Not long after scientists in South Africa discovered the Omicron variant of the coronavirus that causes Covid-19, a number of Western countries — including the United States — imposed travel bans on people traveling from southern African countries. The U.S. ban exempts American citizens and permanent residents.
Notably, Omicron has been identified in many other countries around the world, including the United States. Some data even suggests that it may have been circulating in Europe even before it was identified in southern Africa. Yet the bans remain.
President Biden acknowledged that the American travel ban was unlikely to stop the virus. But he justified it as a way of delaying the arrival of the new variant into the country. Others have justified the ban as a way to act “proactively” — as if there are no undesirable consequences of this policy.
Did the ban delay the arrival and spread of the new variant in the United States? How does it impact the efforts to control Covid-19 in the United States?
The science is nuanced. Even before the pandemic, scientists had studied the utility of travel bans after the emergence of a new respiratory virus. Most of the pre-Covid-19 pandemic research was conducted on potential influenza pandemics. Seasonal and pandemic influenza virus can be devastating, but it is less infectious than SARS-CoV-2, the virus that causes Covid-19.
To assess the infectiousness of a virus, epidemiologists use a unit of measure they call the basic reproduction number, or R0. It is derived from the average number of individuals a single infected person is statistically likely to infect in an otherwise uninfected and unimmunized population. The virus that caused the 1918 influenza pandemic had an R0 of 1.8, and the R0 for seasonal influenza ranges from 0.9 to 2.1, whereas the original strain of SARS-CoV-2 had an R0 of 2 to 3; the Delta variant has an estimated R0 of 6. While we don’t yet know the R0 for Omicron, it is likely to be substantially higher than influenza’s.
A 2014 review of scientific evidence conducted by a group of British researchers from Public Health England and the University of Nottingham concluded that travel bans can work but only for stalling the arrival of a pandemic influenza virus into a country. To effectively delay virus importation, a ban must shut down almost all travel into a country, the study found. But according to the researchers, even these drastic restrictions may have limited utility if the virus involved is moderately to highly infectious — which is the case with SARS-CoV-2 and its variants.
During the current pandemic, it is true that countries such as New Zealand and Australia have used travel bans to reduce importation of SARS-CoV-2. But their bans have been near-total, early, and paired with effective contact tracing and quarantine systems. Similarly, many small island nations such as the Polynesian country of Tuvalu — population approximately 12,000 — have kept the coronavirus out after severely restricting travel.
So, yes: Travel bans can work under limited conditions. But the Omicron-related southern Africa travel ban imposed by the United States is too selective, focuses on many countries where the variant hasn’t been documented and excludes many more where the variant has been detected.
If there were any doubts about the futility of this ban, reports of the Omicron cases outside southern Africa should put them to rest. In fact, there are substantially more countries with reported cases of Omicron outside southern Africa than in that region.
The travel ban is also not without cost. It could discourage countries from reporting new variants and emerging viruses.
Suppose you are a health minister somewhere in Africa and see some initial data indicating that a new variant is circulating in your country. Announcing the discovery would risk the imposition of capricious travel restrictions on your people. Do you tell the world?
The success of domestic efforts in the United States depends on what happens globally. A new variant or incomplete information about existing ones can undermine efforts to control the virus. It is in America’s interest that scientists, doctors and health officials everywhere do not feel conflicted in reporting relevant information rapidly and completely.
Rather than imposing arbitrary travel restrictions, countries can adopt less intrusive policies to slow the spread of the virus through international travel, including testing passengers before their departure or after arrival. Making proof of vaccination mandatory for international travel also helps limit importation of the virus.
The United States has, of course, already imposed new rules for all inbound travelers — citizens and permanent residents as well as foreign visitors — requiring a negative result of a test taken within a day of departure and proof of immunization. These rules further diminish the need for a blanket travel ban for a few countries.
The long-term solution, however, is to ensure that a high number of people around the world are vaccinated.
During the 2020 presidential campaign, Mr. Biden promised to have a science-based pandemic response. But his travel ban on southern African countries is not justifiable by science. Moreover, it makes Americans and others less safe by disincentivizing rapid reporting of new variants. It is time, then, for the United States to revoke the ban.
Saad B. Omer is the director of the Yale Institute for Global Health and a professor of internal medicine and epidemiology at the Yale School of Medicine and the Yale School of Public Health.