by Amy B. Rosenfeld
I do not advocate testing for any person vaccinated against SARS-CoV-2 unless they display severe symptoms or live with those who for whom vaccines are not yet approved. I understand that testing and isolation are mechanisms to break virus transmission chains and were used at the beginning of the pandemic to control virus spread. To continue to follow this same philosophy today, more than 2 years later, suggests that little or no progress has been made to control or understand the virus and the pandemic. Furthermore, excessive testing inhibits our ability to make the proper ‘risk-benefit’ analysis necessary to generate programs that enable society to move forward with SARS-CoV-2.
My rationale for not testing vaccinated people is very simple and is based upon the precedents set for other pathogens for which vaccines exist. We do not test people for poliovirus, measles virus, influenza virus, or human papillomavirus after vaccination. If we tested the general public, vaccinated and unvaccinated, for rhinovirus or influenza virus infection/exposure, a significant amount of the population would be found positive. Following the CDC COVID-19 guidelines, those who test positive isolate for 5 days. Economies and society would grind to a screeching halt.
The measles, mumps, influenza and poliovirus vaccines were developed to prevent severe disease, not infection. These vaccines are some of our most successful biological products against infectious diseases. Many of these vaccines were developed when occurrence of severe disease caused by infection with these viruses was high or to mitigate the economic burden of the associated disease. Studies published investigating the mechanisms by which these vaccines protect us, demonstrated significant differences between the mechanisms of protection. For instance, administration of the oral poliovirus vaccine is via the natural route of infection, and confers immunity to the primary site of infection, the gut. It is gut immunity which is believed to protect the vaccinated from subsequent disease. Furthermore, when vaccination rates are high within a population, the community is protected, and virus transmission is interrupted. However, vaccinated people shed infectious neurovirulent poliovirus 30-90 days after vaccination into the environment, which can then infect those who are immunocompromised or unvaccinated and lead to the development of vaccine associated paralytic poliomyelitis. Approximately 1 in every 1.5 million vaccinees develop vaccine associated paralytic poliomyelitis.
The inactivated poliovirus vaccine functions differently. It is administered via the intramuscular route and prevents entry of the virus into the central nervous system and paralysis. When inactivated properly, no vaccinee will develop vaccine associated paralytic poliomyelitis. However, IPV does not elicit gut immunity; thereby, it does not prevent infection of the vaccinated or promote community protection. Those who are vaccinated will get infected and develop a low-grade fever but will not develop poliomyelitis. Consequently, infected vaccinees do not recognize they are infected.
To achieve global eradication of poliovirus, administration of both vaccines is required. And while the US and many other countries no longer administer the oral poliovirus vaccine to young children, if there is an outbreak of poliomyelitis, it is resolved first by administering OPV and then IPV. This policy is founded upon years of scientific studies to identify sites of virus infection and biology, to track transmission following vaccination and to understand how each vaccine works.
While the site of primary infection is mostly understood as the nasal and nasopharyngeal cavities, transmission of SARS-CoV-2 is not well understood. No published study has clearly demonstrated if people shed infectious virus following vaccination, if so for how long and if that is enough to transmit to others. Completion of such studies will take years. However, as a society, we do not want to wait for their completion. We are eager to resume activities that we did before the pandemic. Consequently, the question is what is required to resume these activities and what role does testing have in achieving this goal? Does the risk of resuming ‘daily life’ outweigh the costs of not doing so?
From the lessons of the poliovirus vaccine and others including measles, mumps and influenza a single vaccine will most likely be unable to both prevent infection and prevent transmission. The vaccine against human papillomavirus does prevent infection and transmission; however, this trait was a pleasant surprise. To fully understand how this vaccine is able to prevent infection and transmission much more research is required. However, during a pandemic there is no time for such lengthy studies.
Published work clearly shows that the COVID-19 vaccines protect against the development of severe disease and death. Testing does not change the case management of these individuals. If we want a vaccine that protects against infection, additional research and development is required.
This pandemic ends when more of us get vaccinated and when society accepts the fact that we will all get exposed or infected by SARS-CoV-2 at some point in time. Prudent use of these tools we have can prevent the development of severe disease, not burden our healthcare system. Working all together will prevent our economy from grinding to halt and enable us to resume the activities we participated in prior to the pandemic. A better use of our energy is finding ways to encourage vaccination of the vaccination-hesitant, and facilitate acceptance of the fact that unlike smallpox and poliovirus, eradication of SARS-CoV-2 is impossible. As populations become more and more immune to disease, the way our tools are used change. How testing vaccinated individuals promotes these changes is unclear.
Society accepts the risk of spreading rhinovirus, influenza virus and other respiratory pathogens to others including the unvaccinated and immunocompromised. The definition of a pandemic is not the number of the deaths, economic burden but the number of infections. Consequently, it is not correct to state that rhinoviruses are not etiologic agents of global pandemics. Rhinoviruses/enteroviruses are the most common human pathogens, and do cause pandemics, but we rarely die. Instead, they economically overwhelm society and we do not test for their presence.
Dr. Rosenfeld is a virologist at Columbia University.