What happens if I get covid-19 just after receiving the first dose of the vaccine?

You have asked us what are the alternatives for a person who receives a first dose of the vaccine and, for whatever reason, tests positive for covid-19 a few days after the jab: will they receive the second injection if they have already been given an appointment, or will they have to wait? Does it make no difference? We looked into it.

As the global vaccination campaign progresses, there is also an increase in the number of cases where those vaccinated test positive for covid-19. This is to be expected: all injections are designed to prevent the vast majority of cases from dying from covid-19 or developing severe disease, but not from becoming infected. 

It is important to remember that when you are infected after vaccination, you are not being reinfected (a very rare event), but rather you are having what are known as breakthrough infections or “vaccine failures". In these cases, what happens is that the immunity generated is not as high as if we had two doses, and therefore, the risk of contracting the virus is higher. 

Moreover, according to Adelailda Sarulkhan, immunologist and scientific writer at the Institute for Global Health (ISGlobal in Catalan) in Barcelona, "the most recent data (table 4) show that a single dose of the vaccine – from both Pfizer and AstraZeneca – protects much less against [the delta variant] than against [the alpha variant]" and that "two doses are necessary to achieve comparable protection". This is a fact to be taken into account in the current context, in which the delta variant is becoming more and more spread in Spain, and where we are experiencing an increase in incidence in all the population groups (including those where the majority have already received the full regimen).

What happens in these cases?

The Ministry of Health's answer is quite clear: "If it is a person over 65 years, they will wait until they recover and finish the isolation period and the second dose will be administered, provided that at least the established period has passed between doses". On the other hand, if the person is 65 years of age or younger, "they will wait 6 months to complete the vaccination schedule with the administration of the second dose".

The reason for this measure "is twofold", Adelaida Sarukhan, immunologist and scientific writer at the Institute for Global Health (ISGlobal) in Barcelona, told Verificat. "On the one hand, older people tend to develop a less strong (and probably less durable) immune response, either through vaccination or natural infection, and, on the other hand, they are more vulnerable to dying from the disease if they become infected.

In contrast, she continues, "people under 65 have a more robust immune response. In this population group, natural immunity has been found to last at least six to nine months (probably years), so it is considered that, between immunity from the first dose and natural immunity from infection, they are protected for at least 6 months," she concludes.