Bioethics Forum Essay
Nope. A Covid-19 Travel Pass isn’t Just like the Yellow Card.
Those who promote Covid-19 travel passes to facilitate safe international travel (such as the Green Pass in Israel or the Digital Green Certificate in the European Union) often cite the Yellow Fever International Certificate of Vaccination and Prophylaxis (sometimes called the Yellow Card) as precedent. In accordance with WHO International Health Regulations, it provides proof of vaccination against yellow fever and allows individuals to cross certain international borders. In fact, however, there is very little in common between Covid-19 travel passes and the Yellow Card; they differ in their public health goals, their scientific rationale, and the practicality of their implementation.
Citing the Yellow Card as precedent for Covid-19 travel passes that exempt those with proof of vaccination from testing and quarantine mandates when crossing certain borders is an erroneous policy assumption that could prolong the pandemic and imperil global health.
Public Health Inconsistencies
Yellow fever is a vector-borne disease that relies on infected Aedes and Haemagogus mosquitoes to transmit the virus between humans. Yellow fever vaccination protects both individuals and the communities those individuals are traveling to and from. Proof of yellow fever vaccination protects the health of people traveling to nations where yellow fever is endemic–parts of Africa, Southeast Asia, and Central and South America. The Yellow Card also prevents travelers who visit endemic areas from introducing yellow fever into other countries where the mosquito vector thrives.
In contrast, Covid-19 is a communicable disease directly passed from person to person. Anybody in the world can contract Covid-19, making it a global challenge, with hotspots changing as the various waves of infection move through different populations. Covid-19 travel passes are proposed for the singular purpose of protecting populations that have yet to reach community-level immunity (herd immunity) from foreign travelers who could be carrying the SARS-CoV2 virus and its emergent variants.
Proof of vaccination by foreign travelers can only protect communities of unvaccinated individuals (those who can’t access vaccines, those who can’t be vaccinated like young children, and those who choose not to be vaccinated) if the authorized vaccines prevent transmission. The WHO-approved yellow fever vaccine prevents the spread of the disease because it is 99% effective at providing immune protection and thus protection from vector-borne transmission. All of the Covid-19 vaccines currently in use are effective at protecting vaccinated individuals from severe Covid-19 and death, but their efficacy in preventing clinical Covid-19 ranges from just over 50% to 95%. This means that a vaccinated individual may still be able to contract Covid-19, shed the virus, and infect others–a risk that is likely to increase with the emergence of new variants. A recent study in the New England Journal of Medicine suggests that Pfizer-BioNTech vaccine efficacy in preventing Covid-19 infection in vaccinated individuals dropped from 89.5% to 75% when confronted with the B.1.351 variant.
The diversity of Covid-19 vaccines in use worldwide marks a stark departure from yellow fever vaccines. There is a single type of yellow fever vaccine worldwide – all such vaccines contain live attenuated virus. Four WHO pre-qualified manufacturing facilities fulfill global supply. In contrast, as of May 4, 2021, there are 19 Covid-19 vaccines at various levels of approval registered with the WHO. These include four different types of vaccines–whole virus, protein subunit, viral vector, and nucleic acid (RNA and DNA). These vaccines are being manufactured in dozens of facilities around the world. Covid-19 vaccine efficacy varies not only among the vaccines, but also among the manufacturing facilities. For example, when produced in the Sinovac’s facility in Brazil the Coronovac vaccine has an efficacy rate of 51% at preventing clinical Covid-19, as compared to an efficacy rate of 91% when produced in Turkey.
Under the WHO’s International Health Regulations, the yellow fever vaccination certificate is now valid for a traveler’s lifetime, whereas proposed dates for validity for Covid-19 vaccination certificates are educated guesses at this point, and likely a moving target across different vaccines.
Once vaccinated with a single dose of the yellow fever vaccine, an individual is forever protected from infection and from transmitting yellow fever. This is known because the yellow fever vaccine has been in use since the 1930’s, making lifelong clinical assessment possible. Covid-19 vaccines haven’t been in use long enough to know if immunity lasts much beyond eight months. Currently, every authorized Covid-19 vaccine is still under emergency use listing at the WHO (status under emergency use is another potential challenge to implementation, but one better left to our legal colleagues to unpack). These scientific uncertainties, along with inequitable global vaccine distribution and its attendant ethical risks, are why the WHO currently advises against the use of proof of Covid-19 vaccination for international travel.
Given these significant differences we believe it is imperative to set aside the oft-repeated suggestion that the Yellow Card is a useful precedent for the introduction of proof of Covid-19 vaccination for international travel. Following such precedent will endanger the global community and could prolong the pandemic.
Natalie Kofler is the founder of Editing Nature, leads curriculum development for the Scientific Citizenship Initiative at Harvard Medical School, and is a visiting fellow at the E.J. Safra Center for Ethics at Harvard University, Twitter: @NatalieKofler. Françoise Baylis is University Research Professor at Dalhousie University in Halifax, Canada, Twitter: @FrancoiseBaylis.