective at preventing severe disease. Waning antibody levels doesn’t always translate to lessening immunity.
- 1 October 2021
- 4 min read
- by Priya Joi
Many countries are charging ahead with the roll-out of COVID-19 vaccine boosters amid reports that vaccine-triggered antibodies tail off faster than we might have predicted, despite little evidence for the need for boosters in the general population.
Scientists are trying to calm fears over waning immunity, saying that the evidence for it has been overblown.
Vaccines are primarily designed to prevent severe disease and death rather than any infection at all – if an infection caused only mild disease it wouldn’t be worth the enormous cost of designing and rolling out a vaccine.
Antibodies aren’t the only marker of immunity
Reports of waning immunity, for which waning antibody levels are often used as a proxy, may seem to dull the sheen of COVID-19 vaccines, hailed as an incredible scientific achievement and our path out of the pandemic.
But it is entirely normal for antibody levels to drop off after our immune systems are first triggered into action – if they didn’t, we would harbour high levels of antibodies to almost every infection we’ve ever encountered, which would be biologically challenging.
Not only that, but conflating antibody levels with our level of immunity is flawed. While it’s true that, in general, antibody levels spike after infection or vaccination, people differ in their level of response, which is why taking an antibody test after vaccination can't prove anything. It also obscures the complexity of our immune reaction.
Neutralising antibodies are just one part of the package – our bodies also produce plasma cells and memory cells that remember a given pathogen and can be reactivated quickly to produce more antibodies if they encounter it again. There’s evidence to suggest that some of these plasma cells live in our bone marrow for months or years, and could produce antibodies for years to come.
Protecting against severe disease
Reports of breakthrough infections (i.e., infections in people who are already vaccinated) might seem alarming but they are expected.
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Vaccines are primarily designed to prevent severe disease and death, rather than to stave off any infection at all – if an infection caused only mild disease it wouldn’t be worth the enormous cost of designing and rolling out a vaccine. So, the goal is not to get to zero new infections, but to ensure that severe disease is stopped and that any infections that do happen are manageable.
Overwhelmingly, COVID-19 vaccines have shown that they are capable of doing that. A review in The Lancet of the evidence for booster shots showed that COVID-19 vaccines are highly effective at preventing severe disease, even in the face of new variants.
To boost or not to boost
Booster doses may be beneficial for people who are extremely vulnerable or immunocompromised. But using them in the general population would suggest that either existing vaccines are not effective against new variants of COVID-19 (when all the evidence is that they are effective, albeit with a small reduction in the effectiveness) or that immunity wanes so quickly that the already-vaccinated are at risk of serious cases of COVID-19.
Neither of these scenarios are true at the moment, though that has not stopped high-income countries rolling out booster programmes, even while only around 2% of people in low-income countries have received their first dose.
Researchers writing in the British Medical Journal point out that “the long term effect of boosters on reducing infection, transmission, and hospital admissions remains unknown”. They add that while boosters increase antibody levels, they have not been shown to augment the memory cell responses responsible for long term protection against severe disease.
Focusing on waning immunity therefore not only threatens vaccine confidence but also, say the researchers, “diverts attention and limited vaccine supplies away from the urgent need for primary vaccination of people with no immunity, particularly in low- and middle-income countries”.
