The Janssen vaccine (Johnson & Johnson) can be used to vaccinate the population in one or two doses, in combination with another vaccine for a second dose or in the case of two doses over a period of 2-6 months, depending on the epidemiological situation prevailing in each country.
The World Health Organization (WHO) Committee of Experts on Immunization concludes on this recommendation regarding the immunization of the populations of the states with this vaccine, giving governments the opportunity to develop the immunization policies they need.
According to the Agency, in some cases, the use of a single dose may have advantages, as many countries face severe limitations on the adequacy of vaccines, combined with an increasing number of cases that place a heavy burden on their health system. In these cases, a single dose of the vaccine is effective and allows rapid vaccination coverage, which in turn will reduce the burden on health systems preventing serious disease. A single dose may also be chosen to vaccinate populations living in inaccessible areas or in conditions of conflict or insecurity.
The use of a second dose may be appropriate as vaccine supplies or accessibility increase. Countries should consider offering a second tranche, starting with higher priority populations (eg health workers, the elderly, people with comorbidities) as defined in the WHO Priority Charter. In this case, giving the second dose will result in increased protection against the symptomatic infection and against the serious disease.
A heterologous vaccine (e.g., a COVID-19 vaccine from another approved vaccine platform) may also be considered for the second dose.
In 2 or 6 months
Regarding the timing of the second installment, countries can also take advantage of the possibility of dosing between 2 and 6 months.
A second dose 2 months after the initial dose significantly increases efficacy, especially against symptomatic infections, even when caused by disturbing SARS-CoV-2 variants.
An even longer interval between the two doses. At 6 months instead of 2 months, it has been shown to lead to a greater increase in the immune response in adults.
Therefore, countries could consider a period of up to 6 months based on their epidemiological situation and the needs of the individual populations within them.