Can I still get covid even though I have been vaccinated?

BarcelonaCovid vaccines are effective. The over 3,290 million doses administered in the world prove it, but also the paradigm shift that has been taking place in Catalonia for a few weeks. Despite the uncontrolled explosion of new infections especially among the youngest people, hospitalizations and deaths have been decoupled from the curve of contagion. Unlike other waves, the rampant transmission of the fifth wave is not resulting in a massive increase in admissions or deaths, although there is a spike in emergency room visits among those younger than 30 and some patients are also arriving in intensive care units (ICUs), especially people between 40 and 69 years of age.

The differentiating factor is vaccines. Complications due to covid are mainly associated with age: the older the person is, the higher the risk of suffering them. In Catalonia, the population over 70 years of age has been highly vaccinated (two doses) for months and cases among this population are generally anecdotal and mild. On the other hand, other vulnerable age groups continue with the immunization halfway (from 30 to 69 years) and the rest have practically not started it (younger than 29 years) and, therefore, are more exposed to the virus and its consequences.

Seven months after the vaccination campaign began, the protective effects of the vaccine can already be seen. But do the vaccines work the same for everyone, is it possible to get infected once you have been vaccinated, do the vaccines prevent infections or do they only protect against serious illness?

1. Vaccines don't immunize everyone

Covid vaccines have been shown to be more than 90% effective, but none are foolproof. It is estimated that approximately 10% of people who are vaccinated do not develop the desired immunity, regardless of the vaccine they are given.

This problem is associated with age, especially among people over 65, who usually have a weaker immune system, and with serious illnesses, such as people with cancer or who are immunosuppressed (i.e., were born with a non-existent or defective immune system or have received therapies that have destroyed their defenses). Some of these people are at risk of becoming ill if they are exposed to the virus and become infected, even if they have been vaccinated, and for that reason it is not ruled out that there may be serious cases or that some of these vaccinated people die.

These coverage problems are not specific to the covid vaccine. The flu vaccine, for example, works only among half of those vaccinated, but despite being able to catch it, they do not usually have serious cases because the vaccine always confers some degree of protection. The same happens with other vaccines that are very integrated in immunization programs, such as polio, which has 99% efficacy and despite being very good there is room for non-immunization; mumps (88%); whooping cough (85%), or hepatitis B (90%).

2. Vaccinated people can also be infected

There are cases of coronavirus among vaccinated people, but the vast majority are protected against the disease or at least against its most severe forms. In Catalonia, 0.2% of those immunized have been infected after receiving the first dose and 0.12% after the second, and according to the Department of Health they are usually mild cases.

Given the speed of spread of the current virus (each positive is generating at least three new infections) and the predominance of the delta variant, which would be more than 50% more contagious than the British, it is likely that this figure may increase in the coming days.

3. Immunity is not automatic

Vaccines do not have a direct and immediate effect on the immune system, but stimulate it indirectly. In double-dose schedules, the first dose is often referred to as a memory because it has a limited effect and antibodies decline over time, while the second dose is called the booster because it brings these defences back up and stabilises them at higher levels over a period of time.

The highest protection with Pfizer is obtained 7 days after the second dose, with Moderna it takes 14 days after the second dose and with AstraZeneca 28. With Johnson & Johnson, the only single-dose covid vaccine, maximum protection is achieved 14 days after administration.

4. Second dose prevents severe cases

Currently, a first dose of the vaccine protects between 32% and 38% when it comes to suffering symptoms in the case of infection, 10% less than when the hegemonic variant was the British one, according to studies carried out by the Department of Health of the UK. With the two doses, however, the protection shoots up to 80%.

On the other hand, the effectiveness against serious diseases and hospitalization is not compromised by the delta: with one dose the vaccine already provides 80% protection, and with two doses the figure rises to 96%. For this reason, health authorities stress the importance of having the two doses at the right time intervals.

5. Vaccinated people can transmit the virus

Preventing infection and preventing disease are different things. Vaccines were created and tested to prevent disease, and their inoculation is associated with a decrease in viral load and transmission capacity, but this does not mean that it can stop new infections.

Immunized people can be infected and not know it (asymptomatic) or suffer some mild symptoms, but in both cases they can act as spreaders and infect their environment. The Department of Health says that with the British variant it was observed that vaccination cut the spread in 50% of cases in the homes of vaccinated people and, therefore, that there were fewer infections, but now, with the delta, there is still no data.

6. Risk for those who have passed the infection

It is already known that the vast majority of people who have passed the disease develop a protective immunity, although its duration is not yet known. At the very least, it has been shown to last six months, but there are also studies that suggest that it could last eight months or even twelve.

In these cases, a single dose is sufficient to induce an immune response equal to or greater than that observed after two doses in people who have not had the disease. The infection acts as a stimulus to the immune system and serves as a first dose, so that a further injection will act as a booster. As long as this vaccine does not arrive, the person may become infected again.

7. Preventive measures are needed

Until a large part of the population is vaccinated against the coronavirus -at least 70%-, health authorities insist that it is essential to continue to comply with preventive measures to prevent the spread of the disease, especially for those people who despite being vaccinated do not develop immunity.

Thus, it is important to get vaccinated but also continue using the mask, especially when bubble groups are mixed; wash hands frequently; ensure interpersonal distance; prioritize outdoor or well ventilated spaces, and stay home if you have symptoms compatible with covid (dry cough, fever for three days, muscle pain, headache, diarrhoea, nausea or vomiting, loss or decrease of sense of smell and taste), if you are waiting for the result of a diagnostic test or have been in contact with a positive case.