Four Factors That Increase the Risk of Vaccinated People Getting COVID

Two weeks after your second dose of COVID-19 vaccine, the protective effects of vaccination will be highest. You are currently fully vaccinated. If you still get COVID-19 after this point, you have contracted a “breakthrough” infection. In general, breakthrough infections are similar to regular COVID-19 infections in unvaccinated people, but there are some differences. Here’s what to look for if you’ve had both shots.

According to the COVID Symptom Study, the five most common symptoms of a breakthrough infection are headache, runny nose, sneezing, sore throat and loss of smell. Some of these are the same symptoms that people have who have not had any vaccine experience. If you are not vaccinated, three of the most common symptoms are also headache, sore throat and runny nose.

However, the other two most common symptoms in the unvaccinated are fever and a persistent cough. These two “classic” COVID-19 symptoms are much less common once you’ve had your shots. One study found that people with breakthrough infections are 58% less likely to develop a fever than unvaccinated people. On the contrary, COVID-19 after vaccination has been described to many as a cold.

Vaccinated people are also less likely to be hospitalized than unvaccinated people if they develop COVID-19. They are also likely to have fewer symptoms during the early stages of the disease and are less likely to develop COVID for a long time.

The reasons why the disease is milder in vaccinated people may be because vaccines, if they don’t block the infection, seem to cause infected people to have fewer virus particles in their bodies. However, this has yet to be confirmed.

What increases the risk?

In the UK, research has shown that 0.2% of the population – or one person in every 500 – experiences a breakthrough infection once fully vaccinated. But not everyone runs the same risk. Four things appear to contribute to how well you are protected by vaccination.

1. Vaccine Type

The first is the specific vaccine type you received and the relative risk reduction each type offers. Relative risk reduction is a measure of how much a vaccine reduces the risk of someone developing COVID-19 compared to someone who has not been vaccinated.

Clinical studies have shown that the Moderna vaccine reduced a person’s risk of developing symptomatic COVID-19 by 94%, while the Pfizer vaccine reduced this risk by 95%. The Johnson & Johnson and AstraZeneca vaccines underperformed, reducing this risk by approximately 66% and 70% respectively (although the protection provided by the AstraZeneca vaccine appeared to increase to 81% if there was a longer interval between doses). was left).

2. Time Since Vaccination

But these numbers don’t give the full picture. It is becoming increasingly clear that the length of time since vaccination is also important and is one of the reasons why the debate over booster vaccinations is growing in intensity.

Those in the first wave of UK vaccination programs may have had their first dose more than eight months ago.

Early research, still in pre-print (and thus yet to be assessed by other scientists), suggests that the protection of the Pfizer vaccine decreases in the six months after vaccination. Another preprint from Israel also suggests that this is the case. It’s too early to know what will happen to vaccine efficacy after six months in the double vaccinated, but it will likely decline further.

3. Variants

Another important factor is the variant of the virus you are dealing with. The above risk reductions were largely calculated by testing vaccines against the original form of the coronavirus.

But when faced with the alpha variant, data from Public Health England suggests that two doses of the Pfizer vaccine is slightly less protective, reducing the risk of developing COVID-19 symptoms by 93%. Against delta, the protection level drops even further, to 88%. The AstraZeneca vaccine is also affected in this way.

The COVID symptom study supports all of this. The data suggests that in the two to four weeks after receiving your second Pfizer shot, you are about 87% less likely to develop COVID-19 symptoms when faced with delta. After four to five months, that figure drops to 77%.

4. Your immune system

It is important to remember that the above numbers refer to the average risk reduction in a population. Your deductible will depend on your own level of immunity and other person-specific factors (such as how exposed you are to the virus, which may be determined by your job).

Immune condition generally declines with age. Long-term medical conditions can also affect our response to vaccination. The elderly or those with compromised immune systems may therefore have a lower level of vaccine-induced protection against COVID-19, or may see their protection diminish more quickly.

People with certain conditions or certain medications may offer less protection against COVID-19 after vaccination.

It’s also worth remembering that the most clinically vulnerable were given their vaccines first, possibly more than eight months ago, which may increase their risk of a breakthrough infection due to diminishing protection.

Should you be concerned?

Vaccines still greatly reduce your chances of getting COVID-19. They also protect against hospitalization and death to an even greater degree.

It’s about seeing breakthrough infections, though, and the concern is that they could increase if vaccine protection, as suspected, declines over time. That’s why the UK government plans to give booster doses to the most vulnerable, and is also considering whether boosters should be given more widely. Other countries, including France and Germany, are already planning to offer boosters to groups believed to be at higher risk for COVID-19.

But even boosters are eventually used, this should not be interpreted as vaccines that don’t work. And in the meantime, it is essential to promote vaccination to all those who qualify and who have not yet been vaccinated.

Written by:

Vassilios Vassiliou – Senior Clinical Lecturer in Cardiovascular Medicine, University of East Anglia Ciaran Grafton-Clarke – NIHR Academic Clinical Fellow, Norwich Medical School, University of East Anglia Ranu Baral – Visiting Researcher (Academic Foundation Doctor FY2), University of East Anglia

This article was first published in The Conversation.