Vaccines approved so far in the United States have been highly effective not just against preventing symptomatic infection but more importantly against severe Covid leading to hospitalization and death, and also – we are learning – against asymptomatic infection which means vaccination cuts down on spread of the disease. We just do not know how long this protection lasts because not enough time has passed yet to make this determination. And that’s a problem for policymakers as they consider whether to open up travel without testing or quarantine to those who have been vaccinated.
This is a problem with the idea of a vaccine passport, that we do not know how such a document should be valid for, since we do not know how long conferred protection lasts. Conventional wisdom is that we’ll need booster shots, and studies are progressing now to determine when, however it’s also likely that protection will last for some time albeit waning over time.
The CDC says, “We don’t know how long protection lasts for those who are vaccinated.”
We do know that natural immunity lasts quite some time for most people who have been infected, beyond when they show antibodies. While there’s concern about re-infection from the South African and Brazilian strains of the virus, and there’s some evidence for this, documented reinfections remain limited even as the virus has changed and there’s little indication (yet) that reinfections tend to be as or more serious compared to original infections. Approved vaccines against Covid-19 generate greater anitbody responses to the virus than are found in recovered patients.
Ultimately we don’t know how long protection against Covid-19 from vaccines will last, because there hasn’t been enough time that’s passed to tell us. It was just one year ago today that the first dose of the Moderna vaccine was given to a patient in a clinical trial, for instance.
In other words, we can’t really know how if protection lasts a year until a year has passed. We can’t know if protection lasts two years until two years have passed. What we can do is test immune response over time and if it declines we can project that out and make educated guesses.
The Points Guy answered the question about how long protection lasts but I don’t think the metric they offer is correct since it won’t merely be a function of antibody levels in those who have been vaccinated,
“We currently do not know, as we are living through the experiment,” said Dr. Jenny Yu, the senior manager of medical integrity at Healthline (which is owned by Red Ventures, as is The Points Guy). “As time passes with the first group of people having received the vaccines as part of the clinical trial, their antibody levels will inform us how long this immunity will last.”
In order to determine how long protection lasts, we’ll need:
- Tracking vaccinated individuals over a period of time to see when their immunity wanes. We’ll no longer have a placebo group to compare against but can make statistical comparisons against more recent vaccinations, against those who have chosen not to get vaccinated, and against earlier periods.
- Testing immune response in the blood of vaccinated individuals over time. Contra The Points Guy it’s not drawing blood and testing for antibodies that will tell us how long immune response lasts, but rather exposing drawn blood to SARS-CoV-2 and watching immune response – antibodies may wane without the virus present but looking only at antibodies misses the role of t-cells in response to virus exposure as well as memory B-cells.
- Larger data sets than those who participated in the first trial since different people have different immune reactions. The first Moderna trial gave different doses to 45 young, healthy adults. That doesn’t tell us how long protection lasts across a variety of age groups and physical conditions even now a year later.
There are now human challenge trials moving forward in the U.K. and that would be another way of testing continued efficacy – exposing vaccinated people to the virus after a period of time to see whether they continue to have an immune response. We’d likely need more fool-proof treatments before the medical establishment considered this ethical here for this purpose.
It’s the uncertainty that makes policymaking here difficult. While The Points Guy also noted that,
New York State announced earlier this week that it would ease entry and quarantine requirements for those who have been fully vaccinated against COVID-19. Now, domestic travelers no longer have to quarantine if they’ve been vaccinated within 90 days.
However this is no longer fully accurate. This change was made two weeks ago (March 3, not this week) and subsequently the state declared that domestic travelers will not have to quarantine at all starting April 1 whether vaccinated or not.
Nonetheless New York’s initial plan to require quarantine for arriving passengers who had been vaccinated after 90 days reflected the uncertainty surrounding duration of protection. We know that it lasts more than 3 months and are continuing to see data on just how much more.