Two weeks after your second dose of the Covid-19 vaccine, the protective effects of the vaccine will be at their highest level. At this point, you are fully vaccinated. If you are still contracting Covid-19 after this milestone, you have suffered from a “breakthrough” infection. Generally speaking, progressive infections are similar to common Covid-19 infections in unvaccinated people, but there are some differences. This is what to watch out for if you have had both doses.
According to him 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 experienced by people who have not been vaccinated. If you haven’t, 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 persistent cough. These two symptoms “Classics” of Covid-19 become much less common once you have received the injections. A study has found that people with breakthrough infections are 58% less likely to have a fever compared to unvaccinated people. Rather, it has described that Covid-19 after vaccination feels like a cold to many.
Vaccinated people are also less likely than unvaccinated people of being hospitalized 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 a Extended Covid.
The reasons why the disease is milder in vaccinated people could be because vaccines, if they do not block the infection, seem to lead to infected people having fewer virus particles on your body. However, this has yet to be confirmed.
In the UK, a investigation has found that 0.2% of the population, or one person in 500, experiences progressive infection once they are fully vaccinated. But not everyone is at the same risk. Four things seem to contribute to how well you are protected by vaccination.
The first is the specific type of vaccine 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 was not vaccinated.
Clinical trials found that the Moderna vaccine reduced a person’s risk of developing symptomatic Covid-19 in a 94%, while the Pfizer vaccine reduced this risk by 95%. The Johnson & Johnson and AstraZeneca vaccines performed worse, reducing this risk by approximately one 66% and 70% respectively (although the protection offered by the AstraZeneca vaccine seemed increase to 81% if a longer interval between doses was left).
But these figures don’t paint the whole picture. It is increasingly clear that the time elapsed since vaccination is also important and it’s one of the reasons why debate on booster vaccines it is increasing in intensity.
The first investigations, still in prepress (and therefore have yet to be reviewed by other scientists), suggest that the protection of the Pfizer vaccine decreases during the six months after vaccination. Other pre-established from Israel also suggests that this is the case. It is too early to know what happens to the efficacy of the vaccine beyond six months in the double vaccinated, but it is likely to be further reduced.
Another important factor is the variant of the virus you are dealing with. The risk reductions mentioned above were largely calculated by testing vaccines against the original form of the coronavirus.
But when faced with the alpha variant, the data from Public Health England suggest that two doses of the Pfizer vaccine are slightly less protective, reducing the risk of contracting 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. Their data suggest that in the two to four weeks after receiving your second dose of Pfizer, you are about 87% less likely to have Covid-19 symptoms when faced with Delta. After four to five months, that number drops to 77%.
It is important to remember that the above figures refer to the average risk reduction in a population. Your own risk will depend on your own immunity levels and other factors specific to the person. (such as how exposed you are to the virus, which could be determined by your job).
Immune fitness generally declines with age. Long-term medical conditions can also affect our response to vaccination . Therefore, older people or people with compromised immune systems may have lower levels of protection induced by the Covid-19 vaccine, or they may see their protection diminish more quickly.
It is also worth remembering that the most clinically vulnerable received their vaccinations first, possibly more than eight months ago, which may increase their risk of experiencing a breakthrough infection due to decreased protection.
However, it is worrisome to see breakthrough infections, and the concern is that they could increase if the protection of the vaccine, as suspected, falls over time. Therefore, the UK government plan giving a booster dose 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 reinforcements to groups that are considered to be at increased risk from Covid-19.
But even the reinforcements end up being used, this should not be construed as that vaccines do not work. And in the meantime, it is essential to promote vaccination among all those eligible who have not yet been vaccinated.
*Vassilios Vassiliou Senior Clinical Professor of Cardiovascular Medicine, University of East Anglia
**Ciaran Grafton-Clarke NIHR Clinical Academic Fellow, Norwich School of Medicine, University of East Anglia
***Ranu Baral Visiting Fellow (Academic Foundation Doctor FY2), University of East Anglia