The criteria for defining the distribution of vaccines among different population groups should be based on existing scientific knowledge. In the case of people with previous SARS-CoV-2 and/or COVID-19 infection, information is still limited, as all Phase III clinical studies of approved vaccines have been conducted in an uninfected population.
Therefore, there is no solid scientific data to validate vaccination of the already infected population, and the logical conclusion is that it should not be recommended. The risk of this recommendation seems manageable given that we can consider that most people who have passed COVID-19 are protected against re-infection, at least for 6 months post-infection. A recent epidemiological study involving 12,364 healthcare workers with an average age of 38 years quantifies this protection at six months. The presence of antibodies is associated with 83% protection against active SARS-CoV-2 infection (PCR positivity during the study period), confirming the existence of protective immunity at levels comparable to those obtained by approved vaccines (Mahase, 2021).
Consistent with epidemiological data, different studies confirm the duration of neutralising antibody responses at least six months after infection. These antibodies show a rapid onset, a subsequent drop and stabilisation three months after infection, with half-lives of more than one year from this point, suggesting that immunity may be long-lasting. However, neutralising antibody titres are high in severely infected individuals, but a proportion of asymptomatic or mildly symptomatic individuals show low or undetectable levels after six months of infection (Pradenas et al. 2021).
Recommendation: although more evidence from different cohorts is desirable, these data support the repeated recommendation that persons with documented past COVID-19 infection should not be prioritised during vaccination campaigns (Sanjosé et al. 2020).
The lack of information on the duration of immunity produced by natural infection beyond six months post-infection and the comparative data with immunity achieved by vaccination, which is generally superior to that induced by natural infection, suggest that vaccination of infected persons would be desirable. But such vaccination would require only a single dose of vaccine (in vaccines where two doses are normally needed), which would be sufficient to ensure an optimal level of immunity.
Recommendation: a single dose of vaccine after six months of documented infection (once the immune response is stabilised) would therefore appear to be the optimal schedule for persons with documented SARS-CoV-2 and/or COVID-19 infection. Specific studies in this population are absolutely necessary to define the optimal schedule.
A direct consequence of these recommendations is the potential need for serological testing of the population prior to mass vaccination campaigns. Factors to be taken into account would be:
Recommendation: systematic screening would not be recommended at first.
You can see the references of the statement here.
This article was written by Julià Blanco, Silvia de Sanjosé, Josep M Miró, Quique Bassat, Magda Campins, Robert Guerri, Carles Brotons, Juana Díez, Mireia Sans, Olga Rubio, Adelaida Sarukhan, with the support of Antoni Plasència and Josep M Antó, from the Multidisciplinary Collaborative Group for the Scientific Monitoring of COVID-19.