What ? Coronavirus News Live: Delhi records 1,534 new Covid-19 cases, 3 deaths; 2,054 fresh cases & two deaths in Mumbai

There is a renewed discussion on COVID-19 breakthrough infections (people who are fully vaccinated, yet testing SARS CoV2-positive). This is understandable, as with a fresh spike in COVID-19 cases in Indian states, a majority of patients are those who have received the mandatory two shots. Is this a reason for worry? The short answer is no. Let’s start with a few key points. First, with COVID-19, neither a past infection nor full vaccination prevents a subsequent infection. There are two different terms used to describe the situation. A second infection in a person with confirmed past infection is termed “reinfection.”  However, an infection in an individual, who has been vaccinated, is termed  “breakthrough” infection. It has got this interesting name as it arguably is a “breakthrough” for pathogens which could jump the immunity barrier. Second, is it possible to stop any future infection? The answer is only in a scenario of “sterilizing immunity.” This is a kind of immunity, which, once developed, is ready to clean up the pathogen once it comes in contact with the immune host. However, developing that kind of immunity is dependent upon multiple factors: host immune system, time since last exposure and/or vaccination, route of infection, pathogen’s incubation period and amount of viral exposure, among many others. There is no sterilizing immunity in true sense. Some diseases, such as smallpox (which was eradicated in 1980) and measles, come close to developing such immunity. However, even in those diseases, some re-infections have been reported. Third, natural infections, and as a rule for most pathogens, are more likely to provide stronger and long-lasting immunity than vaccines. We know one infection, with measles, provides nearly life-long immunity and protection. However, if a measles, vaccine shot is administered, the protective effectiveness is around 85 per cent. That’s why a second dose of measles vaccines is recommended, which brings effectiveness to around 95 to 98 per cent, still short of 100 per cent protection. Fourth, the level of immunity is also influenced by the route of infection. SARS CoV2 is mainly a mucosal infection, and immunity and protection against this type of infection is always weak and lower. Respiratory viruses, which infect through mucous membranes of the nose and throat such as SARS-COv2 and have a high propensity for mutation, are unlikely to provide sterilizing immunity. Fifth and most important, the use of the term “breakthrough infection” is misleading and not fully appropriate. It is now widely known that most SARS CoV2 vaccines, including those being used in India, have no evidence in reducing transmission. There is a consensus that vaccines prevent moderate to severe disease and hospitalization. Till now, only mRNA-based vaccines (Moderna and Pfizer-BioNTech) are known to have some temporary protection from infection and transmission as well. And even that protection from infection and reducing transmission declines rapidly after three months.  The role of non-mRNA COVID-19 vaccines in preventive transmission is unproven and unknown.  Therefore, terming SARS CoV2 infection in a fully-vaccinated person as “breakthrough infection” is akin to testing a very well-performing student of class V  for the syllabus of class VIII (in which he or she fails to perform well) and then arguing that she/he is not a good student. Clearly, it is a wrong measurement tool. We should not use the word “breakthrough infection” in the context of COVID-19 vaccines, at least for the two predominant COVID-19 vaccines being used in India.